Immunology Flash Cards

8/10/2019 Immunology Flash Cards

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IMMUNOLOGY FLASH CARDS

1. Variolation2. Who introduced vaccination?3. Who is the father of microbiology?4. Who introduced antiseptic techniques for surgery?5. When were antibiotics developed?6. When were antibiotics commercialized?

1. Injection of crusted material from smallpox blisters used to immunize in ~16th century2. Jenner for smallpox in England, late 1700s Inoculated cowpox (vaca Latin for cow)3. Pasteur (1860s) Showed bacteria could be killed by heat Developed chicken cholera, anthrax, and rabies vaccines4. Lister 5. 1920s6. 1940s

1. Antigen

2. Immunogen

3. Hapten

4. Tolerogen

5. Epitope

1. Chemical foreign to host which induces immune response Reacts w/antibodies2. Induces an immune response (does not necessarily react w/antibodies) ex. bovine serumalbumin (BSA)3. Antigen that alone does NOT induce immune response Eg penicillin, dinitrophenyl (DNP) Not immunogenic b/c they cannot activate helper T cells (cant bind to MHC proteins) They can stimulate a response when covalently bound to a carrier protein (such as BSA)4. Antigen altered to induce tolerance (no immune response)5. An antigenic determinant (confers specificity for Ab)


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1. Defensins

2. Acute phase proteins

1. Proteins secreted by phagocytes Have antimicrobial effects

2. Produced mainly by liver Similar to defensins Bind to microbes, making them more susceptible to being destroyed Ex. C-reactive protein, mannose-binding protein

Innate (nonspecific) immunity

Protects against microbes in general Classified into 3 major categories:o Physical barriers (skin, mucous membranes) Fatty acids secreted by sweat glands have antibacterial and antifungal activityo Phagocytic cells (neutrophils, macrophages, NKs)o Proteins (complement, lysozyme, interferon) Requires complement, cytokines and leukocyte

Give examples of how reduced phagocytosis predisposes people to infection

1. _ Infections in children w/defects in phagocytic process Chronic granulomatous disease: NADPH oxidase defect cant generate H2O2 cant kill

bacteria Chediak-Higashi syndrome: abnormal lysosomal granules cannot fuse w/phagosome2. Frequent infections occur in pts w/PMN counts


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Acquired (adaptive/specific) immunity

Protects against a particular microbe Requires lymphocytes and antibodies Gets more intense w/each antigen exposure, therefore displaying immune memory

Results either from:o Exposure to the organism (active immunity) OR o Receipt of preformed antibody made in another host (passive immunity) MEMORY response is the adaptive immunity responseo This is controlled by lymphocyteso Lymphocytes are very specific in their antigen recognition and response

Passive acquired immunity

Temporary protection against an organism

Acquired by receiving serum containing Abs from another person or animal (i.e. you dontmake the Abs) Transplacentalo Thru placenta (IgG)o Thru breast milk (IgA) Serum therapyo Ex. infusion of serum w/Abs upon hepatitis exposure Advantage: protective abilities are present immediately, whereas active immunity has delay Disadvantage: [Ab] _ fast protection lasts 1-2 months

Active acquired immunity Protection based on exposure to organism Slower onset but longer duration than passive immunity Advantage: anamnestic (2ndary) response occurs Abs protect against organisms by:o Toxin neutralization, lysis of bacteria in presence of complement, opsonization (helps

phagocytosis) T cells mediate variety of rxns including:o Destruction of virus-infected cells and bacteria, macrophage activation, delayedhypersensitivity Convalescence exposed to Ag, then more immune Vaccine administration of antigens


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Diseases and abnormalities that predispose to infections

1. Diabetes Often have S aureus infections, perhaps b/c:o Extensive atherosclerosis (causes tissue anoxia)

o Defect in neutrophil function2. Sickle cell anemia Often have Salmonella osteomyelitis3. Pts w/certain congenital cardiac defects Predisposed to endocarditis caused by streptococci Neutrophils have difficulty penetrating vegetations formed on valves in endocarditis4. Pts w/an anortic aneurysm Prone to vascular infections by Salmonella species

Two components of the acquired (adaptive) immune system

1. Cell-mediated immunity Consists primarily of killer T cells Utilizes lymphocytes, cytokines, phagocytes Inhibits organisms (fungi, parasites, and certain intracellular bacteria) Kills virus-infected cells and tumor cells2. Antibody-mediated (humoral) immunity Consists primarily of B cells (and plasma cells) Utilizes antibodies and complement Neutralizes toxins and viruses

Opsonizes bacteria (makes them easier to phagocytize)

What bridges the two arms (cell-mediated and humoral immunity) of acquired immunity?

Macrophages and certain other phagocytic cells such as dendritic cellso Participate in both the innate and acquired armso As part of innate arm ingest and kill microbeso As part of acquired arm present antigen to helper T cells (essential 1st step in activation of

acquired arm) Note: neutrophils (which are phagocytes have excellent microbicidal abilities) DO NOT present antigen to helper T cells and therefore function in innate BUT NOT acquired immunity


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RAG

Recombinase activating gene Helps in the formation of lymphocyte receptors Part of a family of genes that evolved allowing adaptive immunity

After these genes evolved, lymphocytes became major player in immunity

Antigen recognition

1. Cognitive (recognition) phase Lymphocyte recognizes a foreign antigen by means of a receptor 2. Activation phase Proliferation and differentiation of lymphocytes expression of new genes, acquire newfunctions

3. Effector (response) phase Effector lymphocytes newly functioning, eliminate antigen Some lymphocytes differentiate into memory cells

Steps in cell-mediated immunity: Bacterial infection

1. Macrophage ingests microbe (eg M tuberculosis)2. Fragments of microbe antigens or epitopes appear on surface of macrophage in associationw/MHC II proteins

3. Antigen-class II MHC protein complex interacts w/antigen-specific receptor on helper T cell4. Helper T cell is activated and proliferates as result of IL-1 (produced by macrophages) and IL-2 (produced by lymphocytes)5. Activated helper T cells, w/activated macrophages, mediate delayed hypersensitivity rxnspecifically against M tuberculosis

Steps in cell-mediated immunity: Viral infection

1. Virus is inhaled and infects cell of respiratory tract

2. Viral glycoproteins appear on surface of infected cell in association w/class I MHC proteins3. Cytotoxic T cell binds to viral antigen-class I MHC complex stimulates T cell to grow into aclone of cells by IL-2 (produced by helper T cells)4. These cytotoxic T cells specifically kill influenze virus-infected cells by: Recognizing viral antigen-class I MHC protein complexes on cell surface Releasing perforins that destroy membrane of infected cell


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Steps in antibody-mediated immunity

1. Involves cooperation of macrophages, TH cells, & B cells2. After processing by macrophage, fragments of antigen appear on its surface in association

w/class II MHC proteins3. Antigen-class II MHC protein complex binds to specific receptors on helper T cell (TCR = Tcell receptor) T cell produces IL-2, IL-4, and IL-54. These factors activate B cell B cell proliferates & differentiates plasma cell Igs5. Specificity of response is provided by: Antigen receptor (TCR) on T cells Antigen receptor (IgM) on B cells Note: interleukins are not specific

What two important functions do B cells perform during induction process?

1. They recognize antigens w/their surface IgM that acts as an antigen receptor 2. They present epitopes to TH cells in association w/class II MHC proteins3. Note: IgM antigen receptor on B cell can recognize foreign proteins, carbs, lipids, DNA, RNA, etc. Class II MHC proteins of B cell can only present peptide fragments to TH cells

Soluble mediators of immunity

1. Acute phase proteins Induced by stress (infection, injury) Participate in inflammation and healing Ex. C-reactive protein, serum amyloid2. Complement Activated by immune complexes Participate in immune regulation3. Cytokines Produced by all cells in body4. Antibodies Bind antigen to form immune complex Five classes: IgM, IgA, IgG, IgE, and IgD


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Clonal Selection

1. Antigen selects a B cell endowed w/the preexisting capacity to make the specific antibody

for that antigen2. Each person has a large pool of B cells3. Each B cell bears specific receptor (either IgM or IgD) that can react with 1 antigen (or closelyrelated group of Ags)4. An antigen interacts w/B cell w/best fit Ig surface receptor Stimulates B cells to proliferate and form clone of cells Selected B cells plasma cells Ig specific for Ag5. Clonal selection also occurs with T cells Antigen interacts w/specific receptor on a Th or Tc cell This selects cell expands into clone of cells with the same specificity

Consequences of immune activation

1. Inflammation Innate immunity, influx of factors and cells, PMNs2. Phagocytosis Ingestion of particles by macrophages and neutrophils3. Neutralization Ab combines w/antigen and inactivates it4. Cytotoxic reaction

