Section ISection I

ImmunologyImmunology

Nonspecific Mechanisms To Nonspecific Mechanisms To Fight InfectionFight Infection

Skin & Mucous MembranesSkin & Mucous Membranes– Sweat gland secretions (acidic)Sweat gland secretions (acidic)– Bacterial flora release acidsBacterial flora release acids– Saliva, tears and mucous secretionSaliva, tears and mucous secretion– Lysozyme in tears and perspirationLysozyme in tears and perspiration– Nostril hairsNostril hairs– Stomach acidStomach acid

Phagocytic Phagocytic White CellsWhite Cells and and Natural Killer CellsNatural Killer Cells

Neutrophils ( majority of wbc’s)Neutrophils ( majority of wbc’s)

- Released from bone marrow- Released from bone marrow– Enter by amoeboid mov’t; live only a few daysEnter by amoeboid mov’t; live only a few days– Attracted by a chemical signal (i.e., pus)Attracted by a chemical signal (i.e., pus)– Capable of phagocytosis Capable of phagocytosis

or cell lysis (engulf)or cell lysis (engulf)– Arrive first, eliminate Arrive first, eliminate

microorganisms & diemicroorganisms & die

Phagocyte ingesting polystyrene Phagocyte ingesting polystyrene beadsbeads

These phagosomes These phagosomes deliver their contents deliver their contents to lysosomesto lysosomes

Phagocytic Phagocytic White CellsWhite Cells and and Natural Killer Cells (cont.)Natural Killer Cells (cont.)

MonocytesMonocytes migrate to the tissues (organ & migrate to the tissues (organ & connective) where they enlarge and become connective) where they enlarge and become macrophagesmacrophages– From bone marrowFrom bone marrow– Use pseudopodia to phagocytize cells (e.g. Use pseudopodia to phagocytize cells (e.g.

bacteria, viruses, & cell debris)bacteria, viruses, & cell debris)– Secrete lysozyme and interferonSecrete lysozyme and interferon– Expose molecules of digested bodies to more Expose molecules of digested bodies to more

specialized calls, such as B and Th lymphocytesspecialized calls, such as B and Th lymphocytes

Phagocytic Phagocytic White CellsWhite Cells (cont.) (cont.)

Eosinophils: Eosinophils: Understanding The Immune System - PhaUnderstanding The Immune System - Phagocytes and Granulocytesgocytes and Granulocytes

– Have digestive enzymes in granules which Have digestive enzymes in granules which are discharged against pathogen or parasitic are discharged against pathogen or parasitic worms and Phagocyte antigen - antibody worms and Phagocyte antigen - antibody complexes complexes

Cells within the tissues of the Cells within the tissues of the Immune SystemImmune System

Natural Killer Cells or NKNatural Killer Cells or NK

To attack, cytotoxic T cells need to To attack, cytotoxic T cells need to recognize a specific antigen, recognize a specific antigen, whereas natural killer or NK cells whereas natural killer or NK cells do not. Both types contain do not. Both types contain granules filled with potentgranules filled with potentchemicals, and both types chemicals, and both types kill on contact. The killer binds kill on contact. The killer binds to its target, aims its weapons, to its target, aims its weapons, and delivers a burst of lethal chemicals.and delivers a burst of lethal chemicals.

Mature T cell & MacrophagesMature T cell & Macrophages

Bind to receptor onBind to receptor on

target cellstarget cells

Recruit other cellsRecruit other cells

Can serve as interleukinsCan serve as interleukins

in that they serve as a in that they serve as a

messenger between messenger between

leukocytes or wbc’sleukocytes or wbc’s

Antimicrobial ProteinsAntimicrobial Proteins

Complement SystemComplement System– ~ 20 proteins which interact~ 20 proteins which interact– Attract phagocytes (call Attract phagocytes (call chemotaxischemotaxis) to ) to

foreign cells and help destroy by promoting foreign cells and help destroy by promoting cell lysiscell lysis

