Synergism between subpopulations of thymus-derived cells mediating the proliferative and effector phases of the mixed lymphocyte reaction.

The mixed lymphocyte reaction is characterized by proliferation and generation of specifically cytotoxic effector lymphocytes. These two phases of the mixed lymphocyte reaction have been shown to be mediated by distinct subpopulations of thymus-derived cells. The current investigation demonstrates that combinations of cells from thymus and lymph nodes of CBA mice exhibit synergism with respect to proliferation and effector cell production in response to Balb/c alloantigens. That is, the magnitude of the proliferative and effector phases of the mixed lymphocyte reaction exhibited by combinations of thymus cells and lymph node cells was greater than that given by equal numbers of the two cell types cultured separately. This cooperative interaction between lymphoid cell subpopulations in the mixed lymphocyte reaction parallels that which is responsible for the graftversus-host reaction. It is proposed, therefore, that the mixed lymphocyte reaction provides an in vitro model for the study of in vivo thymus cell interactions occurring in the graft-versus-host reaction.