Chapter 43-Recognition and ResponsePathogens: agents that cause disease infect a wide range of animals, including humansImmune system: recognizes foreign bodies and responds with the production of immune cells and proteinsDefends the body against viruses, bacteria, protozoans, worms and toxic molecules2 types of defense-Innate Immunity: defense active immediately upon infectionVertebrates also have adaptive immunityInnate immunity: present before any exposure to pathogens and iseffective from the time of birthnonspecific responses to pathogensConsist of1) External Barriers (Skin, Mucus, Earwax)2) Internal Cellular defenses (White blood cells)3) Chemical Defenses (Inflammatory response)Adaptive Immunity or Acquired Immunity: develops after exposure to agents such as microbes, toxins or other foreign substances.Specific responses to pathogensAntibodies, cytotoxins, lymphocytes-Concept 43.1: Innate immunity, recognition and response rely on traits common to groups of pathogens-Innate Immunity of VertebratesImmune system of mammals is the best understood of the vertebratesIncluded barrier defenses, phagocytosis, antimicrobial peptidesAdditional defenses are unique to vertebrates; Natural Killer (NK) cells, interferons, and the inflammatory response-Barrier DefensesInclude skin and causes membranes of tractsMucus traps and allows for the removal of microbesSaliva, mucus, and tears are hostile to microbesLow pH of skin and digestive system prevents growth of bacteria-Cellular Innate DefensesPathogens entering the mammalian body are subject to phagocytosisSome white blood cells (Neutrophil and monocytes) can engulf pathogens in the bodyPhagocytic cells recognize groups of pathogens by the TLRs, toll-like receptorswhite blood cell engulf a microbe, then fuses with a lysosome to destroy the microbeDifferent type of phagocytic cells1) Neutrophils: engulf and destroy pathogens2) Macrophages: found through out the body3) Dendritic cells: stimulate development of adaptive immunity4) Eosinophils: discharge destructive EnzymesNatural Killer cells circulate though the body and detect abnormal cellsRelease chemicals leading to the cell death, inhibiting the spread of virally infected or cancerous cellsMany cellular innate defenses involve the lymphatic system-Antimicrobial peptides and proteinsPeptides and proteins function in innate defense by attacking pathogens orimpeding their reproductionInterferon proteins provide innate defense, interfering with viruses and helping activate macrophages30 proteins make up the complement system, which causes lysis of invading cells and trigger inflammation-Inflammatory ResponsesInflammatory Responses: such as pain and swelling is brought about by molecules released upon injury or infectionMast Cells: type of cell found in connective tissue, release histamine, which triggers blood vessels to dilate and become more permeable, leads to rednessand swellingActivated macrophages and neutrophils release cytokines, signaling molecules that exchange the immune response.These changes increase local blood supply and allow more phagocytes and antimicrobial proteins to enter tissueInflammation can be either local or systemic (through out body)Fever is a systemic inflammatory response triggered by pyrogensSeptic Shock is a life-threating condition caused by an overwhelming inflammatory responsehigh fever, low blood flow, low blood pressureVery old, very young peopleFatal 1/3 of the time-Natural Killer CellsAll cells in body (Except RB cells) have a class 1 MHC protein on their cell structure, NK cell ignores these cells-Evasion of Innate Immunity by pathogensSome pathogens alter structure to prevent recognition and break down, TB(tuberculosis does this)-Concept 43.2: In adaptive immunity, receptors provide pathogen specific recognitionThe adaptive response relies on two types of lymphocytes or white blood cellsLymphocytes contribute to Immunological memory, an enhanced response to foreign molecule that had been encountered previouslyLymphocytes that mature in the thymus above the heart are called T-Cells, and those that mature in bone marrow are called B-Cells.antigens: substances that can elicit a response from a B or T cell Exposure to the pathogen activates B and T cells with antigen receptors specific for parts of that pathogenSingle B or t cell has above 100,000 identical antigen receptorsEpitope: small accessible part of an antigen that binds to an antigen receptorB and T cells have a receptor protein that can bind to foreign moleculesEach individual lymphocyte is specialized to recognize a specific type of molecule-Antigen Recognition by B cells and AntibodiesEach B-cell antigen receptor has y-shaped molecule with 2 identical heavy chains, and 2 identical light chainsThe constant regions of the chains vary little among B cells, where as the variable regions differ greatlyThis gives rise to cells that secrete a soluble form of the protein called antibody or immunoglobin (Ig)Secreted anti-bodies are similar to B cell receptors but lack trans membrane regions that anchor receptors in the plasma membraneMillions of different types of B-Lymphocytes exist, each type secretes a specific antibody-Antigen Recognition by T-CellsEach T-Cell receptor consist of 2 different polypeptide chains (called alpha and beta)The tips of the chains form a variable (V) region, the rest is a constant © region.T-Cell and B cell antigen receptors are functionally differentT-Cells bind to antigen fragments displayed or presented on host cellThese antigen fragments are bound to cell-surface proteins called MHC moleculesMHC( major histocompatibility Complex) molecules are host proteins that display the anti-gen fragments on the cells surfaceInfected cells, MHC molecules bind and transport antigen fragments to cell surface a process called antigen presentationA T-Cell can then bind both the antigen fragment and the MHC moleculeThis interaction is necessary for the T-Cell to participate in the adaptive immune response-B-Cell and T-Cell DevelopmentThe adaptive immune system has four major characteristicsdiversity of lymphocytes and receptorsSelf-tolerance: lack of reactivity against an animals own moleculesSome B and T-cells with receptors for the body’s own molecule are destroyed by
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