Antimicrobial Proteins (cont.)Antimicrobial Proteins (cont.)InterferonsInterferons– Secreted & produced by virus-infected cellsSecreted & produced by virus-infected cells– Types: Types: alpha, beta, and gammaalpha, beta, and gamma– Stimulate production of proteins that inhibit viral replication Stimulate production of proteins that inhibit viral replication

(including neighboring cells)(including neighboring cells)– Not a virus-specific defenseNot a virus-specific defense– Works best against short-term infections such as colds and Works best against short-term infections such as colds and

influenzainfluenza– Activates phagocytes which enhances their ability to ingest Activates phagocytes which enhances their ability to ingest

and kill microorganismsand kill microorganisms– Can be mass produced to be tested as treatments for viral Can be mass produced to be tested as treatments for viral

infections and cancerinfections and cancer

Inflammatory ResponseInflammatory Response

Occurs when there is damage to tissue Occurs when there is damage to tissue due to physical injury or entry of due to physical injury or entry of microorganismmicroorganism

VasodilationVasodilation of small vessels increases of small vessels increases the blood supply to the area (redness)the blood supply to the area (redness)

Dilated vessels become more permeable, Dilated vessels become more permeable, allowing fluids to move in, resulting in a allowing fluids to move in, resulting in a localized localized edemaedema

Inflammatory Response (cont.)Inflammatory Response (cont.)Chemical signals initiate the inflammatory Chemical signals initiate the inflammatory responseresponse– HistamineHistamine released from cells called released from cells called BasophilsBasophils

and and mastmast cells in connective tissue cells in connective tissue– ProstaglandinsProstaglandins released from white blood cells and released from white blood cells and

damaged tissue (cause increased blood flow)damaged tissue (cause increased blood flow)– The increased blood flow delivers clotting elements The increased blood flow delivers clotting elements

which help block the spread of pathogenic which help block the spread of pathogenic microbes and begins the repair processmicrobes and begins the repair process

Inflammatory Response (cont.)Inflammatory Response (cont.)

Macrophages destroy pathogens and clean Macrophages destroy pathogens and clean up areaup area

Pus may develop before absorbed by the Pus may develop before absorbed by the bodybody

Bone marrow may release more leukocytesBone marrow may release more leukocytes

Fever develops due to toxins produced or Fever develops due to toxins produced or due to pyrogens released by leukocytesdue to pyrogens released by leukocytes– Fever can inhibit growth of some micro’sFever can inhibit growth of some micro’s

Complement SystemComplement System

These complement proteinsThese complement proteins

help the antibodies destroyhelp the antibodies destroy

bacteriabacteria

The diagram shows the C1The diagram shows the C1encountering an antibody boundencountering an antibody bound

to an antigento an antigen

The end product punctures theThe end product punctures the

cell membrane of the target cellcell membrane of the target cell

Complements illustratedComplements illustrated

Section IISection II

Immune System Defends the Immune System Defends the Body Against Specific Body Against Specific

InvadersInvaders

Antigen /Antibody ConnectionAntigen /Antibody Connection

Foreign molecules, or antigens, carry Foreign molecules, or antigens, carry distinctive markers, characteristic shapes distinctive markers, characteristic shapes called called epitopesepitopes that protrude from their surfaces. that protrude from their surfaces.

Our Immune system has the ability to Our Immune system has the ability to recognize many millions of distinctive recognize many millions of distinctive non-self molecules, and to respond by non-self molecules, and to respond by producing molecules, or antibodies producing molecules, or antibodies - also cells - that can match and counteract - also cells - that can match and counteract each one of the non-self molecules.each one of the non-self molecules.

Antigen/Antibody Continued (2)Antigen/Antibody Continued (2)

An An antigenantigen can becan be a bacterium or a virus, a bacterium or a virus, or even a portion or product of one of or even a portion or product of one of these organisms. Tissues or cells from these organisms. Tissues or cells from another individual also act as antigens; another individual also act as antigens; that's why transplanted tissues are that's why transplanted tissues are rejected as foreign.rejected as foreign.

