Rh Antibodies and the Prozone Phenomenon

In 1942 Taylor, Race, Prior, and Ikin reported an anti-Rh serum which failed to agglutinate Rh- positive cells in saline suspension except when diluted.They thought that this prozone was due to antigen and antibody not being present in optimal proportions, and that the mechanism was similar to that of the zones that occur in pre- cipitation reactions.Wiener (1944) described incomplete Rh anti- bodies and their blocking effects, and considered that this type of antibody might be responsible for the prozones seen with Rh antisera.Subsequently, various other workers observed prozones with anti-human globulin sera, and Hubinont (1951) considered that these were due to lack of optimal proportions between antigen and antibody.Van Loghem (1950) also investigated the prozones of antiglobulin sera and considered that they might be due either to the presence of block- ing antibodies or to overdosage by excessive amounts of agglutinin, i.e., lack of optimal proportions.Van Loghem, Kresner, Coombs, and Fulton Roberts (1950) considered these two alternative explanations further, and described experiments to show that excess of agglutinin was the cause of the prozone in the particular antiglobulin reagent which they were studying.They suggested that, when agglutinin is present in high concentration, all the available antigen sites on the red cell surface become occupied by molecules of agglutinin, so that none are free to combine with molecules of agglutinin already attached to other cells, and the