Soluble factor(s) released by the PF‐382 T‐cell line enhances the stimulatory effect of monocytes on the BFU‐E growth

PF‐382 is a human T‐cell line that has been shown to elaborate factors that modulate normal hemopoiesis in vitro. In the present study we report that this cell line constitutively releases in both serum‐containing and serum‐free supernatants a potent enhancer of BFU‐E growth. The factor(s), partially purified by gel filtration, is a heat‐stable molecule(s) degradable by trypsin and 2–mercaptoethanol treatments, equally active on bone marrow and peripheral blood erythroid progenitor cells, but not on CFU‐GM. Unlike other sources of BPA, this stimulatory factor(s) exerts its effect in the presence of mononuclear adherent cells. In fact, the addition of conditioned medium obtained by 48 hr preincubation of isolated monocytes with 10% PF–382 supernatant (M‐CM2) or the concomitant addition of supernatant from PF–382 cells (PF–382–CM) and from unstimulated monocytes (M‐CM1) are capable of fully replacing the presence of monocytes in the BFU‐E assay. Since the independent addition of PF‐382‐CM or of M‐CM1 is devoid of stimulatory function, we suggest that the PF‐382 derived BFU‐E growth inducer, which differs from IL–1, IL–3, IL–4, GM and G‐CSF, exerts its activity “via” a synergistic mechanism with a monokine.