How Antibodies are ProducedHow Antibodies are Produced

Third Line of DefenseThird Line of DefenseSpecificitySpecificity:: recognize and eliminate recognize and eliminate

microorganisms and foreign moleculesmicroorganisms and foreign molecules– Antigen:Antigen: foreign substances that elicit an foreign substances that elicit an

immune responseimmune responseCan be molecules exhibited on the surface of, produced by, Can be molecules exhibited on the surface of, produced by, or released from bacteria, viruses, fungi, protozoans, or released from bacteria, viruses, fungi, protozoans, parasitic worms, pollen, insect venom, transplanted organs, parasitic worms, pollen, insect venom, transplanted organs, or worn-out cellsor worn-out cells

Each has a unique molecular shapeEach has a unique molecular shape

Stimulates production of an antibody that defends Stimulates production of an antibody that defends specifically against the particular antigenspecifically against the particular antigen

Third Line of Defense (cont.)Third Line of Defense (cont.)

Antibody:Antibody: antigen-binding antigen-binding

immunoglobulin (protein), immunoglobulin (protein),

produced by B cells; produced by B cells;

functions as the functions as the effectoreffector

in an immune response.in an immune response.

Third Line of Defense Continued:Third Line of Defense Continued:

Diversity: Diversity: ability to respond to invaders ability to respond to invaders which are recognized by their antigenic which are recognized by their antigenic markersmarkers– Based on a variety of lymphocyte pop’sBased on a variety of lymphocyte pop’s– Each antibody-producing lymphocyte is Each antibody-producing lymphocyte is

stimulated by a specific antigen; lymphocytes stimulated by a specific antigen; lymphocytes synthesize and secrete the appropriate synthesize and secrete the appropriate antibodyantibody

Third Line of Defense (cont.)Third Line of Defense (cont.)Memory: Memory: your immune system can recognize your immune system can recognize previously encountered antigens and react fasterpreviously encountered antigens and react faster

Acquired immunity is a resistance to some infection Acquired immunity is a resistance to some infection encountered earlier in life (e.g. chicken pox)encountered earlier in life (e.g. chicken pox)

Self/nonself recognition:Self/nonself recognition: the ability to distinguish the ability to distinguish between the body’s own molecules versus foreign between the body’s own molecules versus foreign moleculesmolecules– Failure leads to autoimmune disorders which destroy Failure leads to autoimmune disorders which destroy

body’s own tissue body’s own tissue

Active Versus Passive Acquired Active Versus Passive Acquired ImmunityImmunity

Active Immunity:Active Immunity: conferred by recovery conferred by recovery from an infectious diseasefrom an infectious disease– Depends on each person’s immune systemDepends on each person’s immune system– Acquired naturally from an infection or artificially Acquired naturally from an infection or artificially

by vaccinationby vaccination– Vaccines can be inactivated bacterial toxins, Vaccines can be inactivated bacterial toxins,

killed microorganisms, or weakened living killed microorganisms, or weakened living microorganismsmicroorganisms

Can no longer cause the diseaseCan no longer cause the disease

Can act as antigens and stimulate immune responseCan act as antigens and stimulate immune response

Active Versus Passive Active Versus Passive Acquired Immunity (cont.)Acquired Immunity (cont.)

Passive immunityPassive immunity can be transferred from one person to can be transferred from one person to another by the transfer of antibodiesanother by the transfer of antibodies– Antibodies can cross the placenta to the fetusAntibodies can cross the placenta to the fetus– Some from nursing infants through milkSome from nursing infants through milk– Persists a few weeks or months until infant’s own system defends Persists a few weeks or months until infant’s own system defends

its bodyits body– Can be transferred artificially from an animal or human already Can be transferred artificially from an animal or human already

immune to the diseaseimmune to the diseaseRabies is treated by injecting antibodies from people vaccinated against Rabies is treated by injecting antibodies from people vaccinated against rabiesrabies

Short in duration, but permits your body to begin to produce antibodies Short in duration, but permits your body to begin to produce antibodies against the virusagainst the virus