Killer cells interact w/target cell and kill it

Origin of immune cells

1. In post-natal life, stem cells reside in bone marrow2. T cells mature into immunocompetent cells in thymus Stem cells lack antigen receptors CD3, CD4, and CD8 First differentiate to express both CD4 and CD8 If contacts cell w/class II MHC proteins CD4+ cell If contacts cell w/class I MHC proteins CD8+ cell


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Thymic education

Two processes that occur in thymus 1. CD4+ and CD8+ cells bearing antigen receptors for self proteins are killed (clonal deletion)

by apoptosis Removal of these self-reactive cells = negative selection Results in self tolerance (prevents autoimmune rxns)2. CD4+ and CD8+ cells bearing antigen receptors that do not react w/self MHC proteins arekilled Results in positive selection for T cells that react well w/self MHC proteins These 2 processes produce T cells selected for their ability to react both w/foreign antigens andwith self MHC proteins

MHC proteins

Major histocompatibility complex Perform 2 essential functions in immune response:o Positive selection of T cells in thymuso Presentation of antigens to T cells, the initial step required to activate those cells Most imp antigens recognized in graft rejection process

GALT

gut-associated lymphoid tissue Up to 40% of T cells develop here rather than thymus These intraepithelial lymphocytes are thought to provide protection against intestinal pathogenso Their antigen receptors and surface proteins are different from those of thymus-derived T cellso Cannot substitute for thymus-derived lymphocytes Evidence: pts w/DiGeorges syndrome (lack a thymus) are profoundly immunodeficient

Sepsis

The presence of pathogenic organisms, or their toxins, in the blood or tissues I.e. blood infection that causes disease/symptoms

Ex. may have bacteremia but no symptoms, thus NOT septic


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Hematopoiesis

1. Blood cells are short lived and are thus continuously renewed from pluripotent stem cells in bone marrow

Pluripotent under influence of cytokines, stem cells become a variety of other cells Exception: memory cells, progeny of which last for yrs2. Process is controlled by cytokines IL-7 imp for B cell development IL-3 acts on early bone marrow progenitor cells3. GM-CSF - stimulates cells of granulocytic & macrophage4. M-CSF (macrophage colony stimulating factor)5. G-CSF (granulocyte colony stimulating factor) Used clinically _ speeds up bone marrow recovery

T lymphocytes: Subtypes and Markers

Subtypes:o TCR a/b or g/do Th-1 T helper cello Th-2 T helper cello Tc T cytotoxic cello Ts T suppressor cello NK natural killer (large granular lymphocyte) Surface markers (CD = cluster designation)o All T cells TCR, CD3 (TCR complex)

o Th cells CD4o Tc cells CD8o NK cells receptors for class I MHC, CD16

TCR complex

Formed by 2 portions (TCR + CD3), totaling 7 proteinso TCR complex: ab-gden TCR portion, a/b or g/d, binds the antigen Rest of the proteins is the CD3 portiono CD3 transfers signal across membrane into T cell T cells with g/d TCR primarily located in mucosao CD8+ (cytotoxic T cells) onlyo Limited antigenic repertoire (100 1000 clones) T cells with a/b TCR are found in the bloodo ~108 different cloneso CD4+, CD8+, or suppressor T cellso MHC restricted


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1. Th cells2. Tc cells3. Ts cells4. NK cells

1. Two types distinguished by cytokines they secrete: Th1: produces IL-2 and IFNo Involved in cell-mediated immunity Th2: produces IL-4 and IL-10o Involved in humoral immunity3. TCR, CD8 Bind to targets and release killer molecules4. CD4 and CD8 Release suppressor cytokines5. CD16 (NO TCR) Ag receptor less defined

Which cells express MHC class I? MHC class II?Which cells do MHC classes present to?

All nucleated cells express MHC class I Only APCs express MHC class II (as well as class I)o Langherans cells (in skin)o Interdigitating cells

o Macrophageo Follicular dendritic cellso B cells Antigens must be presented to T cells by an APC MHC I cells present antigen to CD8+ cells MHC II cells present antigen to CD4+ cells

Helper T cell produces cytokines. Name them and their function.

1. IL-4 and IL-5

Help B cells produce Abs2. IL-2 Activates CD4 and CD8 cells3. IFNg Actives macrophages (the main mediators of delayed hypersensitivity against intracellular organisms such as M. tuberculosis)


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What enzymes are involved in the signal transduced by CD3, CD4, and CD8?

1. CD3 One of its transmembrane proteins the zeta chain is linked to a tyrosine kinase called fyn2. CD4 and CD8

May signal via tyrosine kinase lck

Function of CD4 lymphocytes

1. Th-2 cells Help B cells develop into Ab-producing plasma cells by producing IL-4 and IL-5 (influencehumoral immunity)2. Th-1 cells Help CD8 T cells to become activated cytotoxic T cells by producing IL-2, activate NK cells Help macrophages effect delayed hypersensitivity (eg, limit infection by M tuberculosis) by

producing primarily IL-2 and gamma IFN (i.e. activate macrophages) Also activate NK cells Thus influence CMI

What is the main thing that regulates the balance between Th-1 and Th-2 cells?

IL-2 levelso Produced by macrophageso Increases the number of Th-1 cellso Thus enhances: Host defenses against organisms controlled by delayed hypersens response

Cell-mediated immunity Gamma IFNo Inhibits production of Th-2 cells

1. Cleaved viral peptides associate w/which MHC class?

2. Which MHC class do all other antigens associate with?

1. Class Ia. Viral peptides associate w/class I MHC protein

b. Complex is transported to surface, where viral antigen is presented to receptor on CD8+ cell2. Class IIa. Foreign protein is cleaved into peptides that associate w/class II MHC proteins

b. Complex is transported to surface of APC, where antigen, in association w/class II MHC protein, is presented to receptor on CD4+ helper cellRemember the rule of eight:CD4 cells interact w/class II, CD8 cells interact w/class I


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Activation of T cells

1. Requires that they recognize a complex on surface of APCs consisting of both the antigen anda class II MHC protein2. 1st step antigen interacts w/TCR specific for that antigen

CD4 on Th cell also interacts w/class II MHC protein Other proteins also help stabilize contact between T cell & APC (LFA-1 on T cell binds toICAM-1 on APCs)3. For full activation of Th cells, costimulator is required B7 protein on APC must interactw/CD28 protein on Th cell If costimulatory signal occurs: IL-2 is made by Th cell Th cell capable of performing all of itsfunctions If costimulatory signal does not occur: state of unresponsiveness called anergy ensues

Accessory events in T cell activation

1. Receptors imp in adhesive events LFA-1 (leukocyte functional antigens) Located on CD4 expressing helper T cells Interacts with ICAM-1 (intercellular adhesion molecule) on APC LFA-3 Located on class I MHC expressing target cell Interacts with CD2 on the CD8 expressing Tc cell2. Zeta chain, along with CD3 molecule, also important

Enhances activation process Noncovalently interacts w/TCR and MHC complex with CD4 on helper T cells or CD8 oncytotoxic T cells

CTLA-4

Protein that appears on the T cell surface after the T cell has been activated Binds to B7 by displacing CD28

Interaction of B7 with CTLA-4 inhibits T cell activation by blocking IL-2 synthesiso This restores activated T cell to a quiescent state and thus plays an imp role in T cellhomeostasis Mutant T cells that lack CTLA-4 participate w/increased frequency in autoimmune rxns Administration of CTLA-4 reduces the rejection of organ transplants in experimental animals


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What to T cells recognize?

1. Polypeptide antigens ONLY2. Furthermore, they recognize those polypeptides ONLY when they are presented in associationw/MHC proteins

3. Th cells recognize antigen associated w/class II MHC protein4. Tc cells recognize antigen associated w/class I MHC proteins This is called MHC restriction: the 2 types of T cells are restricted b/c they are able torecognize antigen ONLY when antigen is presented w/the proper class of MHC protein

Class I MHC proteins

Generally present endogenously synthesized antigens (eg. Viral proteins)o Proteins are cleaved by a proteosome

o Peptide fragments associate w/a TAP transporter that transports the fragment into the rER where it associates w/the class I MHCo Complex of peptide fragment and class I MHC protein then migrates via Golgi to cell surface Killed viral vaccines do not activate Tc cells b/c virus does not replicate w/in cells and thereforeviral epitopes are not presented in association with class I MHC proteins

Class II MHC proteins

1. Present the antigens of extracellular microorganisms that have been phagocytized (eg.Bacterial proteins)

Extracellularly acquired proteins are cleaved to peptide fragments within an endosome, wherethe fragment associates w/class II MHC proteins This complex then migrates to the cell surface2. An invariant chain is attached to the class II MHC proteins when they are outside of theendosome Chain degraded by proteases w/in endosome, allowing peptide to attach to class II MHC w/incompartment Prevents endogenously synthesized proteins from associating w/class II MHC proteins

How do B cells interact with antigens?

