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Immune System Part IV: The Adaptive Immune System and Humoral Immunity Adaptive Immune System (Specific Immune System): Humoral Immunity Humoral Immunity • Selected B cells produce copious amounts of antibodies that interact with antigens found on pathogens. • Needs the support of helper T cells. Adaptive Immune System: Humoral Immunity • An antigen is any material that stimulates selected B cells to produce copious amounts of antibodies. • An epitope is the part of an antigen to which the antibody attaches. An antigen can have more than one epitope or type of epitope. • Antigens include bacterial cell walls, viral parts, flagella, etc. Adaptive Immune System: Different Epitopes on Different Antigens Different epitopes found on different types of antigens. Humoral Immunity: Selecting B cells • Naïve B cell receptors are different for each B cell. • Antigens attach to a receptor site on the B cell. • Antigens are brought into the cytoplasm of the B cell. • Antigens attach to MHC II proteins and are transported to the cell membrane. 5 Humoral Immunity: Cloning Selected B cells • An activated helper T cell makes a match with MHC II/AG complex. • Helper T cell secretes cytokines which causes the B cell to reproduce and making plasma B cells and memory B cells. Humoral Immunity: Cloning Selected B cells • For this particular selected B cell, thousands of B plasma cells are cloned. They are identical to the original B cell. • Each plasma B cell can synthesize 2,000 identical AB per second. This illustrates how out of thousands of different naïve B cells, only the one with the correct receptor site is selected and cloned. Antibodies Can Inactivate Antigens 9 Opsonization and Inactivating an Antigen Opsonization: Certain bacterial cells have so many AG determinants that the antibodies coat the bacteria cell. The constant regions stick out (called the FC region). The phagocytes have FC receptors. This interaction allows the phagocyte to roll over the pathogen and phagocytosis occurs. 10 Activation of B-Cells Another drawing of B cell selection and activation of plasma cells. 11 Homeostasis: Halting the Attack • Regulatory T cells (Treg) help to halt the immune response. • Do not know how they are activated; possibly through antigens. • Thought to stop any further naïve B or T cells from being activated. The immune response then stops because activated immune cells die due to their short life span. 13 Secondary Immune Response • Memory B cells and T cells are selected for when exposure to a subsequent pathogen occurs and the memory cells are a match for the antigen. • Memory B cells and T cells quickly reproduce, making plasma B cells, helper T cells and cytotoxic T cells (effector cells). • Plasma B cells begin to make AB and cytotoxic T cells begin to destroy infected cells. Secondary Immune Response Preventing Disease with Vaccines Immunity-Subsequent exposures to pathogens do not result in the disease. Active immunity causes memory B and T cells to be made. Passive immunity results from obtaining pre-made antibodies with no memory cells being made. 16 Type of Immunity Natural active immunity- (ex. mumps) organism is exposed to the actual pathogen and gets the disease. Memory cells are made. Subsequent exposure to the pathogen does not cause the disease. Artificial active immunity- (vaccine) person is given inactive parts of the pathogen so that memory cells are made. Exposure to the pathogen does not cause the disease. Natural passive immunity- AB in breast milk and the antibodies of a pregnant woman cross the placenta to her fetus. Lasts a few weeks to a few months. No memory cells made. Can succumb to the disease later. 17 Artificial Passive Immunity Artificial passive immunity- Patients exposed to a serious pathogen maybe given a shot with preformed AB against the disease. The AB are found in the plasma of a person who has had the disease. The plasma is processed so that all the blood clotting proteins are removed forming serum. 18 When the Innate Immune System Goes Awry • Certain bacterial infection can induce an overwhelming inflammatory response. • Too many mast cells and phagocytes release huge cytokines and histamines. Too much fluid leaks from the capillary bed into the tissues. Blood pressure drops dangerously low and the tissues swells. Can be fatal. 19 When the Adaptive Immune System Goes Awry • Not all self-reactive lymphocytes are destroyed in development. Those that survive are suppressed. • Autoimmune diseases happen when certain suppressed lymphocytes are activated and attack the body’s own tissue. 20 A,B,O and AB Blood Groups and the Immune System 21 Antibodies and the Rh Factor The HIV Virus and Immunity • This is the HIV retro virus that causes AIDS. It contains RNA. • During replication, the RNA is transcribed to DNA. This process does not correct for transcription errors. This virus easily mutates. HIV Replication 24 Progress of AIDS 25 Helper T Cell and HIV virus A T-cell being infected by the HIV virus (blue particles) Created by: Carol Leibl Science Content Director National Math and Science