Humoral Immunity and Cell-Humoral Immunity and Cell-Mediated ImmunityMediated Immunity

Humoral Immunity: Humoral Immunity: produces antibodies produces antibodies in response to toxins, free bacteria, and in response to toxins, free bacteria, and virusesviruses– Synthesized by certain lymphocytes and Synthesized by certain lymphocytes and

circulate in blood plasma and lymphcirculate in blood plasma and lymph

Cell-mediated Immunity:Cell-mediated Immunity: the response to the response to intracellular bacteria and viruses, fungi, intracellular bacteria and viruses, fungi, protozoans, worms, transplanted tissues, protozoans, worms, transplanted tissues, and cancerand cancer

Cells of the Immune SystemCells of the Immune System

LymphocytesLymphocytes– Responsible for both humoral and cell-mediated Responsible for both humoral and cell-mediated

immunity in that there are two main classes; B immunity in that there are two main classes; B cells and T cellscells and T cells

Develop from multipotent stem cells in bone marrow, Develop from multipotent stem cells in bone marrow, differentiate when they reach the site of maturationdifferentiate when they reach the site of maturation

B cells (B lymphocytes):B cells (B lymphocytes): the humoral immune and in the humoral immune and in the bone marrow until maturationthe bone marrow until maturation

T cells (T lymphocytes):T cells (T lymphocytes): the cell-mediated immune the cell-mediated immune response; migrate to the thymus gland to matureresponse; migrate to the thymus gland to mature

Types of cells: B CellsTypes of cells: B Cells

B cells (B lymphocytes):B cells (B lymphocytes): the humoral the humoral immune and in the bone marrow until immune and in the bone marrow until maturationmaturation

Cells of the Immune System Cells of the Immune System (cont.)(cont.)

– Mature cells (B and T) are concentrated in the Mature cells (B and T) are concentrated in the lymph nodes, spleen, and other lymphatic lymph nodes, spleen, and other lymphatic organsorgans

They are there to contact antigensThey are there to contact antigens

Antigen receptors are on the membranes of bothAntigen receptors are on the membranes of both

The receptors on a B cell are membrane-bound The receptors on a B cell are membrane-bound antibody molecules which will recognize specific antibody molecules which will recognize specific antigensantigens

The T cell antigen receptors are proteins (not The T cell antigen receptors are proteins (not antibodies) embedded in the membrane which antibodies) embedded in the membrane which recognize specific antigensrecognize specific antigens

Cells of the Immune System Cells of the Immune System (cont.)(cont.)

Effector CellsEffector Cells– Actually defend the body during an immune responseActually defend the body during an immune response– Result from a division of lymphocytes when the binding Result from a division of lymphocytes when the binding

of antigens to their antigen receptorsof antigens to their antigen receptors– Activated B’s give rise to effector cells called Activated B’s give rise to effector cells called plasma plasma

cellscells which secrete antibodies that eliminate the which secrete antibodies that eliminate the activating antigenactivating antigen

– Activated T cells produce two types:Activated T cells produce two types:Helper T cells:Helper T cells: secrete cytokines secrete cytokines

Cytotoxic T cells:Cytotoxic T cells: destroy infected and cancer cells destroy infected and cancer cells

Cells of the Immune System Cells of the Immune System (cont.)(cont.)

Helper T cellsHelper T cells::

secrete cytokines; carry thesecrete cytokines; carry the T4 markerT4 marker; essential ; essential for turning on antibody for turning on antibody production; activate production; activate cytotoxic T cells cytotoxic T cells

Cytotoxic T cellsCytotoxic T cells:: destroy cells infected by destroy cells infected by viruses or cancer; subset ofviruses or cancer; subset ofT cellsT cells

CytokinesCytokines

CytokineCytokine:: lymphokines can be lymphokines can be produced by lymphocytes & produced by lymphocytes & monokines by monocytes & monokines by monocytes & macrophagesmacrophages

Section IIISection III

Clonal Selection of Clonal Selection of Lymphocytes; Basis for Lymphocytes; Basis for

