Chapter 43 Recognition and Response including humans toxic molecules 2 types of defense Pathogens agents that cause disease infect a wide range of animals Immune system recognizes foreign bodies and responds with the production of immune cells and proteins Defends the body against viruses bacteria protozoans worms and Innate Immunity defense active immediately upon infection Vertebrates also have adaptive immunity Innate immunity present before any exposure to pathogens and is effective from the time of birth nonspecific responses to pathogens Consist of 1 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 pathogens Antibodies cytotoxins lymphocytes Concept 43 1 Innate immunity recognition and response rely on traits common to groups of pathogens Innate Immunity of Vertebrates Immune system of mammals is the best understood of the vertebrates Included barrier defenses phagocytosis antimicrobial peptides Additional defenses are unique to vertebrates Natural Killer NK cells interferons and the inflammatory response Barrier Defenses Include skin and causes membranes of tracts Mucus traps and allows for the removal of microbes Saliva mucus and tears are hostile to microbes Low pH of skin and digestive system prevents growth of bacteria Cellular Innate Defenses Pathogens entering the mammalian body are subject to phagocytosis Some white blood cells Neutrophil and monocytes can engulf pathogens in the body like receptors Phagocytic cells recognize groups of pathogens by the TLRs toll white blood cell engulf a microbe then fuses with a lysosome to destroy the microbe Different type of phagocytic cells 1 Neutrophils engulf and destroy pathogens 2 Macrophages found through out the body 3 Dendritic cells stimulate development of adaptive immunity 4 Eosinophils discharge destructive Enzymes Natural Killer cells circulate though the body and detect abnormal cells Release chemicals leading to the cell death inhibiting the spread of virally infected or cancerous cells Many cellular innate defenses involve the lymphatic system Antimicrobial peptides and proteins Peptides and proteins function in innate defense by attacking pathogens or impeding their reproduction helping activate macrophages Interferon proteins provide innate defense interfering with viruses and 30 proteins make up the complement system which causes lysis of invading cells and trigger inflammation Inflammatory Responses Inflammatory Responses such as pain and swelling is brought about by molecules released upon injury or infection Mast Cells type of cell found in connective tissue release histamine which triggers blood vessels to dilate and become more permeable leads to redness and swelling Activated 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 tissue Inflammation can be either local or systemic through out body Fever is a systemic inflammatory response triggered by pyrogens Septic Shock is a life threating condition caused by an overwhelming inflammatory response high fever low blood flow low blood pressure Very old very young people Fatal 1 3 of the time Natural Killer Cells structure NK cell ignores these cells All cells in body Except RB cells have a class 1 MHC protein on their cell Evasion of Innate Immunity by pathogens Some pathogens alter structure to prevent recognition and break down TB tuberculosis does this Concept 43 2 In adaptive immunity receptors provide pathogen specific recognition The adaptive response relies on two types of lymphocytes or white blood cells Lymphocytes contribute to Immunological memory an enhanced response to foreign molecule that had been encountered previously Lymphocytes 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 pathogen Single B or t cell has above 100 000 identical antigen receptors Epitope small accessible part of an antigen that binds to an antigen B and T cells have a receptor protein that can bind to foreign molecules Each individual lymphocyte is specialized to recognize a specific type of receptor molecule Antigen Recognition by B cells and Antibodies Each B cell antigen receptor has y shaped molecule with 2 identical heavy chains and 2 identical light chains variable regions differ greatly antibody or immunoglobin Ig The constant regions of the chains vary little among B cells where as the This gives rise to cells that secrete a soluble form of the protein called Secreted anti bodies are similar to B cell receptors but lack trans membrane regions that anchor receptors in the plasma membrane Millions of different types of B Lymphocytes exist each type secretes a specific antibody Antigen Recognition by T Cells Each T Cell receptor consist of 2 different polypeptide chains called alpha The tips of the chains form a variable V region the rest is a constant T Cell and B cell antigen receptors are functionally different T Cells bind to antigen fragments displayed or presented on host cell These antigen fragments are bound to cell surface proteins called MHC and beta region molecules MHC major histocompatibility Complex molecules are host proteins that display the anti gen fragments on the cells surface Infected cells MHC molecules bind and transport antigen fragments to cell surface a process called antigen presentation A T Cell can then bind both the antigen fragment and the MHC molecule This interaction is necessary for the T Cell to participate in the adaptive immune response B Cell and T Cell Development The adaptive immune system has four major characteristics diversity of lymphocytes and receptors Self tolerance lack of reactivity against an animals own molecules Some B and T cells with receptors for the body s own molecule are destroyed by APOPTOSIS programmed cell death B and T cells proliferate after activation In the lymph node a antigen is exposed to a steady stream of lymphocytes until a match is made Immunological Memory Immunological Memory infection or
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