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Transcript
Specific Responses All sorts of fun stuff What is this anyway? • Non-Specific defense has failed to stop the infection • Against particular pathogens • Exhibit memory Let’s get to know the bad guys: Antigens • A particular molecule, usually part of a pathogen or cancer cell • Also foreign antigens, those that the body does not produce • As well, self-antigens, which are those made by the body itself The process • We know our opponents, but how do we emerge victorious? • The first step is recognition • A particular antigen is recognized • Then comes the response • Takes 5-7 days to mount a response • More on this later • And then, we remember • The immune system remembers the antigens that it has previously seen • Reaction time significantly decreases the next time Microscopic guardian angels: Lymphocytes • Two types: • B Cells • T Cells • Both manufactured in red bone marrow • B cells mature in red bone marrow • T cells mature in the thymus How do they battle infections? • Each has a specific antigen receptor • B-cell receptor for B-cells • T-cell receptor for B-cells • Each has receptors that only combine with one type of antigen • Kind of like a lock and key mechanism • There exist specific B and T cells for any possible antigen we are likely to encounter during our lifetime! B-cells • They do antibody-mediated immunity • When they encounter an antigen, the receptor immediately recognizes it • B-cell gives rise to plasma cells • These produce specific antibodies • The antibodies have the same specificity as the B-Cell Receptor • The progeny (descendants) of the B-Cell that was activated become memory B-cells, and can recall that particular illness T-Cells • They do cell-mediated immunity • Do not immediately recognize an antigen directly • Must be brought to them by an antigen-presenting cell • Exist primarily as: • Helper T-Cells • Regulate specific immunity • Cytotoxic T-Cells • Take care of cancer cells and viral cells • Some also become memory T-Cells • Defend against the same virus or a same type of cancer The Clonal Selection Model • What happens when a B-Cell Receptor combines with an antigen? • Only the BCR that combines with the specific antigen clone will go on to divide and produce many new cells • Called antibody-mediated because most clones become the plasma cells that produce the specific antibodies • Also called humoral immunity • Antibodies are present in blood and lymph • Some progeny of the activated cells become B memory cells • When the infection has passed, plasma development halts Active and Passive Immunity • Active Immunity • An individual produces a supply of antibodies • Body produces antibodies as a result of infection, infection is stopped • Can be brought on by Immunization • Use of vaccination to expand cloning of B and T Cells • Most often are the pathogens themselves • Passive Immunity • Antibiotics are prepared for the individual to combat a disease • Short-lived because not made by their plasma cells • Breastfeeding promotes extended passive immunity after birth Structure of Antibodies • Y-shaped protein molecule with two arms • Has a “heavy” (long) polypeptide chain • Has a “light” (short) polypeptide chain • Have a constant region, located at the trunk of the Y • Variable regions form an antigen-binding site, specific to a specific antigen • Antibodies also called immunoglobulin (Ig) • Most typical is IgG, a Y-shaped molecule • These cross the placenta from a mother to a fetus • Also IgM antibodies, w2hich are pentamers • Five Y-shaped molecules Antigen-Antibody Combat Antigen-Antibody Combat • Several different ways • If antigens are part of a pathogen, antibodies may completely cover them • Called Neutralization • This reaction leaves a mixed clump of antigens and antibodies • Called an immune complex • These antibodies attract white blood cells that move in and finish the job