Requirements for activation of contrasuppressor T cells by type III pneumococcal polysaccharide.

Either S3-coupled spleen cells (S3-SC) or soluble S3 activates two populations of regulatory T cells, T suppressor cells (Ts) and contrasuppressor T cells (Tcs). The latter cells function to mask the activity of Ts in unfractionated T cell populations, so that Ts can be detected only after removal of Tcs. Activation of Tcs by S3 may be required for induction of an antibody response to S3. This is suggested by the findings that Tcs are activated only by immunogenic doses of S3, that Tcs are not detectable in the spleens of mice tolerant to S3, and that (CBA/N X BALB/c)F1 male (xid) mice, which are genetically unresponsive to S3, do not develop Tcs after immunization with S3. Moreover, the kinetics of activation of Tcs by S3 closely parallels the kinetics of the antibody response to S3. Tcs have no detectable activity in the absence of Ts, indicating that these cells do not function as amplifier or helper T cells.