General Features of Antigen – Antibody Reactions
Antigen-antibody reactions have the following general characteristics:
· The antigen-antibody reaction is specific. An antigen combines only with its homologous antibody and vice versa. However, the specificity is not absolute and cross reactions may occur due to antigenic similarity or relatedness.
· An entire molecule reacts and not fragments.
· There is no denaturation of the antigen or the antibody during the reaction.
· The combination occurs at the surface.
· The combination is firm but reversible. The firmness of the union is influenced by the affinity and avidity of the reaction. Affinity is the strength of binding of one molecule to another at a single site, such as the binding of a monovalent Fab fragment of antibody to a monovalent antigen. Avidity is the sum total of the strength of binding of two molecules to one another at multiple sites.
· Both antigen and antibody participate in the formation of agglutinates or precipitates.
· Antigens and antibodies can combine in varying proportions, unlike chemicals with fixed valence. Both antigens and antibodies are multivalent. Antibodies are bivalent. Antigens may have valencies up to hundreds.
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