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| 16.1 The Importance of Cell Surfaces 1. Foreign antigens (molecules) elicit an immune response from a host. 2. Antibodies and cytokines produced by the immune system attack foreign antigens. 3. As many as 20,000 genes in the human genome may be, directly or indirectly, involved in an immune response. Blood Groups 1. Results of early transfusions were inconsistent. 2. With the discovery of human blood groups systems, properly matched donor and recipient types resulted in successful transfusions. 3. Blood types, including the ABO groups, Rh factor, and others, result from self antigen patterns on red blood cells. 4. Rh incompatibility may put a fetus at risk. 5. RhoGAM can be used to prevent Rh incompatibility. The Human Leukocyte Antigens 1. In addition to blood group antigens, a large number of cell surface molecules are recognized by the immune system. 2. Many of the cell surface proteins that help to establish immunity are encoded by the approximately seventy genes of the major histocompatibility complex (MHC) located on chromosome 6 in humans. 3. Class I and II genes of the MHC encode human leukocyte antigens (HLA). 4. Class III genes produce plasma proteins involved in the immune response. 5. HLA antigens on leukocytes are involved in processing of foreign antigens. 6. HLA proteins are each encoded by several genes with many alleles and as a result only 2 in every 20,000 unrelated people match for the six major HLA genes by chance. 7. Individuals with certain HLA combinations have an increased risk of developing certain HLA-linked diseases. 16.2 The Immune System 1. At the cellular level the immune system consists of various types of lymphocytes and macrophages. 2. The immune response consists of an immediate, generalized, innate immunity and a slower, more specific adaptive immunity. Physical Barriers and the Innate Immune Response 1. Skin, mucous membranes, tears, and saliva are examples of physical and chemical barriers that keep pathogens from entering the body. 2. Pathogens that breach this barrier encounter an innate immune response consisting of inflammation, phagocytosis, complement, collectins, and cytokines. The Adaptive (Acquired) Immune Response 1. The innate response is rapid (minutes) while the aquired immune response must be stimulated to action and takes days to respond. 2. The acquired immune response is divided into the humoral and cellular immune responses. Both of these responses differ from the innate immune response in that they are more complex, highly specific and each has a cellular component with memory. 3. The humoral response involves B cells that secrete antibodies in order to neutralize, clump, and stimulate the destruction of pathogens by recognizing and binding specific foreign antigens. 4. Antibodies are made of Y-shaped polypeptides consisting of constant and variable regions. 5. The astounding diversity of antibody binding activities is due to a shuffling of gene pieces (exons) encoding antibody polypeptide products in B cells. 6. In the cellular immune response, helper T cells stimulate B cells to manufacture antibodies and cytotoxic T cells to secrete cytokines. 7. Some T cells bind to nonself cells and virus-covered cells and burst them. Other T cells function to coordinate the immune response. 16.3 Abnormal ImmunityInherited Immune Deficiencies 1. Inherited immune deficiencies represent defects in the genes that encode proteins involved in immunity. Acquired Immune Deficiency Syndrome 1. Acquired immune deficiency syndrome is caused by HIV. 2. HIV replicates very rapidly, and T cell production matches it until the immune system is overwhelmed and AIDS begins. 3. HIV is a retrovirus that injects its RNA into host cells by binding receptors. 4. Reverse transcriptase then copies viral RNA into DNA. 5. HIV uses the cell’s protein synthesis machinery to mass produce itself; then the cell bursts, releasing virus. 6. Reverse transcriptase and protease inhibitors have been effective in slowing down HIV. 7. A new fusion inhibitor was introduced in 2002. 8. HIV continually mutates, and may become resistant to drugs. Autoimmunity 1. In autoimmune disorders, autoantibodies attack healthy tissue. 2. These conditions may be caused by a virus that borrows a self antigen, Tcells that never learn to recognize self, or healthy cells bearing antigens that resemble nonself antigens. 3. Some conditions thought to be autoimmune may actually reflect an immune system response to retained fetal cells. 4. Mutations in some genes may present the symptoms of an autoimmune disease. Allergies 1. An overly sensitive immune system causes allergies. 2. In an allergic reaction, allergens bind to IgE antibodies on mast cells, which release allergy mediators. 3. A subset of helper T cells secrete cytokines that contribute to allergy symptoms. 16.4 Altering Immune FunctionVaccines 1. Vaccines are disabled pathogens or their parts that elicit an immune response, protecting against infection by the active pathogen. Immunotherapy 1. Immunotherapy uses immune system components to fight disease. 2. Hybridomas are artificial cells that consist of a B cell fused with a cancer cell and produce monoclonal antibodies (Mabs) that can target specific antigens. 3. Cytokines boost immune function and destroy cancer cells. Transplantation 1. Autografts transfer tissue from one part of a person's body to another. 2. Isografts are tissue transfers between identical twins. 3. Allografts involve tissue transfers between members of the same species. These transplants can cause tissue rejection reactions. 4. A Xenograft is a cross species transplant. A danger of these transplants is that they can set off a hyperacute rejection. 5. Graft-versus-host disease involves a rejection of recipient tissues by transplanted bone marrow. 6. The success rate of transplants is improved by the use of immunosuppressive drugs, by stripping antigens from donor tissue, and by matching donor to the recipient. 16.5 A Genomic View of Immunity-The Pathogen's Perspective 1. Analyzing the genomes of pathogens may reveal the molecular basis of pathogenesis. Crowd Diseases 1. Crowd diseases readily spread through populations and can cause epidemics. 2. Native populations with no immunity can be devastated by introduction of new diseases. Bioweapons 1. A variety of pathogens have been adapted to military use including anthrax. |