The formation of antigen-antibody complexes is useful in the response to infectious organisms or foreign substances because they remove the infectious agent from the body. Protective methodology of binding antibodies to antigens is accomplished by agglutination, opsonization, neutralization, antibody-dependent cell-mediated cytotoxicity, and the activation of complement.
• Agglutination generates antibodies that clump together antigens, making them easy to ingest by phagocytes.
• Opsonization coats the antigen with antibodies to make it easy for phagocytic cells to ingest and for lysis.
• Neutralization blocks antigens from attaching to targeted cells, thereby neutralizing the antigen.
• Antibody-dependent cell-mediated cytotoxicity coats the foreign cell with antibodies. Nonspecific immune cells then destroy the foreign cell from the outside. This is used for organisms that are too large for phagocytic cells to ingest.
• The activation of complement is used when infectious agents are coated with reactive proteins that cause IgG and IgM antibodies to attach to the agent, causing lysis of the cell membrane and resulting in ingestion by phagocytes.
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