Unlike T cells, they interact directly with antigens via their surface antigen receptors (IgM andIgD)o Antigens do NOT have to be presented to B cells in association w/class II MHC proteins IgM and IgD recognize many different types of molecules, such as peptides, polysaccharides,nucleic acids, small chemicals (penicillin)


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Describe the events that occur when the antigen-MHC complex on the APC interacts with theTCR.

1. Signal is transmitted by CD3 complex thru several pathways that lead to a large influx of Ca+into the cell

2. Ca+ activates calcineurin, a serine phosphatase3. Calcineurin activates genes for IL-2 and the IL-2 receptor 4. IL-2 (T cell growth factor) stimulates: Th to multiply into a clone of antigen-specific Th cells Most cells of this clone perform effector and regulatory functions, some become memorycells Tc cells to produce gamma interferon IFN gamma _ expression of class II MHC proteins on APCs enhances ability of APCs to

present antigen to T cells & upregulates immune response

Memory T cells

Endow host defenses w/ability to respond rapidly and vigorously for many years after initialexposure antigen This memory response to a specific antigen is due to:o Many memory cells are produced, so that sec-ondary exposure is greater than primary responseo Memory cells live for many years or have the capacity to reproduce themselveso Memory cells are activated by smaller amounts of antigen and require less costimulationo Activated memory cells produce greater amounts of interluekins than do nave T cells whenthey are first activated

T cell receptor (TCR)

1. Similar to Ig heavy chains in that: Genes coding for them are rearrangements of DNAs There are V (variable), D (diversity), J (joining), and C (constant) segments that rearrange to

provide diversity Genes (RAG-1 and RAG-2) that encode enzymes that catalyze these rearrangements are similar in T & B cells2. Each T cell has a unique TCR on its surface Millions of different T cells exist in each person, and activated T cells (like activated B cells)clonally expand3. TCR is different in 2 ways: It has 2 chains rather than 4 Recognizes Ag only in conjunction w/MHC proteins


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Effector functions of T cells

1. Delayed hypersensitivity Produced against antigens of intracellular microorganism Mediated by macrophages and CD4 cells (esp Th-1)

2. Cytotoxicity Concerned w/destroying virus-infected & tumor cells To kill virus-infected cell, Tc cell must recognize both viral antigens and class I molecules onsurface of infected cell AND receive a cytokine stimulus from a Th cell Note: Infected cell can also be killed by antibody-dependent cellular cytotoxicity (ADCC)

How do Tc and NK cells kill virus-infected cells?

1. By inserting perforins into infected cell Form channel thru pm cell contents lost cell dies2. By inserting granzymes into infected cell

Trigger apoptosis by activating caspases (which destroy DNA repair)3. By activation of the Fas-Fas ligand (FasL) Fas is a protein on surface of many cells When a cytotoxic TCR recognizes an epitope on the surface of a target cell, FasL is induced inthe T cell When Fas & FasL interact, apoptosis of target cell occurs

Antibody-dependent cellular cytotoxicity (ADCC)

1. Combination of IgG and phagocytic cells that can destroy virus-infected cells2. Ab bound to the surface of the infected cell is recognized by IgG receptors on the surface of

phagocytic cells (eg, macrophages or NK cells)3. Infected cell is killed4. This process can also kill helminths (worms) In this case, IgE is the Ab involved and eosinophils are the effector cells

Regulatory functions of T cells

1. Antibody production Most Ab production requires Th cells (T cell-depen)2. Cell-mediated immunity Ag is processed by macrophages, is fragmented, and is presented w/class II MHC molecules on

the surface These interact w/receptor on Th cell stimulated to produce lymphokines (IL-2 = T cell growthfactor) stimulates specific Th and Tc cells to grow3. Suppression of certain immune responses Certain T cells can suppress Ab production Failure of such regulation may result in unrestrained Ab production to self antigens(autoimmune disease)


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T cell-dependent response

1. Ab production that requires the participation of Th cells2. Ex. B cells used as APC (macrophages commonly do this): Ag binds to IgM or IgD & is internalized w/in B cell

Ag fragments return to surface w/class II MHC mol. These interact w/TCR and, if B7 on B cell interacts w/CD28 on Th cell, Th cell produces IL-2,IL-4, & IL-5 IL-4 & -5 induce class switching (IgMIgG, IgA, IgE) B cell divides and differentiate into plasma cells Interleukins alone are not sufficient to activate B cells: CD40 ligand must interact w/CD40 on B cell Other proteins strength interaction between Th and B cell (LFA-1 on T cell w/ICAM-1 on Bcell)

T cell-independent response

1. Antibody production that is not dependent on Th cells2. Antigens that induce such a response are usually polymerized (multivalent) macromoleculessuch as bacterial capsular polysaccharide, DNA, RNA, many lipids Repeated subunits act as a multivalent antigen that cross-links the IgM antigen receptors on theB cell and activates it in absence of help from CD4 cells3. Primarily IgM is made (vs. T cell-ind response where all classes of Ab are made) This indicates that the lymphokines produced by the Th cell are needed for class switching4. Does NOT generate memory B cells

B cell functions

1. They differentiate into plasma cells and produce antibodies

2. They are APCs

B cell origin

1. B cell precursosrs first in fetal liver, then migrate to bone marrow where they remain duringadult life2. Maturation of B cells has 2 phases: Antigen-independent phase

Consists of stem cells, pre-B cells, and B cells Antigen-dependent phase Cells that arise subsequent to interaction with antigen (eg, activated B cells and plasma cells)3. B cells display surface IgM, the antigen receptor Surface IgM = monomer (circulating IgM = pentamer)4. Located in germinal centers of lymph n, white pulp of spleen, GALT


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B cell surface markers

1. Surface immunoglobulin (slg) Receptor for antigen (the B cell receptor) B cell-receptor complex = slg+Iga+Igb

Iga and Igb - heterodimer accessory molecules that appear on either side of slg; similar to CD3complex of T cell both function as signaling molecules when antigen binds to B cell-receptor complex2. Complement receptors (CR1 and CR2)3. Fc receptors Binds to Fc portion of Abs

Activation of B cell

Recognition phase:

1. Antigen binds to B cell IgM or IgD, endocytosis of antigenActivation phase:1. Antigen epitopes appear on surface w/class II MHC proteins2. Complex is recognized by Th cell w/a receptor for antigen3. T cell produces IL-2, IL-4, IL-5 growth & differentiation of B cell, isotype switching to IgG,affinity maturation4. Costimulatory interactions must occur for full activation: CD28 on T cell must interact w/B7 on B cell Required for activation of T cell to produce IL-2 CD40L on T cell must interact w/CD40 on B cell Required for class switching to IgG & other classes

End result of B cell activation

Effector phase:

1. Mature IgM and IgG expressing B cells produced IgM is most effective in activating complement2. Plasma cells produce Igs specific for the epitope Secrete thousands of Ab/sec for few days then die3. Some activated B cells form memory cells

Can remain quiescent for long periods but are capable of being activated rapidly upon re-exposure to antigen Most have surface IgG as Ag receptor, some have IgM Memory T cells secrete ILs that enhance memory B cell antibody production Thus rapid appearance of Ab in 2ndary response


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Macrophages (mononuclear phagocytes/monocytes)

1. Kidney shaped nucleus, large (10-20mm), granules w/lots of enzymes (ex. peroxidase, lipase, protease, elastase, etc.)2. Three main functions (1st CMI, 2nd humoral function):

Phagocytosis surface Fc receptors interact w/Fc portion of Igs, enhancing uptake of opsonizedorganism Antigen presentation present antigen fragments in association w/class II MHC for interactionw/the TCR Cytokine production IL-1 and TNF IL-1 activates Th cells TNF imp inflammatory mediator 3. Derived from bone marrow histiocytes4. Markers: MHC class II, Fc receptors, complement receptors

Granulocytes

All have polymorphonucleus, intermediate size, brightly stained granules1. Neutrophils (70% of blood)a. Predominant in blood, acute phase, phagocytic, release enzymes

b. Markers: Fc and complement receptors2. Eosinophils (5% of blood)3. Basophils (1% of blood

Natural killer cells (NK)

1. Imp role in innate host defenses

2. specialize in killing virus-infected cells and tumor cells3. Can kill w/o Ab, but Ab enhances their effectiveness (ADCC)4. Potently activated by IL-12 and gamma IFN5. Have receptors that detect presence of class I MHC If cell displays sufficient class I MHC cell is not killed (and vice versa)6. Kill by producing perforins and granyzmes, which cause apoptosis of target cell

Eosinophils

1. Its count is elevated in: Parasitic diseases (especially nematodes)

Hypersensitivity diseases (eg, asthma, serum sickness)2. Stimulated by IL-53. Function not clearly established4. Likely their main function is to defend against migratory larvae and discharge contents of their granules, which damages the cuticle of the larvae5. May also mitigate effects of immediate hypersensitivity rxns b/c granules of eosinophilscontain histaminase (enzyme that degrades histamine), which is an important mediator of immediate rxns


