Naturally occurring pepsin agglutinators in the serum of subhuman primates.

Antibodies directed against both human and infrahuman pepsin digested γ-globulin were present in a majority of the primate sera tested. The subhuman pepsin agglutinators paralleled previously described human pepsin agglutinators in respect to their wide distribution in normal sera, their specificity and cross-reactivity, and their immunochemical features. The pepsin agglutinators† at different primate levels appeared closely related. Among the subhuman pepsin agglutinators a subspecificity was described for a subhuman primate antigen. This finding suggested some limited differences between the subhuman pepsin agglutinators and the human pepsin agglutinators. Experimental immunization of four cynomologous monkeys failed to elicit or alter these serum reactants.