Immunological Specificity and Immunological Specificity and DiversityDiversity

Response Due to Diversity of Response Due to Diversity of Antigen-Specific LymphocytesAntigen-Specific Lymphocytes

Each lymphocyte will respond to only one Each lymphocyte will respond to only one antigenantigenDetermined during embryonic Determined during embryonic development before antigen are development before antigen are encounteredencounteredClonal SelectionClonal Selection – antigenic-specific – antigenic-specific selection of a lymphocyte that activates selection of a lymphocyte that activates clones of effector cells that eliminate the clones of effector cells that eliminate the antigen that provoked the initial immune antigen that provoked the initial immune responseresponse

Response Due to Diversity of Response Due to Diversity of Antigen-Specific Lymphocytes Antigen-Specific Lymphocytes

(cont.)(cont.)When an antigen enters the body, it binds to When an antigen enters the body, it binds to receptors on specific lymphocytes – those receptors on specific lymphocytes – those lymphocytes are activated and begin dividinglymphocytes are activated and begin dividing– These divisions make identical These divisions make identical effector cellseffector cells or or

clones that bind to the antigen that stimulated clones that bind to the antigen that stimulated the responsethe response

– e.g., a B cell when activated, will proliferate to e.g., a B cell when activated, will proliferate to make plasma cells that secrete an antibody make plasma cells that secrete an antibody which acts as a antigen receptor for the specific which acts as a antigen receptor for the specific antigen that activated the original B cellantigen that activated the original B cell

Section IVSection IV

Memory Cells Action in a Memory Cells Action in a Secondary Immune ResponseSecondary Immune Response

Primary Immune ResponsePrimary Immune Response

Primary Immune Response – the making Primary Immune Response – the making of lymphocytes to form clones of of lymphocytes to form clones of effector effector cellscells specific to antigen specific to antigen

5 to 10 day lag between exposure and 5 to 10 day lag between exposure and effector cellseffector cells

Lymphocytes to effector T cells & plasma Lymphocytes to effector T cells & plasma cells during this time periodcells during this time period

B cell/Helper T cell/Plasma cellB cell/Helper T cell/Plasma cell

2nd Immune Response2nd Immune Response

2nd immune response – when the body is 2nd immune response – when the body is exposed to previously encountered exposed to previously encountered antigensantigens

Response is faster and more prolongedResponse is faster and more prolonged

Antibodies more effective at binding to Antibodies more effective at binding to antigenantigen

2nd Immune Response (cont)2nd Immune Response (cont)

This is called This is called immunological memoryimmunological memory– Based on Based on memory cellsmemory cells produced during produced during

clonal selectionclonal selectionNot active during primary responseNot active during primary response

New clones of effector and memory cells New clones of effector and memory cells are the 2nd responseare the 2nd response

Section VSection V

Self/nonself Recognition with Self/nonself Recognition with Molecular MarkersMolecular Markers

Surface of LymphocytesSurface of Lymphocytes

Surfaces have antigen receptors that Surfaces have antigen receptors that detect foreign molecules that enter the detect foreign molecules that enter the bodybody– No lymphocytes reactive against the body’s No lymphocytes reactive against the body’s

own molecules under normal conditionsown molecules under normal conditions

Surface of Lymphocytes (cont.)Surface of Lymphocytes (cont.)

Self-toleranceSelf-tolerance – lack of a destructive – lack of a destructive immune response to the body’s won cellsimmune response to the body’s won cells– Develops (before birth) when T & B Develops (before birth) when T & B

lymphocytes begin to mature in the lymphocytes begin to mature in the thymus and bone marrowthymus and bone marrow

– Any lymphocytes with receptors for Any lymphocytes with receptors for molecules present in the body at that time molecules present in the body at that time are destroyedare destroyed

Only has antigen receptors for foreign Only has antigen receptors for foreign moleculesmolecules

Surface of Lymphocytes (cont.)Surface of Lymphocytes (cont.)

