Antibodies in human sera to F(ab')2 fragments of monoclonal and polyclonal IgG.

F(ab')2 fragments of human, bovine and rabbit polyclonal IgG and of human IgG paraproteins of different subclass and light-chain type have been coupled to human red cells and used to detect "agglutinator' antibodies in normal and pathological human sera. The common occurrence of such antibodies in human sera and their heterogeneity in terms of specificity have been confirmed. No change in titre or specificity was found in monoclonal B cell proliferations. The possible significance of serum agglutinators is discussed.