Primary murine immunoglobulin M responses to certain pneumococcal capsular polysaccharides consist primarily of anti-pneumococcal cell wall carbohydrate antibodies.

The antibody induced in mice immunized with a vaccine preparation of type 6 (Danish type 6A) pneumococcal capsular polysaccharide (S6) reacted with several chemically disparate pneumococcal capsular polysaccharides. Equivalent numbers of plaque-forming cells were observed when sheep erythrocytes coated with either S6, type 19 pneumococcal capsular polysaccharide (S19), or the pneumococcal cell wall carbohydrate (PnC) were used to detect the response to S6 or to S19. The addition of exogenous PnC to the plaquing mixtures of spleen cells from S6-, S19-, or PnC-immunized mice inhibited the appearance of most (greater than or equal to 85%) of the plaque-forming cells. Furthermore, the addition of monoclonal antibody specific for the dominant (TEPC 15) idiotype of anti-phosphorylcholine (a component of PnC) antibodies also inhibited the appearance of most of the plaque-forming cells. A suppressed S19 response was induced by priming mice with a low dose of S19 or PnC 3 days before immunization with an optimal dose of S19 (low-dose paralysis). These results demonstrated that most, if not all, of the antibody stimulated by these preparations of S6 and S19 was actually induced by and was specific for PnC.