Mayor histocompatibility complex (MHC or HLA) Mayor histocompatibility complex (MHC or HLA) are glycoproteins within the plasma membrane; are glycoproteins within the plasma membrane; Histocompatibility MoleculesHistocompatibility Molecules– ““Self-markers” coded by a family of genesSelf-markers” coded by a family of genes– 20 MHC genes & 100 alleles for each gene20 MHC genes & 100 alleles for each gene– No one has the same markers except identical twinsNo one has the same markers except identical twins– Two main classes of MHC moleculesTwo main classes of MHC molecules

Class 1 MHC molecules on nucleated cells (fig. 43.16)Class 1 MHC molecules on nucleated cells (fig. 43.16)

Class 2 MHC molecules on specialized cells like (fig. 43.17) Class 2 MHC molecules on specialized cells like (fig. 43.17) macrophages, B, and active T cellsmacrophages, B, and active T cells

Section VISection VI

The Humoral Response; B The Humoral Response; B Cells Defend against Cells Defend against

Pathogens by Generating Pathogens by Generating Specific AntibodiesSpecific Antibodies

Background FactsBackground Facts

B cells differentiate into a clone of plasma B cells differentiate into a clone of plasma cells that secrete antibodies (fig. 43.17)cells that secrete antibodies (fig. 43.17)

Most effective against pathogen is blood Most effective against pathogen is blood or lymphor lymph

Memory cells produce and form the basis Memory cells produce and form the basis for 2nd immune responsefor 2nd immune response

Activation of B CellsActivation of B Cells

First step: binding of the antigen to specific First step: binding of the antigen to specific antigen-receptors on the surface of B cellsantigen-receptors on the surface of B cells

2nd step is the B cell activation involving 2nd step is the B cell activation involving macrophages & helper T cells; ends with macrophages & helper T cells; ends with the production of plasma cells (p. 909 fig the production of plasma cells (p. 909 fig 43.14 & p. 911, fig 43.17)43.14 & p. 911, fig 43.17)– MacrophageMacrophage phagocytes pathogens phagocytes pathogens

Activation of B cells (cont.)Activation of B cells (cont.)

– Pieces of digested antigen bind to class 2 Pieces of digested antigen bind to class 2 MHC molecules that are moved and present MHC molecules that are moved and present on the surface of macrophageon the surface of macrophage

– This is called an This is called an antigen-presenting cellantigen-presenting cell– Helper T cell specific of the presented antigen Helper T cell specific of the presented antigen

binds to self/nonself MHC complexbinds to self/nonself MHC complex– T cell is activated and forms a clone of helper T cell is activated and forms a clone of helper

T cellsT cells

Activation of B cells (cont.)Activation of B cells (cont.)

– These T cells secrete cytokines which elicit These T cells secrete cytokines which elicit other B cells with the same antigen other B cells with the same antigen (Fig. 43.17)(Fig. 43.17)

– T cell contact activates these B cells to form a T cell contact activates these B cells to form a clone of plasma cellsclone of plasma cells

– Each Each plasma cell (=effector cell)plasma cell (=effector cell) then then secretes antibodies specific for the antigensecretes antibodies specific for the antigen

Antibody and cell – mediated Antibody and cell – mediated ResponsesResponses

Activation of B cells (cont.)Activation of B cells (cont.)

– Each Each macrophagemacrophage can display a # of different can display a # of different antigens depending on the type of pathogen antigens depending on the type of pathogen phagocytizedphagocytized

– B cells again are specific and can bind to and B cells again are specific and can bind to and display only one type of antigendisplay only one type of antigen

– Macrophages are nonspecific & can enhance Macrophages are nonspecific & can enhance specific defense by selectively activating specific defense by selectively activating helper T cells which in turn activate B cells helper T cells which in turn activate B cells specific for the antigenspecific for the antigen

– Helper T cells are antigen-specificHelper T cells are antigen-specific

T-dependent & T-independent T-dependent & T-independent AntigensAntigens

T-dependent antigensT-dependent antigens – antigens that – antigens that evolve the cooperative response involving evolve the cooperative response involving macro’s, helper T’s, & B cellsmacro’s, helper T’s, & B cells

T-independent antigensT-independent antigens – antigens that – antigens that trigger humoral immune responses without trigger humoral immune responses without macrophage or T cell involvementmacrophage or T cell involvement– Stimulated by the antigen which binds to Stimulated by the antigen which binds to

several antigen receptors on the B cells several antigen receptors on the B cells surfacesurface

T-dependent & T-independent T-dependent & T-independent Antigens (cont.)Antigens (cont.)

