Complement

COMPLEMENT (from Latin complementum—supplement), addiment, Metchnikov's cytase, Buchner-Bordet alexin (see Alexin, Bordet-Gengou reaction, Immunity). The term complement was introduced by Ehrlich. The action of complement, according to Ehrlich, is enzymatic, conditioned by two groups: haptophoric and zymophoric. When the first group binds to the amboceptor, the second manifests its action, causing lysis. Complement capable of binding to the amboceptor, but devoid of the zymophoric group and consequently incapable of causing lysis, Ehrlich called a "complementoid." Neisser and Wechsberg named the phenomenon in which an excess of amboceptor not only fails to promote lysis but, on the contrary, inhibits it, the deviation of complement. This phenomenon is also called the Neisser-Wechsberg phenomenon. It can be observed when determining the bacteriolytic titer of sera, when undiluted or weakly diluted sera upon addition of complement do not produce bacteriolysis, while the same sera, being more diluted, lyse microbes. In hemolytic sera, this phenomenon is observed less frequently. Regarding the explanation of the complement deviation phenomenon, there is no consensus. The authors who discovered this phenomenon explained it by the fact that complement is bound by an excess of amboceptor present in the solution, due to which it is "deviated" from combining with the amboceptor already bound to the antigen. As a result, the complement turns out to be insufficient for dissolving the antigen (i.e., bacteria). However, this explanation was discarded after it was shown that complement does not bind to free amboceptor not combined with antigen. Thjøtta attaches primary importance in the phenomenon of complement deviation to specific inhibitory antibodies arising during immunization and combining with the antigen into complexes that adsorb complement. Pandit suggests that complement deviation is the result of the dissociation of the complement-amboceptor complex, occurring in the presence of an excess of amboceptor. Most likely, complement deviation is analogous to the zone phenomenon observed in other immunity reactions (agglutination, precipitation), when a reaction that takes place with diluted serum turns out to be negative with a more concentrated one (see Inhibition zone). The same zone phenomenon is observed, as is well known, upon mixing two colloids of opposite electrical signs. Lit.—see lit. to art. Alexin and the main manuals in lit. to art. Immunity.