The body’s defenders

Core concepts Infectious diseases are caused by pathogens Nonspecific defenses against infection

Plants and animals have mechanisms that are not targeted to specific pathogens that help them combat infection

Skin and mucous membranes provide first-line barriers to infection Phagocytic cells, inflammation, and antimicrobial proteins function as the second line of defense

Specific immunity arises from lymphocyte-antigen interactions Lymphocytes provide the specificity and diversity of the immune system Antigens interact with specific lymphocytes, inducing immune responses and immunological

memory Lymphocyte development gives rise to an immune system that distinguishes self from nonself

Immune responses take two forms: humoral and cell-mediated Helper T-lymphocytes function in both humoral and cell-mediated immunity Cytotoxic T-cells counter intracellular pathogens B-cells make antibodies against extracellular pathogens Memory B- and T-cells are responsible for faster and stronger secondary immune responses

Immunity in health and disease Immunity can be achieved naturally or artificially The immune system limits blood transfusion and tissue transplantation Abnormal immune function can lead to disease AIDS is an immunodeficiency disease caused by a virus

Keywords ABO blood groups active immunity agglutination AIDS allergy anaphylactic shock antibody antigen antigen receptor antigen-presenting cell apoptosis autoimmune disease B cell basophils CD4 CD8 cell-mediated immunity

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Pathogens and disease

Fungi

Viruses

Protozoa

Bacteria Large parasites

Two major types of defenses

INNATE (NONSPECIFIC)IMMUNITY

Rapid responses to a broad range of microbes

ACQUIRED (SPECIFIC) IMMUNITY

Slower responses to

specific microbesExternal defenses Internal defenses

Skin

Mucous membranes

Secretions

Phagocytic cells

Antimicrobial proteins

Inflammatory response

Natural killer cells

Humoral response(antibodies)Cell-mediated response(cytotoxic lymphocytes)

Invadingmicrobes

(pathogens)

Innate (nonspecific) immunity First line: External defenses

External defenses

Microbes

MACROPHAGE

Vacuole Lysosomecontainingenzymes

Phagocytic cellInnate immunity Second line: Internal defenses Phagocytes

Attach to and ingest invading microorganisms

Initiates the inflammatory response○ Macrophages – migrants or in

lymph organs

Antimicrobial proteins Complement system – lysis of

invading cells, triggers inflammation Interferons – activate macrophages,

prevent cell-to-cell spread Defensins – secreted by macrophages

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Inflammatory response

Innate immunity Second line: Internal defenses (con’t.)

http://www.sumanasinc.com/webcontent/anisamples/dynamicillustrations/inflammatory.html

Chemicals involved• Histamines• Prostaglandins• Chemokines• Pyrogens

Innate immunity Second line: Internal defenses (con’t.)

Natural killer (NK) cellsAttack virus-infected

body cells and cancer cells

Apoptosis (cell death) in cells attacked

Coelomocytes and hemocytes – phagocytes in invertebrates

Specific (acquired) immunityThird line of defenseLymphocytes

In blood and lymph Types

1. B – cells – mature in marrow

2. T – cells – mature in thymus○ Helper○ Cytotoxic/Killer○ Suppressor○ Memory

Activated by cytokines from phagocytes

Display specificity to epitopes on antigens (antibody generator)

Have specific membrane-bound antigen-receptors

Two types of specific immune responses

B and T cells generate clones of1)short-lived activated effector cells2)long-lived memory cells

MHC molecules and T cell function

Class I MHC moleculesMost nucleated cells of the bodyInfected/cancerous cells display parts of

foreign antigens on surfacesRecognized by cytotoxic T cells

Class II MHC moleculesDendritic cells, macrophages, B cells

(APCs) display phagocytized antigen fragments on surfaces

Recognized by helper T cells T cells that have receptors for self-

molecules are destroyed self-tolerance

Antibody action

Immunity – memory cells initiate a faster, more efficient response upon reinfection

Active immunity Own system

develops antibodies Develops naturally in

response to infection Develops following

immunization Long-lasting

protection but may take a long time

Passive immunity Antibodies are passed

from mother to fetus via the placenta

Antibodies are passed from mother to infant via breast milk (colostrum)

Antibodies may be injected into a nonimmune person

Immediate, short-term protection

Blood groups and transfusions Problems with transfusions and transplants Antigens on RBC’s will determine a person’s

blood type: A, B, AB, O blood Another RBC antigen: Rh factor Rh+ or

Rh-

Immune disorders/diseases Allergies –

hypersensitive responses to antigens called allergens

Autoimmune diseases – immune system loses tolerance for self and turns against certain molecules of the body

Immunodeficient diseases Inborn or primary Acquired or secondary

○ AIDS – HIV attacks CD4 molecules on helper T cells

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