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 memory cell chemokines monocytes 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 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

Pathogens and disease Fungi Viruses Protozoa Large parasites Bacteria

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

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

Innate immunity Second line: Internal defenses Microbes MACROPHAGE Vacuole Lysosome containing enzymes Phagocytic cell Innate immunity Second line: Internal defenses 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

70% chemotaxis 5% 1.5% histamine

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

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) immunity Third 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

Two types of specific immune responses B and T cells generate clones of short-lived activated effector cells 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

Clonal selection antigen-driven cloning of lymphocytes image/svg+xml \\ Clonal selection antigen-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 Passive 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. 1 On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recog- nize and bind the allergen. 2 Degranulation of the cell, triggered by cross-linking of adjacent IgE molecules, releases histamine and other chemicals, leading to allergy symptoms. 3 Allergen IgE Histamine Granule Mast cell