Coagglutination

Coagglutination, a non-specific agglutination of guinea pig erythrocytes described by Bordet and Gengou (1911), occurring in the case when these erythrocytes find themselves in a medium in which a precipitation reaction is taking place (see). Thus, if approximately 0.05 cm³ of immune guinea pig serum precipitating rabbit serum (antibody) and 0.1 cm³ of the latter serum (antigen) are introduced into 1 cm³ of defibrinated blood (erythrocytes) of a guinea pig, the guinea pig erythrocytes agglutinate. The mechanism of this phenomenon consists in the entrainment of guinea pig erythrocytes by the complex formed during the precipitation reaction (precipitinogen + precipitating serum). In this case, if the antibody acts on the antigen for a long time and the reaction between them manages to finish before the erythrocytes are added, then upon subsequent addition of erythrocytes coagglutination does not occur. For the demonstration of coagglutination it is better to use guinea pig erythrocytes and to take the precipitating serum in doses which do not give a coarse precipitate with its antigen. With the correct ratio of these doses coagglutination occurs instantaneously. Coagglutination is observed also in other serum reactions, for example in the agglutination of bacteria and the precipitation of colloids. Coagglutination can also occur in a living organism upon the sequential administration of a specific immune serum and antigen.