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Basophils and mast cells

1. Basophils WBCs w/blue granules

Circulate in blood stream2. Mast cells Fixed in tissue (esp under skin and in mucosa of respiratory and GI tracts)3. Both: Have receptors for Fc portion of heavy chain of IgE When adjacent IgE molecules are cross-linked by antigen, histamine and enzymes (eg,

peroxidases, hydrolases) are released inflammation and, in large amounts, cause severeimmediate hypersensitivity rxns

1. IL-1

2. IL-2

1. Produced mainly by macrophages, also epithelial cells, etc. Stimulator of inflammation (innate) & T cell (specific immunity) Its release is stimulated by LPS and T cells _ cAMP, _ nuclear factors, _ prostaglandins, _ adhesion molecules High concentrations _ - Endogenous pyrogen (Fever)- Cachexia Activates T & B cells, neutrophils, epithelial, fibroblasts

Ex. stimulates Th cells to differentiate and produce IL-22. Produced mainly by Th-1 cells Activates helper and cytotoxic T cells Activates B cells (acts synergistically w/IL-4) Induces LAK (lymphocyte activated killer) cells

1. IL-4

2. IL-5

1. Produced mainly by Th-2 cells Promote growth of B cells Enhances humoral immunity by _ Th-2 cells Required for class switching, enhances IgE synthesis2. Produced mainly by Th-2 cells Promote differentiation of B cells Enhances synthesis of IgA Stimulates production and activation of eosinophils


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1. IL-6

2. IL-3

1. Produced by Th cells

Stimulates B cells to differentiate Induces fever Induces production of acute-phase proteins in liver

2. Made by Th-2 cells Mediator of allergic airway disease (asthma) Shown to cause asthma in animals Involved in producing airway hyperresponsiveness

IL-10 and IL-12

1. Regulate the production of Th-1 cells IL-12: produced by macrophages, promotes Th-1 cells IL-10: produced by Th-2 cells, inhibits Th-1 cells (by limiting gamma IFN production)2. Relative amts of IL-4, IL-10 and IL-12 drive differentiation of Th-1 and Th-2 cells Therefore enhance either CMI or humoral immunity Imp medical consequences b/c main host defense against certain infections is either CMI or humoral

Ex. Leishmania infections in mice lethal if humoral response predominates but controlled if CMI predominates

1. IL-13

2. Transforming growth factor-b (TGF-b)

1. Mediator of allergic airway disease (asthma)

Made by Th-2 cells Binds to a receptor that shares a chain w/IL-4 receptor Involved in producing the airway hyperresponsiveness seen in asthma but does NOT _ IgE2. Inhibits growth and activation of T cells Anti-cytokine Also inhibits macrophages, B cells, neutrophils, NK cells Stimulates wound healing by _ synthesis of collagen Dampens/suppresses immune response when its no longer needed, promotes healing process


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Interferons

1. Block virus replication Alpha IFN

Produced by leukocytes Beta interferon Produced by fibroblasts2. Act as Lymphokines Gamma IFN Produced primarily by Th-1 and Tc cells, NK cells Potent activator of phagocytic activity of macrophages, NK cells, and neutrophils Can also _ synthesis of class I and II MHC proteins (thus enhancing antigen presentation)

Tumor necrosis factor (TNF-a)

1. Inflammatory mediator released primarily by macrophages2. At low concentrations beneficial effect _ synthesis of adhesion molecules by endothelial cells Activates respiratory burst w/in neutrophils _ lymphokine synthesis by Th cells Stimulates growth of B cells3. At high concentrations Mediator of endotoxin-induced septic shock Cachectin b/c it inhibits lipoprotein lipase in adipose, thereby _ utilization of fatty acids (resultsin cachexia)

Causes death and necrosis of certain tumors in animals Endogenous pyrogen

1. Lymphotoxin/TNF-b

2. Nitric oxide (NO)

3. Macrophage migration inhibitory factor (MIF)

1. Made by activated T cells, same effects as TNF-a2. Functions:

Mediator made by macrophages in response to endotoxin Vasodilation (mediator of hypotension in septic shock)3. Functions: Mediator made by macrophages in response to endotoxin Major role in induction of septic shock


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CD Leukocyte Markers

1. CD2 - costimulatory molecule that binds to LFA3 (integrin) On T and B cells, NKs, macrophages, neutrophils

2. CD3 TCR coreceptor 3. CD11a a costimulatory molecule that binds to ICAMs On T and B cells, NKs, macrophages, neutrophils4. CD16 another name for Fc receptor 5. CD19 B cell coreceptor 6. MHC II on APCs (T cells, B cells, macrophages) Bind to Ag, CD47. MHC I on T and B cells, NKs, macrophages, neutrophils Binds to Ag, CD8

1. Primary lymphoid organs

2. Secondary lymphoid organs

1. Foster the maturation of nave stem cells Thymus, bone marrow, bursa of Fabricus (in chicken)2. Contain mature cells and foster immune response Lymph nodes, spleen, and GALT Foreign Ag driven (unlike primary lymphoid organs)

Are both composed of lymphocytes, accessory cells (eg, APCs) and epithelial cells Epithelial cells can secrete factors that help in maturation and development of immune responseo Ex. thymic epithelial cells secrete thymosin, which promotes T cell maturation

Thymus

1. Fosters maturation of T cells2. Lymphoepithelial3. Divided into cortex and medulla4. Contain macrophages and dendritic cells that present self-antigens to differentiating T cells

leading to positive and negative selection5. Stem cells originally from bone marrow enter cortex positive and negative selection ensuesat corticomedullary junction6. Positively selected cells go on into medulla and out into body to secondary organs


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Bone marrow

1. Contains all the cells and cytokines necessary for B cell development2. preB immature B mature B

Spleen

1. Filters antigen out of blood and promotes immune response2. No spleen more susceptible to blood-borne infections3. Composed of capsule and reticular and cellular framework 4. Contains lymphocytes, APCs, and RBCs5. Divided into red pulp surrounding the white pulp White pulp surrounds central artery Contains PALS (peri-arteriole lymphatic sheath) which is where most of the T cells are located B cells clustered in germinal centers6. Blood flow enters via central branches of trabecular a. white pulp/PALS lymphatic nodule

marginal zone red pulp pulp veins trabecular veins splenic vein

Lymph nodes

1. Filters Ag from the lymph and supports immune response2. Composed of capsule, cortex and medulla Outer cortex follicle or B cell zones Inner cortex T cell zones Medulla Location of plasma cells3. Same structure as spleen: B cells surrounded by T cell4. Artery associates w/ high endothelial venule/HEV this is how components return to lymph

from the blood5. HEVs are specialized and found only in this area allow WBCs to get out of blood and intolymph node Imp if you have an infection in a node, lymphocytes of right clone can be called out of bloodinto node

Factors affecting immunogenicity

1. Protein complexes and particulate antigens are better than non-complexed proteins or solubleantigens (i.e. they engage APCs better better immune response)2. Route

Subcutaneous injection give best immune response Intradermal (I.D.) also good3. Dose Too little or too much can be inhibitory4. Adjuvants Substances that mix w/antigen thus engaging APCs Vaccines are given w/adjuvant (eg, Freunds adjuvants)5. Immune response potential (immune responses are variable)


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Rank order for antigen potency

1. Proteins > polysaccharides > nucleic acids > lipids2. Proteins are best immunogens Easily processed by APCs

Easily form non-covalent bonds w/MHC molecules and T and B cell receptors Complex proteins contain multiple epitopes per protein molecule arouses many clones (egmore than 1 T cell and/or B cell can bind to its various epitopes, thus eliciting different clones)

Lipopolysaccharides

1. Are endotoxins2. T-independent antigens (induce T-indep immune responses) Very limited immune response3. Contain 3 functional groups: Lipid A group stimulates B cells

Combines w/a serum protein This complex then binds to CD14 on B cells Core polysaccharide O antigen polysaccharide binds to B cell receptors (if that receptor is a clone w/affinity to Oantigen)

ABO Red Blood Cell antigens

1. Type O has Ab to both A and B, Type A has Ab to B, etc.2. Type and cross Type = tests RBCs w/antibodies to detect antigens

Cross-matching = tests serum for Abs3. Rhd glycoprotein on RBC surface Rhd+ = gene is expressed, Rhd- = gene is silent Ex. wife is Rh- and husband is Rh+ Fetus likely to be Rh+ mother begins to make Abs to Rh. If Ab is IgG it can cross placentaand result in hemolytic disease of newborns Will manifest only at a 2nd or later pregnancy Treatment:Rogam (anti-Rh Ab given during labor)

1. Isotypes

2. Allotypes3. Idiotypes

1. Are defined by antigenic (amino acid) differences in their constant regions Ig classes are different isotypes their H chains are antigenically different (all variants presentin serum)2. Antigenic features of Igs that vary among individuals


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B/c individuals have different alleles for L and H chains3. Antigenic determinants formed by specific amino acids in hypervariable region, thus specificto each Ig molecule Each is unique for the Ig produced by a specific clone of Ab producing cells Anti-idiotype Ab reacts only w/hypervariable region of Ig that induced it

Immunoglobulin classes

1. IgG (75%) monomer, H chain symbol = gamma

2. IgA (15%) monomer or dimer, H chain symbol = alphaSecretory IgA prevents attachment of microbes to mucous membran3. IgM (9%) monomer or pentamer, H chain symbol = mu

4. IgD uncertain function. On B cell surface. H chain = delta5. IgE monomer, H chain symbol = eta

1. L chains (light chains)2. H chains (heavy chains)

1. Belong to one of two types, k (kappa) or l (lambda) Both types occur in all classes of Igs, but only one Ig molecule contains only one type of Lchain Amino-terminal portion of each L chain participates in antigen-binding sites2. Distinct for each of the five Ig classes

Designated g, a, m, e, and d Amino terminal portion of each H chain participates in antigen-binding site Carboxy terminal forms the Fc fragment

How many domains do the H chains have in each of the 5 classes of immunoglobulin?

