Expression of a 16,000 molecular weight antigen on human suppressor T lymphocytes

A human T-cell antigen with a molecular weight of 16,000 (p16) was expressed predominantly on suppressor T cells, while it had minimal representation on helper T cells. This p16 antigen was expressed on 37 ± 5% of ER⁺ blood T cells, and was co-expressed on all suppressor T lymphocytes recognized by a monoclonal antibody (OKT8). When ER⁺ T cells were fractionated on the basis of FcIgG receptor expression, p16 was detected on 62% of ER⁺FcIgG⁺ T cells (T_G ⁺ cells) and 26% of ER⁺FcIgG^- cells. The p16⁺ and p16^- T cells were physicially separated with a fluorescence-activated cell sorter and tested for their functional capability as inducer (helper) cells and suppressor cells in the terminal differentiation of pokeweed mitogen-stimulated B lymphocytes. Almost all of the helper cell activity was in the p16^- fraction. Suppressor cell function was analyzed by adding p16⁺ cells to a "helper cell combination" comprised of ER⁺ T cells plus B cells. Results in four individuals demonstrated that the p16⁺ cells could function as suppressor cells since they caused a 60 ± 3% decrease in plasma cell generation. In contrast, adding the p16^- cells to the "helper cell combination" further increased the plasma cell response by an additional 10 ± 17%. The helper cell population could be identified in both the FcIgG^- and FcIgG⁺ populations by fractionating these cells with respect to p16 antigen expression.