Cell free granulocyte colony inhibiting activity derived from human polymorphonuclear neutrophils

Human polymorphonuclears (PMN) or granulocytes (nonadherent: density > 1.070 g/cm³) were used to prepare a cell free colony inhibiting activity (CIA). Intact PMN, PMN conditioned media (serum free or serum containing) and supernatant from immediately lysed PMN equally reduced the numbers of spontaneous bone marrow (density < 1.070 g/cm³; depleted of PMN colonies and clusters. Addition of CIA reduced reproducibly colony and/or cluster numbers by 35 to 70%. CIA was heat labile being inactivated at 37°C. Daily additions of CIA reduced colony numbers even further; inhibition was dependent on [PMN] used to prepare CIA and on the potency of stimulation produced by colony stimulating cells (CSC). PMN from some patients with leukemia were inactive as inhibitors and did not condition media with CIA. All experiments were thereafter controlled by parallel assessment of supernatant of lysed PMN not demonstrating any CIA. CIA appears to be not only stored in PMN but released from viable, as well as degranulating PMN. Although not species specific, CIA was specific in its nontoxic action on CSC; colony forming cells and cell free colony stimulating activity were not affected. The influence of CIA on CSC could be reversed within 10 min, but not within 35 min of incubation. CIA may have possible physiologic relevance.