What do unique sequences in the H chains allow for?

1. IgG, IgA, and IgD H chains have 3 constant domains2. IgM and IgE H chains have 4 constant domains3. All L chains (both kappa and lambda) have 1 constant domain

Unique sequences in the H domains allow for isotypic variation (common to all members of thespecies), allotypic variation (variation between members of the species), complement binding, Fc

binding, and disulfide bond formation.


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Domain positions in IgG

1. Domains are loops of peptide stabilized by intra-chain disulfide bridges2. Each light chain has 1 variable and 1 constant domain VL and CL

3. Each heavy chain has 1 variable and 3 constant domains VH, CH1, CH2, and CH34. Remember: each heavy chain is identical to the other heavy chain in the immunoglobulinmolecule, same w/light chain5. Antigen binds to variable regions6. Each IgG molecule is bivalent, i.e., it has two identical binding sites for antigens

Fab and Fc positions

1. Fab Portion of IgG that binds the antigen Composed of entire light chain and the variable and 1st constant domain of heavy chain (VL,CL, VH, and CH1)2. Fc Terminal end of heavy chain (carboxy end) Controls the biological activity Contain amino acid regions that confer function such as complement activation and binding toFc receptors Ex. amino acid sequence Glu-Lys-Lys in Cg2 domain of IgG is needed for C1q of complementto bind to IgG

Hypervariable regions

1. Amino acid sequences in the variable domains of H and L that are unique from one Ig to thenext2. Called complementarity determining regions (CDRs)3. There are 3 CDRs in each H and L chain4. Where the antibody makes actual contact with the antigen5. Amino acid residues of antigen epitope form noncovalent bonds w/amino acids lining the

binding site on the Ab These weak noncovalent forces become stronger as the fit between Ag epitope and combiningsite _ 6. These variations are called idiotypic variations b/c they vary w/in a single member of a species7. Every human serum contains Igs of many different idiotypes


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CDRs and affinity and specificity

The better the antigenic epitope fits into Ab binding cleft (i.e. high specificity), the # andstrengths of the bonds _

_ association = _ affinity constant (K) = _ binding strength Specificity is relative in that binding clefts can accommodate cross-reacting antigenic epitopes Inject multivalent antigen into an animal antiserum containing Abs of multiple specificities &affinities Affinity and specificity mature w/time after immunization

1. Allotypic markers

2. Immune clearance

1. Additional antigenic features of Igs that vary among individuals (their biological function is

unknown) Are found in the: Fc portion of the H chain Constant portion of the L chain

2. Phenomenon where, generally, Ab-Ag binding facilitates the binding of Ab to Fc receptors on phagocytic cells

IgM Structure

1. Pentameric J chain links five subunits/chains of Ig together resulting in a pentamer 2. Has 20 chains and conceivably can bind to 10 antigens3. Only one is needed to activate complement system b/c it comes pre-packaged w/2 Fc receptorsclose to each other

Secretory IgA structure

1. Dimer J chain connects 2 Igs together

2. Also has a secretory piece thats added to help protect from proteolytic digestion which it getsinto secretions3. Note: secretory piece is NOT present on serum IgA


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IgG

1. Consists of 2 L chains and 2 H chains linked by disulfide bonds (divalent)2. Four subclasses

3. Directed against polysaccharide antigens4. Important defense against encapsulated bacteria5. Predominant Ab in secondary response6. Only antibody to cross placenta most abundant Igs in newborns7. Opsonizes (ie, enhance phagocytosis)8. Neutralizes virus or toxin upon binding to it

IgA

1. Main immunoglobulin in secretions (colostrum, saliva, tears, respiratory, intestinal and genital

tract secretions)2. Prevents attachment of bacteria and viruses to mucous membranes3. Each molecule consists of two H2L2 units + J chain and secretory component Secretory component polypeptide made by epithelium Provides for IgA passage to mucosal surface Also protects IgA from being degraded in intestinal tract4. Neutralizes toxin or virus upon binding to them

IgM

1. Two forms created via alternative mRNA splicing:

Secreted: main Ig produced early in primary response Membrane bound: on surface of B cells where it functions as an antigen-binding receptor (BCR) Accessory proteins a/b activate src-family tyrosine kinases Signals differentiation to plasma & memory cells2. BCR is a monomer 3. In serum, it is a pentamer (5 H2L2 units + J chain)4. Has 10 Ag-binding sites (highest avidity) most efficient Ig in agglutination, compementfixation, & other rxn5. Imp in defense against bacteria and viruses

IgD

1. Has no known Ab function2. May function as an antigen receptor since it is present on surface of many B cells3. Present in small amounts in serum


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IgE

1. Mediates immediate (anaphylactic) hypersensitivity2. Participates in host defenses against certain parasites (eg, helminths)3. Its Fc region binds to surface of mast cells and basophils

4. Bound IgE serves as a receptor for antigen (allergy) This An-Ab complex triggers allergic responses of the immediate (anaphylactic) type thrurelease of mediators5. Present in trace amounts in normal serum6. Persons w/allergic reactivity have __ amounts7. May appear in external secretions

Fc Receptors

1. Fcg receptors on phagocytes

Bind immune complexes promote phagocytosis On Tc and NK cells regulate ADCC On trophoblast and endothelial cells of placenta transport IgG into fetal circulation2. Fce receptors on mast cells Bind IgE triggers degranulation and allergy3. Fca receptors on basal surface of intestine epithelium Bind dimeric IgA promote transport of complex thru cell to gut lumen Portion is cleaved & remains w/IgA as secretory piece

1. How many gene segments code for V region of L chains?

2. How many gene segments code for V region of H chains?3. What does antibody diversity depend upon?4. In the synthesis of the H chain, what two segments are expressed first (and are present in the

primary RNA transcript)?

1. 2 gene segments (V + J) V codes for first 95 residues J codes for 13 residues2. 3 gene segments (V + D + J)3. a) Multiple gene segments for Variable regions

b) their rearrangement into different sequencesc) combining different L and H chains in assembly of Igsd) mutations (responsible for affinity maturation)4. Mu (m) and delta (d) (IgM and IgD H chains) Delta lacks a switch region, thus comes along for the ride with mu Two H chains produced will either have mu or delta


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Class Switching

1. Initially all B cells carry IgM specific for an antigen2. Later, gene rearrangement permits elaboration of Abs of same antigenic specificity but of different Ig classes

3. Occurs ONLY with HEAVY CHAINS4. Same VH (variable H) gene can associate with different CH (constant H) genes so that Igs produced later (IgG, IgA or IgE) are specific for same antigen as original IgM5. A different mechanism is used in switch from IgM to IgD A single mRNA is transcribed --> IgM & IgD mRNAs Thus mature B cells can express both IgM and IgD6. Note: once B cell has switched pass a certain H-chain gene, it can no longer make it b/cintervening DNA is discarded

1. How are cytokines involved in class switching?2. Generation of TCR diversity

1. IL-4 increases IgE, IL-5 (from T cells) increases IgA2. Ag binding portion of TCR is generated by 4 sets of genes: alpha and beta (on majority of Tcells), & gamma and delta (expressed on subpop of T cells) General arrangement of TCR genes similar to H chains Diversity is generated by: Multiple germ-line genes VJ and VJD recombination Joining site variation Multiple D region N-region diversification (random base inserts)

NO somatic mutations for T cell diversityHyper IgM immunodeficiency

1. X-linked trait, CD40 gene mutation2. Interaction of the CD40 protein on B cell with CD40 ligand protein on the Th cell is acontroller of class switching3. Failure of this interaction to occur results in an inability of the B cell to switch to productionof either IgG, IgA or IgE4. Therefore, only IgM is made5. Patient presents with: _ IgM, _ IgG Normal numbers of T cells and B cells Recurrent pyogenic infections (b/c these require IgG)6. Treat with passive immunotherapy IV gamma globulin from a pool of donors


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Functions of the complement system

- cytolysis complement binds to Ag-Ab complex and directs lysis of certain cell types; onlycertain bacteria are susceptible to lysis, also happens to some body cells (RBCs)- opsonization certain phagocytic cells that have complement receptors will recognize the

complement-Ab complex and opsonize the antigen- inflammation in the cascade, there are products of the complement system being producedcalled anaphylatoxins. These products have two roles:- recruit inflammatory cells to the area- activate these cells to produce mediators that will lead to additional inflammation. This willhelp in Ag clearance

Two Limbs of the Complement System Classical and Alternate

- similarities- both consist of inactive proteins -- zymogens

- both are highly regulated there are regulatory proteins at every step in the process- both involve enzymatic cascades- both end with the membrane attack complex (MAC)- difference is in how they are initiated- the classical system starts with antigen-antibody complex- the alternative system doesnt need antibody to start- alternative system used by Gram- and Gram+ bacteria, fungal & yeast cell walls, tumors,

parasites, etc.

