Equilibration of isoagglutinins of human group O serum.

Cross-reactive antibodies are shown to be responsibile for the difference in final levels of agglutination reached after dissociation of a centrifuged group O serum-erythrocyte mixture as compared with duplicate mixtures allowed toaggregate freely. This difference is seen only with certain group O sera, it is independent of complement, and it may be eliminated by absorption of the serum with A or B erythrocytes. The phenomenon is most likely the result of steric inhibition of smaller, cross-reactive antibodies in the aggregative system.