CHARACTERIZATION OF NATURAL SUPPRESSOR CELLS IN HUMAN BONE-MARROW

Natural suppressor (NS) cells, which exert nonspecific suppressive act ivity in an unprimed manner, have been found in mouse, rabbit and monk ey bone marrow (BM), In the present study, we characterize NS cells in human BM. NS activity was found in a fraction of low density (1.055-1 .065 g/ml) BM cells that had been depleted of T cells, B cells, and mo nocytes, The NS activity was significantly decreased by the depletion of CD34(+) or CD33(+) cells but not CD56(+) cells, The NS activity was indeed detected in isolated CD34(+) cells and further enriched in CD3 4(+)CD33(+) cells, Hematopoietic progenitor cells committed to the mye loid lineage were also enriched in the CD34(+)CD33(+) cells, which sig nificantly correlated to the NS activity, From these findings, it is s trongly suggested that NS activity in human BM is exerted by the myelo id hematopoietic progenitors, Since cell-to-cell contact was not neces sary for the action, NS cells seemed to secrete soluble mediator(s). T ransforming growth factor-beta 1 and leukemia inhibitory factor were, however, not the candidates, based on experiments using neutralizing a ntibodies.