43 The Immune System Animal body ideal habitat for pathogens o Nutrients protection and transport Immune system defenses that enable an animal to avoid treat infection Innate immunity defense active immediately upon infection and is same whether or not the pathogen has already been encountered o Outer covering skin shell that provides barriers to entry Some open surfaces needed for exchange absorption so they use chemicals or secretions trap kill pathogens Molecular recognition receptor molecules bind specifically to molecules from foreign cells viruses o Receptor proteins bind to molecules structures absent in animals but common to viruses bacteria or microbes Activates other defenses for immunity Adaptive immunity vast arsenal of receptors that recognize a part of a specific Acquired immune response activated after innate immune response pathogen o Only invertebrates o Slower o Enhanced by previous exposure o Humoral response Antibodies in fluid o Cell mediated response Cytotoxic cells defend against infection in body cells Innate immunity recognition and response rely on common traits among pathogens Innate immunity in invertebrates o 1st line Insects use exoskeleton Chitin barrier to outside Chitin in intestine blocks infection in pathogens in food Lysozyme enzyme that breaks down bacterial cell walls Hemocytes cells that travel in hemolymph Some phagocytize bacteria and foreign substances Others trigger production of chemicals that kill pathogens and trap large parasites Hemocytes and other cells also make antimicrobial peptides short chains of amino acids that circulate and kill inactivate fungi and bacteria by disrupting plasma membranes o Immune cells of insects bind to molecules only in outer layers of fungi bacteria Innate responses specific to groups of pathogens and cause production of specific antimicrobial restraints To study this they knock out specific genes and then infect the fly to see which polypeptides on for what Innate immunity of vertebrates o Barrier defenses Epithelium blocks entrance of many pathogens Skin mucous membranes lining digestive respiratory and reproductive tracts o Mucous viscous fluid that traps invader Body secretions make environment hostile to invade o Lysozyme in tears saliva and mucous secretions break down bacterial cell walls o Secretions from oil sweat glands give skin a pH of 3 5 Cellular innate defenses o Phagocytosis Detect fungal bacterial components using receptors Toll like Receptor TLR binds to fragments of molecules characteristic of a set of pathogens Phagocytic cells eat and trap pathogens in a vacuole which then fuses with a lysosome Gases in lysosome poison the pathogen Lysozyme and other enzymes degrade pathogen component 2 main phagocytic cells o Neutrophils circulate in the blood and are attracted by signals from infected cells and then engulf destroy pathogens o Macrophages larger phagocytic cells Some migrate and some stay in organs tissues that are likely to come in contact with pathogens 2 other types of phagocytic cells provide additional innate immunity o Dendritic cells stimulate adaptive immunity against defense function pathogens they encounter and engulf Mainly populate tissues that contact the environment o Esinophils low phagocytic activity but play a role in defending against multicellular invaders parasitic worms Discharge destructive enzymes Found beneath mucosal surfaces o Natural killer cells circulate and detect abnormal surface proteins of virus infected and cancerous cells Release chemicals that lead to cell death Many cellular innate defenses involve the lymphatic system Macrophages found in lymph nodes where they engulf pathogens from interstitial fluid o Dendritic cells lie outside the lymphatic system but migrate to lymph nodes after encountering pathogens and interact with other cells to stimulate adaptive immunity o Antimicrobial peptides and proteins Pathogen recognition stimulates the release of peptides proteins that attract impede reproduction of pathogens Some like those of invertebrates damage broad groups of pathogens Interferons proteins that provide innate defense by interfering with viral infections Limiting cell to cell spread of viruses o Virus infected cells secrete these to stimulate nearby uninfected cells to secrete substances to inhibit viral reproduction Some white blood cells secrete an interferons that activates macrophages Complement system 30 proteins in blood plasma that are activated by surface molecules on microbes Lead to lysis of invading cells Also functions in inflammatory response o Inflammatory response changes brought about by signaling molecules released upon injury infection Histamine stored in granules vesicles of mast cells in connective tissues Histamines Released at sites of injury Dilates capillaries and makes them more permeable Cytokines molecules released by activated macrophages and neutrophils that enhance immune response Promote blood flow redness and increased temperature Accumulation of pus fluid rich in white blood cells dead pathogens and cell debris Severe damage or infection could lead to a systemic response Fever activated macrophages release substances that turns up body thermostat Might increase phagocytosis and accelerate tissue repair Septic shock overwhelming systemic response High fever Low blood pressure Poor blood flow in the capillaries Evasion of innate immunity by pathogens o Capsule interferes with molecular recognition and phagocytosis o Resist breakdown in lysosome In Adaptive Immunity Receptors Provide Pathogen Specific Recognition Lymphocytes T and B cells from stem cells in bone marrow o T cells lymphocytes that migrate from the marrow to the thymus where they develop into T cells o B cells lymphocytes that stay and mature in the marrow o 3rd type stays in the blood and develops into natural killer cells of innate immunity Antigen any substance that causes a response from a B or T cell usually polysaccharides or proteins on cell surface o Toxins secreted by bacteria o Antigen receptor protein that binds to antigens specific to 1 molecule from 1 pathogen o Epitope small portion of the antigen that binds to the antigen receptor o B T cells are specific to each specific epitope Antigen recognition by B cells and Antibodies o Bind to antigens in body fluids o Each B cell antigen receptor is a Y shaped molecule with 4 polypeptide chains linked by disulfide bridges 2 identical heavy chains 2 identical light chains Anchored by
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