Human lymphocyte subpopulations involved in MLC and CML

Lymphocyte subpopulations from human peripheral blood were tested for their capacity to stimulate allogenic cells in MLC and for their ability to develop into cytotoxic cells in cell-mediated lympholysis (CML). By various cell separation experiments lymphocyte suspensions were depleted or enriched with respect to Fc receptor-bearing cells (detected as EA-RFC) and Ig-bearing cells. It was concluded that Fc receptor-bearing cells and Ig-bearing cells belong to different subpopulations. Furthermore, about 30% of the Fc receptor-bearing cells had T cell characteristics. The MLC stimulatory capacity was mainly confined to the Ig-bearing lymphocytes, and the Fc receptor-bearing cells and T cells exerted very little stimulation. Removal of Fc receptor-bearing cells strongly decreased the development of cytotoxic lymphocytes in CML. However, removal of Fc receptor bearing cells after MLC activation no longer affected cytotoxicity in CML. The activity in antibody-dependent lymphocytotoxicity was strongly decreased when Fc receptor-bearing cells were removed either before or after MLC activation. It was concluded that the cytotoxic precursor cells in CML bear an Fc receptor, which is either lost or blocked during MLC activation.