– Usually weakerUsually weaker– No memory cells are generatedNo memory cells are generated

Whether dependent or independent, a B Whether dependent or independent, a B cell gives rise to a clone of plasma cellscell gives rise to a clone of plasma cells– Each Each effector celleffector cell secretes up to 2000 secretes up to 2000

antibodies / sec for 4 to 5 daysantibodies / sec for 4 to 5 days

Molecular Basis of Antigen-Molecular Basis of Antigen-Antibody SpecificityAntibody Specificity

Antigens are proteins or large Antigens are proteins or large polysaccharides of the outer part of polysaccharides of the outer part of pathogens or transplanted cellspathogens or transplanted cells– Can be coats of viruses, capsules, and cell Can be coats of viruses, capsules, and cell

walls of bacteriawalls of bacteria– Molecules of transplanted tissues and organ Molecules of transplanted tissues and organ

or blood cells are recognized as foreignor blood cells are recognized as foreign

Antibodies recognize the surface of an Antibodies recognize the surface of an antigen or the antigen or the epitopeepitope, not the entire , not the entire antigen molecule (see fig. fig 43.10), antigen molecule (see fig. fig 43.10), sometimes call the antigenic determinantsometimes call the antigenic determinant

Molecular Basis of Antigen-Molecular Basis of Antigen-Antibody Specificity (cont)Antibody Specificity (cont)

Antibodies are Proteins in a Class Called Antibodies are Proteins in a Class Called Immunoglobulins (lgs)Immunoglobulins (lgs)– See fig. 43.18See fig. 43.18– Structure associated with its functionStructure associated with its function– Y-shaped with 4 Y-shaped with 4 polypeptide chainspolypeptide chains: two : two

identical light chains and two identical heavy identical light chains and two identical heavy chainschains

– All 4 chains have constant C regions that vary All 4 chains have constant C regions that vary little in a.a. sequencelittle in a.a. sequence

Molecular Basis of Antigen-Molecular Basis of Antigen-Antibody Specificity (cont)Antibody Specificity (cont)

– At the tips of the Y are variable (V) regions; At the tips of the Y are variable (V) regions; show extensive variation from antibody to show extensive variation from antibody to antibodyantibody

Functions as antigen-binding sites that result in Functions as antigen-binding sites that result in specific shapes that fit and bind to specific antigen specific shapes that fit and bind to specific antigen epitopesepitopes

This site is responsible for the antibody’s ability to This site is responsible for the antibody’s ability to identify specific identify specific epitopeepitope and stem (constant) and stem (constant) regions through which the antibody inactivates or regions through which the antibody inactivates or destroys the antigenic invaderdestroys the antigenic invader

Molecular Basis of Antigen-Molecular Basis of Antigen-Antibody Specificity (cont)Antibody Specificity (cont)

– 5 types of 5 types of constant regionsconstant regions which are the five which are the five major classes of mammalian major classes of mammalian immunoglobinsimmunoglobins (table 43.18)(table 43.18)

IgMIgM – 5 Y-shapes monomers; appear in the initial – 5 Y-shapes monomers; appear in the initial exposure to an antigenexposure to an antigenIgGIgG – most abundant’ fights against bacteria, viruses, – most abundant’ fights against bacteria, viruses, and toxins in bloodand toxins in bloodIgAIgA – in mucous membranes; prevent bacteria and – in mucous membranes; prevent bacteria and viruses from attaching to epithelial surfaces; in saliva, viruses from attaching to epithelial surfaces; in saliva, tears, perspirationtears, perspirationIgDIgD – found on B cells; initiates differentiation of B cells – found on B cells; initiates differentiation of B cellsIgEIgE – stimulates basophils and mast cells to release – stimulates basophils and mast cells to release histamine and cause allergic reaction when triggered by histamine and cause allergic reaction when triggered by an antigenan antigen

