B-cell suppression of antibody response to sheep red blood cells in mice of high- and low-responding genotypes.

CBA and C57B1 mice (high and low responders to sheep red blood cells, respectively) were injected intravenously with syngeneic lymph node, marrow, spleen, or thymus cells together with sheep red blood cells (SRBC), and the production of antibody-forming cells (AFC) was assayed in the spleen. Transfer of lymph node, marrow, spleen, or thymus cells led to a significant enhancement of immune responsiveness in low-responding C57B1 mice. In contrast, transfer of marrow, lymph node, or spleen cells to high-responding CBA mice was accompanied by a decline in AFC production. These effects were magnified if syngeneic cell donors had been primed with SRBC; suppression in CBA mice and stimulation in C57B1 mice were especially pronounced after transfer of SRBC-primed lymphoid cells. Pretreatment of CBA donors with cyclophosphamide in a dose causing selective B-cell depletion completely abrogated the suppression of immune responsiveness. A large dose (10⁷) of syngeneic B cells injected together with SRBC suppressed the accumulation of AFC in both CBA and C57B1 mice. No suppression of immune responsiveness was observed after transfer of intact thymus cells, hydrocortisone-resistant thymocytes, or activated T cells. We conclude that suppression of the immune response to SRBC is induced by B cells. At the same time, there is a possibility that the addition of “excess” B cells acts as a signal, triggering suppressor T cells.