Production of soluble suppressor factor by spleen cells from mice immunized with type III pneumococcal polysaccharide.

Supernatant fluid (SF) derived from spleen cell cultures, obtained from mice 16 hr after immunization with 0.5 microgram of Type III pneumococcal polysaccharide (SSS-III), suppressed the antibody response when SF was given (i.v.) 3 hr before immunization with SSS-III. Such suppression was antigen specific and could be reproduced by SF derived from cultures of T cells from mice immunized with SSS-III (0.5 microgram) or by SF derived from cultures of spleen cells from mice primed with a subimmunogenic dose of SSS-III (0.005 microgram). Adsorption of SF with SSS-III covalently bound to a Sepharose 4B column did not alter the ability of SF to suppress the SSS-III-specific antibody response. However, adsorption of SF with Ig+ (B) cells from mice immunized with 0.5 microgram SSS-III completely removed the suppressive activity. Significant (p less than 0.05) suppression of the antibody response was observed only when SF was administered (i.v.) 24 hr before to 24 hr after immunization with 0.5 microgram of SSS-III. These results suggest that suppressor T cells generated in response to SSS-III function by releasing a soluble factor(s) that binds to determinants on B cells rather than antigen; this soluble factor(s) acts directly on antigen-stimulated B cells or inhibits the induction of amplifier T cells.