Immunosuppressive effect of Staphylococcus aureus peptidoglycan on antibody response in mice

Immunosuppressive effect of an adjuvant, Staphylococcus aureus peptidoglycan, on the primary IgM antibody response in mice was studied with application of the hemolytic plaque assay. Peptidoglycan suppressed the IgM response to thymus-dependent sheep erythrocyte antigen when given intravenously before immunization. The effect of peptidoglycan and erythrocytes was both time and dose dependent. For the suppression, both the delay in the antibody response and overall decreased response were responsible. Peptidoglycan did not influence background counts of antibody-forming cells. Priming with subthreshold dose of erythrocytes did not overcome the suppression, although higher responses compared to unprimed animals were observed. Peptidoglycan did not suppress antibody response to thymus-independent antigens-lipopolysaccharide or high dose of erythrocytes. It is suggested that peptidoglycan-induced immunosuppression is mediated by a presently unidentified population of helper cells-macrophages or T lymphocytes.