Regulation of IgG responses by helper and suppressor T cells activated by pneumococcal capsular polysaccharides

Abstract

Type 2 antigens are usually unable to prime the helper T cells (T H) required for secondary IgG antibody responses. However, previous results from this laboratory indicated that low doses of the type 2 antigen polyvinylpyrrolidone (PVP) could activate T cells which provided help to PVP-primed B cells for the production of PVP-specific IgG antibody. Therefore, it was of interest to determine if other type 2 antigens may also be able to activate T H. Low doses of S19 or S3 (subimmunogenic for a primary IgM response) activated T H capable of providing help to S19- or S3-CRBC-primed B cells for a secondary IgG response. Higher doses of these antigens (optimally immunogenic for a primary IgM response) activated suppressor T cells (T S). Removal of these T S prior to transfer of T cells to recipient mice resulted in expression of T H function. Therefore, the preferential activation of T H versus T S was dependent on the dose of antigen used for priming. t h activated by low doses of S19 expressed Thy 1 and L3T4 and were antigen specific. In contrast to the ability of low doses of PVP to prime B cells for secondary IgG responses, low doses of S3 and S19 did not prime capsular polysaccharide-specific IgG memory B cells. High doses of S3 were able to prime B cells if T s precursors were first removed by treatment of mice with cyclophosphamide (Cy), whereas high doses of S19 did not prime B cells for secondary IgG responses in either Cy-treated or control mice. These results are discussed in relation to the general observations that type 2 antigens may not activate antigen-specific T H.