1. Which antibodies are involved in the complement system?

2. How does C1 travel in the body and how/where/when does it bind to Ab-Ag complex?3. What produces complement components?

1. IgM and IgG ONLY C1 must bind to 2 Fc regions for cascade to occur IgM much more efficient for b/c only need 1 IgM as opposed to 2 IgGs (to actually have 2 IgGsclose enough for C1 to bind both requires at least 1000 IgG molecules)2. C1 travels in circulation bound to an inhibitor when it sees Ag-Ab, inhibitor is cleaved off and C1q component of C1 is able to bind to Fc

portion of Ab Then the cascading starts3. Hepatocytes and mononuclear phagocytes


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Alternate pathway

1. Spontaneous activation (autolysis) of C3 into C3a and C3b this process is called tickover2. C3b then binds to the cell membrane by itself When C3b binds to self cells _ inactivated

When C3b binds to foreign cells _ it sticks3. Binding of C3b leads to activation of other components4. Factor B interacts w/C3b _ proteolyzed by factor D to form C3bBb (C3 convertase) (differentfrom classical path)5. C3 convertase then activates another C3 to form C3b6. C3b combines with C3 convertase to form C3bBb3b (C5 convertase) (also different from onein classical path)7. C5 convertase then interacts w/C6, 7, 8 and 9 to form MAC

Control of the Classical Pathway

1. Time complement components need to be under fine control, dont want too much firingleading to constant inflammation (unbound components active for nanosec)2. Receptors different CRs on different cells CR1 B cells, PMNs, monocytes, macrophages CR2 B cells, dendritic cells CR3 monocytes, macrophages, PMNs, NK cells CR4 PMNs, monocytes, macrophages3. Specific factors regulatory factors that have very specific actions in limiting the complementsystem Ex: CCP and DAF inhibit C3 convertase MCP degrades C4b

What would a deficiency of the following result in:1. Early complement components (Clq, r, s OR C4 OR C2)2. Late components3. Regulatory factors4. Complement receptors

1. Still can kill microbes via alternative pathway but Chronic pyogenic infect. (they need to be phagocytized) Immune complex disease: Failure to clear Ag-Ab complexes _ vasculitis, glomerulonephritis2. Chronic Neisseria infections3. C1H (C1 inhibitor) deficiency _ autosomal HANE Hereditary angioneurotic edema Overactive system leading to chronic inflammation. C1 is not inhibited _ decreased levels of C44. Leukocyte adhesion deficiency (LAD) Inflammatory cells cant come since they are missing a CR leading to pyogenic infections


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Examples of lab tests that are based on:1. Primary unions/interactions2. Secondary unions/interactions3. Tertiary unions/interactions

1. Immunoflourescence, ELISA, flow cytometry2. Precipitation (pptn), agglutination, RID3. Complement fixation test

1. Class I MHC proteins

2. Class II MHC proteins

1. Composed of a chain and b2-microglobulin non-covalently bound together Antigen binds to a portion 8 amino acids

b2-microglobulin gene is on chromosome 15 Present viral antigens2. Class II composed of a and b chain Antigen binds to alpha 1 group and beta 1 group 30 amino acids Both chains encoded for on same chromosome Present extrinsic antigens such as bacteria

1. What does innate CMI refer to?2. What does adaptive CMI refer to?

1. Depends on cellular and humoral elements of inflammation; does not involve T cells directly Sets up stage for adaptive immunity Includes chemotaxis, phagocytosis, acute phase proteins, and inflammatory mediators(histamine, serotonin, PAF, IL-8, C3a, C5a, bradykinin, PGs, leukotrienes, etc.)2. Depends on T helper and cytotoxic cell functions Note: cytotoxic effectors include CD8 T cells, NK cells and macrophages CD4 cells stimulated by antigen from APCs _ grow and proliferate _ cytokine secreting andmemory cells

Hashimotos thyroiditis

1. Diffuse infiltration of thyroid w/lymphocytes, resulting in diffuse goiter, destruction of parenchyma and hypothyroidism2. Presents w/painless swelling in neck forming over 2-3 years Pertinent findings: enlarged thyroid, T3, T4, and TSH normal; serum contains anti-thyroglobulin and anti-thyroid microsomal (Abs to thyroid tissue)3. Patient returned complaining of lethargy, slowness of movement, memory loss, and weightgain


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Pertinent findings: _ T3 and T4, _ TSH, anti-thyroid antibodies _ from first visit4. Etiology of disease is the production of Abs to thyroid Ags

Immune Regulation

1. Antibody dependent B cell suppresion Blocking antibody: high doses of Ig block binding of antigenic determinant (epitope) andmembrane Ig on B cells (ex. Rogam) Receptor cross linking: Low doses of Ab _ antigen cross-links B cells Fc receptors and itsantigen receptors Tyrosine phosphatase activate _ inhibits cell activation2. Regulation by immune complexes either augment or inhibit response Inhibition: Fc receptor of B cell cross links w/Ag receptor by Ag-Ab complex _ signals B cellto stop antibody production phase Augmentation: APC-bound Ab _ presentation of Ag to B cells

3. Anti-idiotypes can either suppress or enhance immune response Produced to either non-antigen binding sites (paratopes) or to antigen binding sites (idiotopes)4. Immune repertoire MHC and non-MHC genes polymorphisms

Tumor specific antigens (TSAs)

1. Unique to cancer cells2. Not found on normal counterparts3. Arise through point mutations4. Unique to a single neoplasm arise through point mutations in DNA damaged by carcinogenic

chemicals, UV or X radiation, viral infections: hep B human T cell leukemia virus HPV _ cervical cancer Epstein Barr _ Burketts lymphoma

Tumor associated antigens (TAAs)

1. More often found on tumors rather than TSAs2. Found on both normal and malignant cells, but their expression is increased on tumor cells

3. Examples CEA (carcinoembryonic antigen) _ predictor of recurrence of colon cancer (200 ng/ml) (levels _ when cancer is present and drops when it is removed) Also used as prognosticator for metastasis Normal level: ~10ng/ml AFP (alpha feto protein) _ elevated in liver and testicular cancer (not absolute, can be raised incirrhosis and COPD) (very suspicious if >500ng/ml)


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Immune response to tumors

1. Humoral IgG & IgM Abs that fix complement destroy soft tumors Abs against tumors impede adhesion some tumors need

IgG Ab may mediate destruction of tumors via ADCC2. CMI _ MOST IMPORTANT mechanism (esp Tc cells) Macrophages activated by T cell derived IFN gamma kill tumor cells (TNFa, lysozyme, O2radicals) NK cells kill tumors by same mechanism they use to kill virus infected cells (cell w/_MHC _ signals NK) Tc kill tumors in Ag specific & MHC restricted way CMI is so imp b/c antigens made by tumors are processed by the endogenous pathway

Presentation of tumor antigen to immune system

Can occur in one of three ways:1. MHC I+ but B7 expressing tumor cell encounters Tc cell Results in anergy b/c need B7 to activate Tc cells Mechanism by which tumors evade immune response2. MHC I+ and B7+ expressing tumor cell encounters Tc cell Results in Tc activation3. APC present processed tumor Ag to Th cells Tumor cell sheds antigen _ APC phagocytizes & presents Ag to Th cell _ Th cell activates &secretes cytokines _ Tc cell activated _ Tc destroys tumor cell NOTE: Tumor cells DO NOT express MHC II, so they rely on APCs to get Th cell response

Mechanisms tumors use to evade the immune response

1. Lack of co-stimulatory molecule (B7) on tumor cells Most tumor cells are poor APCs since they lack B7 May also lack adhesion molecules (LFA-3, ICAM-1) Some show a _ or complete loss of MHC I _ prevents tumor recognition by Tc cells (though itattracts NK)2. Block antibodies Ab + shed tumor Ag complexes can saturate Fc receptors on macrophages, neutrophils, NK andTc cells Prevents these effectors from interacting w/tumor cells3. Secretion of suppressive factors TGF beta, prostaglandin E2 _ inhibit T cells Mucin _ anti-adhesive molecule


