Interaction of peptidoglycans with anti-IgGs and with complement.

This report describes the interaction of peptidoglycan (Streptococcus group A, Staphylococcus epidermidis and Micrococcus lysodeikticus) with 2 serum mediator systems, namely with the anti-IgG system and with complement. The observation that the majority of rabbits hyperimmunized with A-variant streptococcal vaccine produced anti-group carbohydrate antisera containing anti-IgGs and antibodies directed to peptidoglycan suggested that the production of these 2 latter antibodies was related. This view was supported by the finding of a monoclonal 7S anti-IgG with antibody specificity for the pentapeptide of peptidoglycan as evidenced by inhibition of the coprecipitation of 7S anti-IgG with antigen-antibody complexes by the pentapeptide. Inhibition of the anti-idiotype reaction by the pentapeptide provided further evidence for the antibody specificity of 7S anti-IgG for peptidoglycan. When added to normal human sera all peptidoglycan preparations inhibited the hemolytic activity of the sera. Consumption of C3 in C2 deficient serum and consumption of C2 in normal serum indicated the activation of both known complement pathways. Activation of the classical pathway of complement was more efficient since 50 mug of peptidoglycan consumed approximately 70% of C2 per ml normal serum whereas more than 2 mg of the same preparations was required to inactivate 17-24% of C3 in C2 deficient sera. Each of the different peptidoglycan preparations consumed similar amounts of complement in all 20 sera tested. This finding suggested that activation of the classical complement pathway by peptidoglycan was not mediated by anti-peptidoglycan antibodies present in only 20-40% of normal human sera.