Section VIISection VII

In the Cell-Mediated In the Cell-Mediated Response, T Cells defend Response, T Cells defend

Against Intracellular Against Intracellular PathogensPathogens

The Cell-Mediated Immune The Cell-Mediated Immune ResponseResponse

It is the defense that combats pathogens It is the defense that combats pathogens that have already entered cellsthat have already entered cells

Key components are helper T cells (TKey components are helper T cells (THH) ) and cytotoxic T cells (Tand cytotoxic T cells (TCC))

T cells cannot detect free antigens in the T cells cannot detect free antigens in the body fluidsbody fluidsThe receptor of a helper T cell recognizes The receptor of a helper T cell recognizes the molecular combination of an antigen the molecular combination of an antigen fragment with a class 2 MHCfragment with a class 2 MHC

The Cell-Mediated Immune The Cell-Mediated Immune Response (cont.)Response (cont.)

The receptor of a cytotoxic T cell The receptor of a cytotoxic T cell recognizes the combination of an antigen recognizes the combination of an antigen fragment with a class 1 MHC moleculefragment with a class 1 MHC molecule

The MHC-antigen complex displayed on The MHC-antigen complex displayed on an infected body cell stimulates T cells to an infected body cell stimulates T cells to multiply and form clones of Tmultiply and form clones of TH H and Tand TCC

which recognized the pathogen which recognized the pathogen

The Cell-Mediated Immune The Cell-Mediated Immune Response (cont.)Response (cont.)

(T(THH) cells stimulate B cells to secrete antibodies ) cells stimulate B cells to secrete antibodies

against T-dependent antigens in a humoral against T-dependent antigens in a humoral responseresponse

(T(THH) cells also activate other types of T cells to ) cells also activate other types of T cells to

mount cell-mediated responses to antigensmount cell-mediated responses to antigens

Helper T cells are able to stimulate other Helper T cells are able to stimulate other lymphocytes by receiving and sending cytokines lymphocytes by receiving and sending cytokines such as interleuking-2. Increased levels of such as interleuking-2. Increased levels of cytokines also increase the cell-mediated cytokines also increase the cell-mediated response by stimulating another class of T-cells response by stimulating another class of T-cells into cytotoxic cells (effector cells)into cytotoxic cells (effector cells)

Section VIIISection VIII

Complement Proteins Complement Proteins Participate in Both Nonspecific Participate in Both Nonspecific

and Specific Defensesand Specific Defenses

Complement Proteins circulate in Complement Proteins circulate in the Blood in Inactive Formsthe Blood in Inactive Forms

Complement protein attaches to, and Complement protein attaches to, and bridges the gap between, two adjacent bridges the gap between, two adjacent antibody moleculesantibody molecules

This antibody-complement activates This antibody-complement activates proteins to from a membrane attack proteins to from a membrane attack complexcomplex

Complement Proteins circulate in Complement Proteins circulate in the Blood in Inactive Forms (cont.)the Blood in Inactive Forms (cont.)This membrane attack complex lyses the This membrane attack complex lyses the pathogen’s membrane producing a lesion and pathogen’s membrane producing a lesion and the lyses of the cellthe lyses of the cellThere is also a nonspecific defense mechanismThere is also a nonspecific defense mechanismComplement and phagocytes work together two Complement and phagocytes work together two waysways– Opsonization where the proteins attach to a foreign Opsonization where the proteins attach to a foreign

cell and stimulate phagocytes to engulf the cellcell and stimulate phagocytes to engulf the cell– In immune adherence, where they coast a microbe In immune adherence, where they coast a microbe

which causes to adhere to blood vessel walls and which causes to adhere to blood vessel walls and sets it up for circulating phagocytessets it up for circulating phagocytes