Suppression of IgM responses to type III pneumococcal polysaccharide by lipopolysaccharide (LPS).

Lipopolysaccharide (LPS) suppressed the primary IgM response of mice to Type III pneumococcal polysaccharide (S3). LPS and S3 had to be given together in order for maximum suppression to occur and suppression was not due to a change in the time of the peak response in mice which received LPS. Suppression was not due to an effect of LPS on T cells since S3 responses of nude mice were suppressed by LPS. LPS did not suppress S3 responses of C₃H/HeJ mice and base hyrolysis of LPS destroyed the suppressive effect, i.e., suppression was dependent of B cell mitogenic activity of the LPS. The suppressive effect of LPS was presumably directed against virgin B cells since LPS did not suppress the S3 response of primed mice and did not suppress the development of IgG memory responses to S3.