- An Immunoglobulin produced by B lymphocytes in response to a unique antigen. Each Ab molecule combines with a specific antigen to destroy or control it.
- All antibodies, except naturall antibodies (e.g., antibodies to different blood types), are created by B cells linking with a foreign antigen, typically a foreign protein, polysaccharide, or nucleic acid.
Antibodies neutralize or destroy antigens in several ways. They can initiate lysis of the antigen by activating the complement system, neutralizing toxins released by bacteria, coating (opsonizing) the antigen or forming a complex to stimulate phagocytosis, promoting antigen clumping (agglutination), or preventing the antigen from adhering to host cells.
An antibody molecule consists of four polypeptide chains (two light & two heavy), which are joined by disulfide bonds. The heavy chains from the complement-binding site, and the light & heavy chains form the site that binds the antigen. See Illus.;