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

• chemokines• class I MHC• class II MHC• clonal selection• complement fixation• complement system• cytokine• cytotoxic T cell• effector cell• eosinophils• helper T cell• histamine• HIV• humoral immunity• immunity• immunodeficiency disease• immunoglobulin• inflammatory response• interferon• interleukin• lysozyme• macrophages• major histocompatibility

complex• mast cells• membrane attack complex

• memory cell• monocytes• natural killer cells• neutrophils• nonspecific defense• opportunistic disease• passive immunity pathogen• perforin• phagocytosis• plasma cell• primary immune response• prostaglandins• pyrogens• Rh factor• secondary immune

response• suppressor T cell• T cell• T cell receptor• target cell• tumor antigen• vaccine

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

SkinMucous 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

Tears

Mucus, cilia

Skin, oil,

sweat, acidity

Mouth bacteria,

saliva

Gastric juice

Intestinal flora

Acid conditions

Microbes

MACROPHAGE

Vacuole Lysosomecontainingenzymes

Phagocytic cellInnate immunity Second line: Internal defenses

Phagocytes Attach to and ingest invading

microorganisms Initiate the inflammatory

response Macrophages – migrants or in lymph

organs, lungs, kidneys, connective tissues Antimicrobial proteins

Complement system – lysis of invading cells, triggers inflammation

Interferons – activate macrophages, prevent cell-to-cell spread of viruses

Defensins – secreted by macrophages to damage pathogens

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70%chemotaxis

5% 1.5% histamine

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

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Chemicals involved• Histamines• Prostaglandins• Chemokines• Pyrogens

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

Natural killer (NK) cells Attack virus-infected body

cells and cancer cells Apoptosis (cell death) in

cells attacked Coelomocytes and

hemocytes – phagocytes in invertebrates

Specific (acquired) immunityThird line of defense

Lymphocytes In blood and lymph Types

1. B – cells – mature in marrow2. T – cells – mature in thymus

Helper Cytotoxic/Killer Regulatory/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 cells

2) long-lived memory cells

MHC molecules and T cell function Class I MHC molecules

Most nucleated cells of the body Infected/cancerous cells display parts

of foreign antigens on surfaces Recognized by cytotoxic T cells

Class II MHC molecules Dendritic 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

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Clonal selectionantigen-driven cloning of

lymphocytes

Antigen binds to receptor on lymphocyte

Lymphocyte is activated

Thousands of clones specific for the antigen are produced

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 (artificial immunity)

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 (artificial immunity)

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 (SLE, diabetes type I, rheumatoid arthritis)

Immunodeficient diseases Inborn or primary (severe

combined ID) Acquired or secondary

AIDS – HIV attacks CD4 molecules on helper T cells, macrophages, dendritic cells

IgE antibodies bind to receptors or mast cells.

1On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recog-nize and bind the allergen.

2Degranulation of the cell,triggered by cross-linking of adjacent IgE molecules, releases histamine and other chemicals, leading to allergysymptoms.

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Allergen

IgE

Histamine

GranuleMast cell