Effect of PHA-activated T cells on B-cell differentiation.

Recent studies indicate that human T cells expressing the T4 determinant are comprised of functionally distinct subsets. We investigated if activation of OKT4+ cells with the mitogen PHA affected their ability to regulate the proliferation and polyclonal differentiation of autologous B cells. OKT4+ cells were preactivated with PHA and then cocultured with autologous B cells in the presence or absence of PWM. B-cell proliferation and differentiation to immunoglobulin-secreting cells (IgSC) were assessed by [3H]thymidine incorporation and reverse haemolytic plaque assay, respectively. In the absence of PWM, the PHA-activated OKT4+ cells demonstrated radioresistant help and radiosensitive suppression of IgSC responses. Addition of PWM to cocultures of irradiated PHA preactivated OKT4 cells and autologous B cells resulted in further suppression of IgSC responses, suggesting that PWM activated yet another suppression mechanism. Addition of PWM caused diminished B-cell proliferation as well. These data demonstrate functional heterogeneity within the OKT4 subset, and suggest that the particular immunoregulatory activity displayed is influenced by the state and mode of activation of these cells.