Distinct populations of antigen-presenting cells are required for activation of suppressor and contrasuppressor T cells by type III pneumococcal polysaccharide

Type III pneumococcal polysaccharide (S3) coupled to spleen cells (S3-SC) has been shown to activate S3-specific Ts and Tcs in mice. Ts activation required I-J identity between carrier SC and Ts donors whereas I-A identity was required for Tcs activation. The carrier SC therefore presumably function as APC for Ts and Tcs activation by S3 since they are apparently not represented by APC present in the Ts and Tcs donors. The properties of the APC required for activation of S3-specific Ts and Tcs were determined by coupling S3 to various spleen cell subpopulations and assessing the ability of the various S3-SC populations to activate Ts and Tcs. The results indicate that Ts and Tcs are preferentially activated when S3 is presented on distinct cell types. S3-specific Ts were activated when S3 was coupled to plastic adherent cells. These cells are nonadherent to anti-Ig and nonfunctional in cyclophosphamide (Cy)-treated mice and their function is eliminated following treatment of cells with either anti-I-A or anti-I-J and C. In contrast, S3-specific Tcs were activated when S3 was coupled to anti-Ig adherent SC which bear I-A and the B cell marker J11d. These cells are functional in Cy-treated mice and their function is resistant to treatment with anti-I-J and C. Thus presentation of S3 on distinct cell types results in the preferential activation of T cells having opposing immunoregulatory function.