The Formation of Antibodies Against Hidden Determinants of Autologous IgG During Immunization of Rabbits with Staphylococcus aureus

Rabbits immunized with protein A‐producing staphylococci developed antibodies against hidden determinants of autologous IgG, as demonstrated by an indirect haemagglutination test using rabbit IgG combined with protein A (pAIgG) u antigen. Antibodies to pA‐IgG belonged to both the IgG and the IgM class of immunoglobulins. From inhibition experiments it was deduced that the actual antigenic determinant was located on the Fc part of IgG and made accessible when protein A combined with the IgG. Antibodies to protein A itself were probably not involved. The presence of antibodies to pA‐IgG in a serum was associated with the ability to precipitate protein A by double diffusion in agar gel (Ouchterlony analysis). This was valid for all materials investigated: rabbit antisera to protein A and to different strains of Staphylococcus aureus, sera from nonimmunized animals of ten species, and human myeloma IgGs.