SOLUBLE FACTORS FROM PERIPHERAL-BLOOD T-CELLS OF PATIENTS WITH POLYCYTHEMIA-VERA STIMULATE NORMAL BFU-E

T cells and monocytes from patients with polycythemia vera (PV) were i solated and grown in culture. The conditioned medium was tested for th e presence of soluble factors that promote proliferation of erythroid colonies from the blood of healthy donors. We show that T cells from a il 14 PV patients that were examined secrete factor/s that stimulate t he proliferation of erythroid burst-forming units (BFU-E) in the absen ce of an external source of erythropoietin and BPA. Addition of cyclos porin A to the culture did not inhibit the production of this activity . The conditioned medium from monocytes of PV patients can also stimul ate normal BFU-E but to a much lesser extent than T-cell conditioned m edium. Such stimulation was not observed with control T cells or monoc ytes. We observed that the fraction of DR-positive T cells was signifi cantly higher in PV patients comparing to normal. These results sugges t that PV patients possess an abnormally high level of circulating act ivated T cells which may in turn be the source of the putative factor that facilitates uncontrolled erythroid differentiation.