Human T Lymphocyte Subpopulations: Studies of the Mechanism by Which T Cells Bearing Fc Receptors for IgG Suppress T-Dependent B Cell Differentiation Induced by Pokeweed Mitogen

Abstract

The mechanism by which human T lymphocytes bearing receptors for IgG (T_G cells) suppress B cell differentiation promoted by pokeweed mitogen (PWM) and helper T_M cells was studied. In this model system, autologous T_G cells were shown to suppress via soluble factors released without detectable cell proliferation. In order to release these factors, T_G cells needed to interact with PWM in addition to their reaction with IgG immune complexes during the isolation procedure. Suppression occurred only when T_G cells were added early to mixtures of helper T and B cells cultured in the presence of PWM. B lymphocytes appeared to be resistant to suppression under a variety of experimental conditions. B cells “preactivated” by helper cells and PWM differentiated into plasma cells without any further help and were resistant to suppression by T_G cells. B lymphocytes re-isolated from 2-day cultures containing T_M cells, T_G cells, and PWM retained their capacity to differentiate into plasma cells when cultured with helper T cells and PWM. B cell differentiation induced by helper supernatants was resistant to activated T_G cells or their soluble factors. When T_M cells were preincubated with suppressor supernatants, their ability to induce B cell differentiation was reduced; in contrast, similar pretreatment of B cells had no effect on their differentiation. These results suggest that T_G cells can suppress the induction of polyclonal B cell differentiation by acting indirectly on helper T_M cells.