Anti-globulin antibodies detecting hidden gamma G antigens: characterization of the "pepsin site" by different immune antisera.

The antigenic region of human γG-globulin revealed by pepsin digestion has been studied by means of four different pepsin agglutinator' (PA) containing sera. Two of these were naturally occurring' agglutinators found in human and subhuman (baboon) sera respectively. The other two were heteroimmune antisera produced by the immunization of rabbits with human and baboon F(ab′) fragments. All of the PAs were agglutinating but not precipitating. Each PA reacted specifically with γG and γG immunoglobulins as determined by testing with isolated human myeloma proteins. One of the rabbit PAs (RAHPA) reacted with both reduced and unreduced pepsin fragments in contrast to the other agglutinators. In addition, different reaction patterns were evident when the PAs were tested with a panel of pepsin digested primate γG-globulins. The general trend of the data suggested that a similar antigen was being detected by the four PAs. Further, it was evident that a limited degree of heterogeneity existed within the human `pepsin site' and between similar regions in higher primates.