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Cancer immunotherapy

1. Anti-Cancer vaccines Immunization against oncogenic viruses More difficult to vaccinate against non-viral origins, ex:

BCG (enhances responses against melanoma) Transfection of genes for B7, IL-2, IL-4, IFN gamma, GM-CSF (_ response of T cells) Naked DNA constructs (induces Tc cell)2. In vitro activation of LAK cells & TIL (tumor infiltrating lymphocytes) with IL-23. Monoclonal antibodies (Mabs) made w/mice spleens Problem: HAMA response (human anti-mouse Ab response); Solution: chimeric Mabs

1. Heteroconjugate Mabs2. Chimeric Mabs

1. Bi-specific Mabs that have 2 Fab regions: One against CD marker (ex. CD16 _ NK marker) One against tumor Ag2. Mabs made up of: Human constant region Murine VL and VH regions Show a decreased HAMA response Humanised Ab _ advanced chimeric Ab Herceptin _ humanised Ab in metastatic breast CA Binds HER-2/neu, growth factor rec.on tumor cells

Only Mab shown to be effective

Cytokine therapy for tumors

1. IFN alpha Remission in hairy cell leukemia pts Possible cytostatic effect on tumor 2. IFN gamma Ineffective systemically, remission of ovarian CA _ expression of MHC class I, cytostasis3. IL-2 Remissions in renal cancer and melanoma T cell activation and proliferation, NK cell activation4. TNF alpha Can _ malignant ascites Macrophage & lymphocyte activation


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1. Innate immunity to bacteria2. Adaptive immunity to bacteria

1. Various bacteria contain antigens in their cell envelopes and walls ranging from LPS to

lipoarabino-mannan Antigens interact w/serum factors & cells _ inflammat, influx of complement, phagocytes,cytokines (IL-12) Bacteria killed primarily by degradation in phagocytes Accomplished by both O2-dep and O2-indep killing2. Antibodies play imp role in resistance to bacteria Bind to bacteria _ prevent attachment to host, activate phagocytosis & complement, preventnutrient transport Also neutralize toxins released from bacteria CMI (T cells and macrophages) important in fighting intracellular bacteria

Describe the innate pathway triggered by bacteria.

1. Acute phase proteins bind to CHO moieties on bacterial surface _ alter complement pathway _ C3a, C5a _ vascular permeability, chemotaxis, etc.2. Formyl peptide, muramyl peptide, peptidoglycan, Lipoproteins, lipoteichoic acid, LPS,lipoarabinomannan Break down products of bacterial cell wall Activate NK cells, macrophages and PMNs, 2)interact w/blood clotting, platelet, plasminsystem In ALL bacteria

Specific for gram-positive bacteria Specific for gram-negative bacteria Specific for acid-fast bacteria

Describe adaptive immunity mechanisms against bacteria.

1. Antibodies esp imp for extracellular bacteria: Fimbriae, lipoteichoic acids BLOCK attachment Transport mech., receptors BLOCK proliferation Also ENHANCE phagocytosis Envelope Ag., Fc and C3 receptors ENHANCE lysis Toxins BLOCK toxic effects2. CMI to bacteria especially imp for intracellular bacteria: Ex of intracell bacteria: M. tuberculosis, Salmonella typhi, Legionelle pneumophils, Listeriamonocytoge, Chlamydia p., Brucella Immune system recognizes infected macrophage _ Th1 cells secrete IFNg and TNF _ macrophage activated _ kills bacterium


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Innate immunity to viruses

1. IFN _ produced by macrophages, T & other immune cells IFNg (immune) _ potent activator of APCs, Tc & NKs Also _ expression of MHC class II

IFNa & b (non-immune) _ inhibit viral replication by inducing kinases that phosphorylatetranslation factors (eIF-2) _ inhibits initiation of translation All _ expression of MHC 1 and B2 microglobulin2. NK cells Important first line of defense, killing infected cells that are still low in MHC antigens Big producers of IFNs besides being activated by them

Adaptive immunity to viruses

1. Virus specific Abs can: Prevent infection by neutralizing virus (before attaches)

Damage virus envelope by binding to virus and activating complement Promote viral-infected cell lysis (by complement, phagocytosis, and ADCC)2. IgA in secretions _ protect mucosa-penetrating virus3. CD8+ T cells _ main defense against virus infected cells Viral proteins associate w/MHC class I If __ _ virus becomes chronic and spreads4. CD4+cells secrete cytokines(IFN,TNF)_activate phagocytes, provide setting for Tc cells tokill target

Parasitic infection

1. 2 types: 1-celled protozoa, macroscopic metazoan/worms2. Can exist either in cells or extracellularly3. Generally: Ab best for extracell., CMI best for intracellular 4. Innate immunity to parasites: Phagocytic cells ingest small parasites Eosinophils _ resistance to worm infections Combine w/IgE & mast cells to provide resistance Activated by cytokines, kill by O2 dep & indep mechanisms5. Adaptive immunity to parasites: CD8+ cells imp in killing cells parasitized by protozoa Th1 and Th2 also important: Th2 induces IgE, eosinophilia & mast cells Th1 enhances CMI


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Infectious mononucleosis

1. Presents w/malaise, sore throat, fever, headache, red throat, exudative tonsils, tender lymphnodes2. Monospot test positive

3. WBCs show lymphocytosis with atypical cells (T cells)4. Virus infects epithelium of pharynx, producing sore throat5. B cells then become infected: Epstein-Barr virus docks to CR2 on B cells, fibroblasts, andepithelial cells Stimulates B cells to make polyclonal Abs (heterophile Abs), detected by the monospot test6. So remember: The monospot response is the B cell response The atypical lymphocyte is the T cell

1. Passive immunity2. Active immunity

1. Immediate immunity but transient Giving person preformed antibody Ex. hyperimmune Ig after infection or snake bite Ex. Passive transfer of Ig from mother to child2. Delayed immunity but more permanent Ex. natural exposures to antigens in pathogens Ex. vaccines

Types of vaccines

1. Killed organism (ex Salk polio vaccine)2. Ag part of disease causing organism (ex H. influenzae) Called acellular3. Attenuated or weakened preparation (polio, measles)4. Toxoid vaccines Toxins treated w/or absorbed w/aluminum salts Usually must add an adjuvant to _ immunogenicity Ex. diptheria & tetanus toxoids combined w/ pertussis (adjuvant)5. Organism similar to virulent one (Jenner cowpox, BCG for TB)6. Subunit vaccines (ex hep B) Genetically engineered7. DNA plasmid vaccines Mimics live attenuated vaccine preps

Ways to give vaccines

1. Parenteral route (not po) _ mainly elicits IgG antibodies SubQ IM


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ID (intradermal)2. Oral route _ mainly elicits IgA antibodies due to GALT

1. Live attenuated vaccines2. Killed vaccines

3. Vaccines based on subcellular microbial fragments

1. Polio, mumps, measles, rubella, yellow fever, varicella zoster, hepatitis A, TB2. Very effective: Polio (salk) and rabies Moderately effective: Typhoid, cholera, influenza Debatable: Plague Controversial on basis of toxicity: Pertussis (cellular) acellular pertussis vaccine that is lesstoxic is now used3. Haemophilus influenza, hepatitis B virus

Recommended childhood immunization schedule

1. Birth _ Hep B12. 1 4 months _ DTaP (diptheria, tetanus, acellular pertussis), Hep B2, and Polio3. 6 18 months _ Hep B3, Hib (H. influenza type B), Polio, MMR (measles, mumps, rubella),Var (V. zoster), HepA4. 11-2 years _ tetanus (tetanus should be given every 10 yrs)

Adjuvants

1. Agents given with vaccines to enhance their immunogenicity

2. Mechanism: Depot effect (concentrate Ag in a particular area) Increase particle size of an antigen Increase release of cytokines3. Examples: Inorganic salts (Aluminum OH, Aluminum PO4) Delivery systems (liposomes, BCG) Bacterial products (Freunds adjuvant) Causes inflammatory granuloma response that increases immunogenicity

Non-specific immunotherapy

1. Microbial Filtered bacterial cultures: Coleys preparation BCG: anti-tumor activity2. Cytokines IFNgamma: leprosy, leishmaniasis IL-2: leishmaniasis GCSF: bone marrow restoration


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BCG: anti-tumor activity3. Cytokine inhibitors TNF antagonists: septic shock

Hypersensitivity reaction: Type I(i.e. immediate or anaphylactic hypersensitivity)

1. Occurs when antigen binds to IgE on surface of mast cell IgE binds by its Fc portion to basophils and mast cells Reexposure to same antigen results in cross-linking of cell-bound IgE and release of activemediators2. Immediate response _ Wheel and Flare Wheel is result of histamine release Flare is result of 3. Late response (@ 5 hrs) _ lumps form (induration of cells)

4. Ex: Sea food, nuts, bees, wasps, hornets, ants, penicillin5. Which clinical manifestation occurs depends on location of mast cells bearing IgE specific for allergen6. Most severe = systemic anaphylaxis (bronchocons., shock)

What are the active mediators released by mast cells in Type I hypersensitivity?

