Enhancement by Irradiated T Cells of Human Plasma Cell Production: Dissection of Helper and Suppressor Functions in Vitro

The addition of irradiated T-enriched lymphocytes to B cell-enriched fractions of human peripheral blood or to unseparated mononuclear cells stimulated the differentiation of plasmacytoid cells in culture with pokeweek mitogen beyond the synergy obtained by the addition of unirradiated T cells. This stimulation was observed in both the proportion and absolute number of plasmacytoid cells recovered from the cultures, and in the amount of IgM detected in culture supernatants by a hemagglutination inhibition assay. Irradiation-induced enhancement was observed with normal and hypogammaglobulinmic T cells, but not with monoclonal T cells from two patients. Inactivation of T cells by heating or by repeated freezing and thawing did not produce the same effects as did irradiation. These data suggest that cell-mediated suppressor function in man is selectively radiosensitive, while helper activity is not. Irradiation may be a useful method for the functional isolation of helper cells and for the manipulation of the balance between suppressor and helper cell activities.