PRESENCE OF ANTIGEN‐ANTIBODY COMPLEXES IN ANTIALLOGENEIC AND ANTIXENOGENEIC SERA

SUMMARY Antilymphocyte sera (ALS), either allogeneic (for example, Lewis anti-August rat serum) or xenogeneic (the classic ALS), may retain the antigen used for the immunization of the animal producing the serum in the form of antigen-antibody complexes, at least when the animal is bled within the first 2 weeks following the last immunizing injection. Evidence for this has been obtained in vivo and in vitro. In vivo experiments showed that injection of Lewis anti-August serum to a normal Lewis rat can induce a delayed active immunization against the August strain. In vitro studies proved the presence of August antigens in the anti-August sera, by precipitation of the antigen-antibody complexes with 6 M urea, removal of the antibody by filtration, and demonstration that the filtrate specifically inhibits complement-dependent cytotoxicity of anti-August antibodies. The interpretation of a number of previous works on so-called passive enhancement of grafts or on various effects of ALS may have to be reconsidered on the basis of these findings.