Control of primary IgM antibody responses to H-2 alloantigens by antigen-bearing live B lymphocytes.

Alloantigen-bearing (H-2d+) peripheral red blood cells, but not red cell-depleted H-2d+ spleen cells, induce primary IgM anti-H-2d plaque-forming cell responses. In this study it is reported that the primary antibody responses to H-2d+ peripheral red blood cells can be markedly suppressed by a subpopulation of H-2d+ spleen cells when they are injected simultaneously or a few days before injection of red blood cells. This suppression was antigen (H-2d)-specific, did not depend on T cells of either the donor or the recipient, and strictly required live donor cells. An energy-dependent action of the donor cell cortex and some proliferation of donor cells in the recipient seemed to be involved in the mechanism of suppression. The donor-suppressor cell type was largely present in the spleen but not in the bone marrow and thymus, and was present in the spleen of athymic nude mice. The suppressor cells displayed the properties of B lymphocytes: they adhered to the nylon wool but not to glass, were of relatively low density (rho less than 1.09), and were surface Ig+, Ia+, Fc receptor-positive but Thy-1-. H-2d+ suppressor-donor B lymphocytes might directly signal to antigen-specific recipient B cells competing with the signal provided by H-2d+ red blood cells for the B cell activation.