ANTIGENIC VARIATION

ANTIGENIC VARIATION - ANTIGENIC VARIATION Antigens are the...

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Unformatted text preview: ANTIGENIC VARIATION Antigens are the part of an invader tht triggers an immune response in the host. Antibodies are the specific proteins produced in response to the presence of an antigen. When an antibody combines with the specific antigen that triggered its production, the antigen is somehow inactivated. Some pathogens can alter their surface antigens so that antibodies are no longer effective. Well know for doing this: Neiserria, Influenzavirus, Trypanosoma. PENETRATION INTO HOST CELLS' CYTOSKELETON By growing in host cells, bacteria can evade host defenses such as phagocytosis and antimicrobial substances. Not all bacteria enter host cells; in fact many of them cause damage without ever penetrating the cell. However, some bacteria do enter cells. They attach to the host cell by adhesins and this can trigger signals in the host cell that result in the taking in of the bacterium by the host cell. The mechanism involves the host cell cytoskeleton. Bacterial species that enter cells include Salmonella typhimurium, a cause of food poisoning, and Escherichia coli, which may cause severe diarrhea in children. These microbes attach to the plasma membrane of the host cell and cause changes in the membrane at the point of contact. The microbes produce proteins called invasins, that alter the cytoskeleton and cause the actin filaments of the cytoskeleton to take the bacterium into the cell. Once inside, these and others such as Shigella and Listeria may continue to use the actin filaments to move through the cytoplasm or even to move from cell to cell. Bacteria also may make contact with plasma membranes where cells join each other and use a glycoprotein called cadherin to move from cell to cell. ...
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ANTIGENIC VARIATION - ANTIGENIC VARIATION Antigens are the...

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