Inhibition of human granulocyte-macrophage colony formation by interleukin 2-treated lymphocytes.

The effects of interleukin 2 (IL-2)-treated lymphocytes on human myeloid progenitors (CFU-GM) were studied. When peripheral blood mononuclear cells (PBMC) were cultured for 3 days with recombinant IL-2, they developed lymphokine-activated killer (LAK) activity against normal bone marrow cells, and also suppressed colony formation by CFU-GM. Suppression of CFU-GM was found to be mediated mainly by natural killer (NK) cells, and to a lesser degree by T cells according to the results showing that isolated NK cells and T cells exhibited strong and moderate suppressor function, respectively. Since the levels of LAK activity and of CFU-GM inhibitory activity were not parallel in each individual, inhibition of CFU-GM does not seem to be due to a direct lytic action by LAK cells. This possibility was supported by our finding that the supernatant of IL-2-treated PBMC contained factor(s) that inhibited CFU-GM colony formation.