Aberrant immunoregulatory control of B lymphocyte function in lepromatous leprosy

The capacity of peripheral blood mononuclear (PBM) cells from patients with leprosy to generate immunoglobulin-secreting cells in response to pokeweed mitogen (PWM) was evaluated by a reverse haemolytic plaque forming cell (PEC) assay. The PFC responses of PBM cells from patients with lepromatous (Lpr) leprosy were significantly higher (P < 0.01) than those of PBM cells from normal controls and patients with tuberculoid leprosy. Co-culture of T lymphocytes from normal donors with PBM cells from Lpr patients reduced the PFC response of these cells to the normal range. T4⁺-helper lymphocytes from Lpr donors did not induce supranormal responses to PWM by normal PBM cells enriched for B lymphocytes. T8⁺-suppressor lymphocytes from normal donors greatly reduced the response of cultures containing normal allogeneic B cells plus T4⁺ cells. Conversely, when T8⁺ cells from Lpr donors were cocultured with normal B cells plus T4⁺ cells, they failed to suppress the response to PWN. In summary, these studies have demonstrated abnormally high PWN-stimulated PFC responses by B lymphocytes from patients with Lpr leprosy. This aberration, in turn, is associated with a loss of regulatory function by T8⁺-suppressor cells in Lpr patients.