Helper function of human T cells with different affinity for Helix pomatia A hemagglutinin in a tetanus toxoid-induced B cell differentiation system.

T cells from human peripheral blood were enriched in T4+ cells by lysis of T8+ cells with the monoclonal antibody OKT8 plus complement. The T4+ subset was separated into 4 fractions differing in avidity for the lectin Helix pomatia A hemagglutinin (HP). The fractions were studied for their capacity to help autologous B cells to differentiate and mature into immunoglobulin (Ig) synthesis and secretion after activation with tetanus toxoid (TT) in vitro. To ensure the antigen specificity of induction, very low doses of TT (1-100 ng/ml) were used for activation of the lymphocytes, all obtained from previously sensitized donors. The T4+ cells with low avidity for HP (fractions HP-I and HP-II) exerted little help for B cell differentiation. Removal of these cells enhanced the helper function of the remaining T4+ cells, indicating that fractions HP-I and HP-II contained suppressor cells. In contrast, efficient B cell help was provided by T4+ cells with high avidity for HP (fractions HP-III and HP-IV). However, these fractions differed in the quality of help provided. Thus, while HP-III cells induced IgG secretion, HP-IV cells mainly induced IgM secretion. Moreover, while the Ig secreted after help from HP-III cells was TT-specific antibody, the Ig secreted by B cells in the presence of autologous HP-IV cells was polyclonal, probably reflecting induction of B cells differing in their responsiveness to signals provided by different types of T cells. The results indicate that T4+ cells vary in their stage of differentiation as seen by differences in expression of the HP marker and that differences in HP-marker expression appear to be associated with differences in cellular functions.