1. Histamine (preformed) Cause vasodilation, _ capillary permeability, smooth-muscle contraction

Causes allergic rhinitis, urticaria, and angioedema Contributes to bronchospasms in acute anaphylaxis2. SRS-A _ leukotrienes (NOT preformed) Cause _ vascular permeability, smooth-mus contraction Principle mediators in bronchoconstriction of asthma3. Eosinophil chemotactic factor A/ECF-A (preformed)4. Prostaglandins and thromboxanes (NOT preformed) Cause dilation, _ vascular perm., bronchoconstriction Aggregate platelets

Type II hypersensitivity (cytotoxic)

1. Mediated by mainly IgG, but also IgM2. Occurs when Ab directed at antigens of cell membrane activates complement _ MAC _ celllysis Macrophages also activated _ IL-1, TNF _ fever, etc.3. Can occur with autoAbs or altered self (eg due to virus)4. Examples:


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Hemolytic disease of newborn (Rh reactions) Goodpastures syndrome: IgG Abs to glomerular BM Result: nephritis, proteinuria Lung also damaged b/c of similarities of BM Pemphigus: Abs to desmosome proteins

Breakdown of cellular adhesions _ blistering

Type III Hypersensitivity

1. Mediated by immune complexes (IgG)2. Antigen-antibody complexes are deposited in tissues Activates complement _ C3a, C5a PMNs to site_release lysosome enzyme_tissue damage Cytokines produced _ TNFa, IL-1 Direct action on basophils and platelets

3. Arthus rxn (local inflammation)4. Serum sickness (systemic inflammatory response) Results in fever, urticaria, arthralgia, lymphadenopathy, and eosinophilia days - 2 weeks after injection Acute: 1large dose _ vasculitis, nephritis, arthritis Chronic: multiple injections _ kidney, arterial, and lung damage Ex. rheumatoid arthritis, Lupus

Type IV Hypersensitivity (delayed)

1. T cell mediated (only type NOT humorally related)2. Can be caused by: CD8+ Tc cells attack skin cells (poison oak allergy) CD4+ Th cells sensitized _ lymphokines (TB skin test)3. Contact hypersensitivity (12-72 hrs post-exposure) Occurs w/chemicals, plants, topical drugs, soaps, etc. Ex nickel, formaldehyde, poison ivy & oak, neomycin Act as haptens _ skin _ attach to body proteins _ complete Ag Result: erythema, itching, vesicles, or necrosis of skin4. Tuberculin-Type (48-72 hrs post-exposure) Local induration (lymphocytes, macrophages)5. Granuloma Type (21-28 days post-exposure) Ex. leprosy, TB, fungal infections

Patterns of infection

1. Humoral immunodeficiency most common X-linked hypogammaglobulinemia (Brutons Agamma.)


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IgA deficiency Common variable immunodeficiency2. Combined B Cell & T Cell deficiencies Severe combined immunodeficiency disease (SCID) Ataxia telangiectasia

Wiskott-Aldrich syndrome3. T-cell immunodeficiency Thymic aplasia (DiGeorges syndrome) Chronic mucocutaneous candidiasis4. Neutrophil/granulocyte immunodeficiency (rare) Leukocyte adhesion defect Chronic granulomatous disease Chediak-Higashi syndrome Jobs syndrome (Hyper IgE syndrome)5. Complement deficiency (rare) early and late deficiencies

What is the pattern of:1. humoral immunodeficiencies?2. Cellular (T lymphocyte) immunodeficiencies?3. Neutrophil/phagocyte/granulocyte immunodeficiency?4. Complement defects?

1. Recurrent sinopulmonary infections NOT a cold! sinusitis, pneumonia, otitis media, high grade pathogens _ occurrence of arthritis, autoimmune disease, viral gastroenteritis2. Recurrent Opportunistic infections

LOW grade path (pneumocystisis, fungi, multi-dermatomal zoster) Generally affect kids, but most common in HIV pts _ incidence of various malignancies, esp lymphomas3. Soft tissue bacterial infections Gingivitis, lymphadenitis, osteomyelitis, pulmonary cool abscesses ~ always by 2 yrs, often from birth w/delayed separation of umbilical cord Typically infected w/low grade pathogens OR catalase + organisms (staph, strep, pseudomonas,E. coli, candida, aspergillus)4. Depends on complement (C) component defect: Early C defects _ respiratory infections, recurrent colds Late C defects _ gram- infections (recurrent meningitis)

X-linked Hypogammaglobulinemia (Brutons Agammaglobulinemia)

1. Congenital B cell deficiency2. B cells dont develop, atypical lymph node structure w/o germinal centers or plasma cells3. Very low serum Igs of all isotypes4. Most common defect is in Brutons tyrosine kinase/Btk Required for maturation of pre-B cells to mature B-cells


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Seems to be imp for Ig light chain synthesis5. Diagnosis: serum protein electrophoresis to exclude lymphoid/plasma cell malignancy,quantitative Ig isotypes, flow cytometry using B cell markers (CD19 or CD20)6. Treatment: g-globulin replacement (IV every 3-4 weeks) Antibiotic therapy of sinopulmonary infections

IgA deficiency

1. Most common congenital humoral immunodeficiency 1:700 of Caucasians from northern Europe background2. Does NOT always cause disease (may be subclinical)3. Variable inheritance w/autosomal dominant or recessive4. May lead to common variable immunodeficiency5. Clinical severity HIGHLY variable (many asymptomatic)6. Others have serious, recurrent sinopulmonary and GI infections

7. B-lymphocyte number is NORMAL8. LOW IgA9. Same treatment as Brutons

Common variable immunodeficiency

1. Variable autosomal genetic mechanism, but develops in late childhood to early adult life (thusan acquired ID)2. Hyperplastic lymph nodes w/normal to increased numbers of B-cells but decrease in plasma

cells3. Increase in lymphoid and GI malignancies as well as autoimmune diseases4. VERY low IgG, low to NO IgA5. Same treatment as Brutons

SCID

1. Heterogenous group of disorders w/defective development of both B- and T- cells, usually dueto abnormal development of bone marrow cells2. In some forms, abnormal B-cells is secondary to dysregulation of abnormal T-cells

3. Thymus and peripheral lymph nodes do not develop4. Affected pts usually die of infections w/in 1st year of life if condition is not recognized5. Deficiency in IL-2 receptor for gamma chain6. Cant respond to IL-2, IL-4, IL-77. Treatment: bone marrow transplant (cure if successful)

1. Ataxia telangiectasia


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2. Wiskott-Aldrich3. Mucocutaneous candidiasis

1. Aut recessive, mutation in DNA repair genes

Child starts to walk, but then regresses (gets ataxic) @ 14-16 months, end up in wheelchair byage 7-10 Then develop telangiectasia of lateral aspect of eye Lymphopenia and IgA deficiency commonly occur 2. X-linked disease of T cell defect Recurrent pyogenic infections, eczema in weird places3. Severe form of candida that spreads everywhere T cell defect where T cells dont see candida Treatment: antifungals Survive to adulthood

DiGeorge Syndrome

1. Congenital defect of T cells of variable severity2. Malformation of 3rd and 4th branchial clefts3. Manifestations include: Thymic aplasia w/deficiency of T-cell development Absent parathyroids w/hypocalcemia Abnormality of great vessels connected to heart Facial deformities (wide set eyes, low set ears, funny looking kid/FLK)4. Associated w/maternal alcohol ingestion, autosomal dominant inheritance, translocation of chromosome 22

5. May improve w/time, probably due to partial thymic function or substitution of other lymphtissue for thymus

Chronic granulomatous disease

1. Recurrent soft tissue abscesses2. Rare disorder affecting 1:1,000,000 (2/3 are X-linked)3. Recurrent bacterial and fungal infection (often w/organisms that are catalase positive), oftenw/formation of granulomas4. X-linked: defect in production of superoxide b/c of: Cytochrome b558 defect _ impaired NADPH oxidase5. Autosomal: defect in other components of NAPDH oxidase6. Diagnosis: CBC Nitroblue tetrazolium test or chemiluminescence to assess production of O2 radicals (dyereduces to dark color by oxidation)7. Treatment: IFNg


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Leukocyte adhesion defect

1. Extremely rare2. Umbilical cords dont separate, still present @6 months b/c neutrophils cant go into that areato lyse collagen to break it off

3. High white count (b/c neutrophils are staying in the blood and cant find their way out)4. Measure CD18 adhesion molecule to diagnose Absent in these pts

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