Induction of tolerance against the Mls antigen in mice no need for Mls-bearing cells

Infusion of CBA mice with spleen cells from the H-2-compatible, but Mis antigen-incompatible, strain C3H leads to a specific reduction of the MLC reactivity of the host's lymphocytes. One explanation of the reduced reactivity could be that the specifically Mls antigen-responsive CBA T cells become exhausted by intense antigen stimulation or that the infused cells actively neutralize specifically responsive cells. In this investigation, we have shown that depletion of membrane Ig-positive cells from C3H × CBA spleen cell preparations strongly reduces their capacity to stimulate CBA lymphocytes in the MLC, indicating that the Mls antigen is expressed on B but not on T cells. However, such B-cell depleted cell preparations were fully capable of reducing the MLC response of CBA hosts. Cell preparations of spleen and lymph nodes exhibited high stimulatory and inhibitory effects. Thymic cells lacked both these characteristics, whereas bone marrow cells were weak stimulators but relatively strong inhibitors. The results support the proposal that the observed reduction of MLC reactivity is due to an active process of the injected cells. The cell type which is working as an inhibitor has not been clearly defined yet.