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The body’s defenders

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

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The body’s defenders

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  1. The body’s defenders

  2. 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

  3. Keywords • 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 • 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 • 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

  4. Pathogens and disease Fungi Viruses Protozoa Bacteria Large parasites

  5. INNATE (NONSPECIFIC) IMMUNITY Rapid responses to a broad range of microbes ACQUIRED (SPECIFIC) IMMUNITY Slower responses to specific microbes External defenses Internal defenses Skin Phagocytic cells Humoral response (antibodies) Mucous membranes Antimicrobial proteins Secretions Inflammatory response Cell-mediated response (cytotoxic lymphocytes) Invading microbes (pathogens) Natural killer cells Two major types of defenses

  6. Innate (nonspecific) immunity First line: External defenses Mucus, cilia Tears Mouth bacteria, saliva Skin, oil, sweat, acidity Intestinal flora Gastric juice Acid conditions

  7. Microbes MACROPHAGE Vacuole Lysosome containing enzymes Innate immunity Second line: Internal defenses Phagocytic cell 1 • 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 2 3 4 5 6

  8. 70% chemotaxis 5% 1.5% histamine

  9. Innate immunity Second line: Internal defenses (con’t.) • Inflammatory response • Chemicals involved • Histamines • Prostaglandins • Chemokines • Pyrogens http://www.sumanasinc.com/webcontent/anisamples/dynamicillustrations/inflammatory.html

  10. 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

  11. Specific (acquired) immunityThird line of defense Lymphocytes • In blood and lymph • Types • B – cells – mature in marrow • 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

  12. Two types of specific immune responses • B and T cells generate clones of • short-lived activated effector cells • long-lived memory cells

  13. 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

  14. image/svg+xml \\ Clonal selectionantigen-driven cloning of lymphocytes

  15. Antibody action

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

  17. 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

  18. 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-

  19. 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

  20. IgE Allergen Histamine 1 3 2 Granule Mast cell 2 Degranulation of the cell, triggered by cross-linking of adjacent IgE molecules, releases histamine and other chemicals, leading to allergy symptoms. 3 1 IgE antibodies bind to receptors or mast cells. On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recog- nize and bind the allergen.

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