| Abstract: | Interferons (IFN) have been shown to suppress the proliferation of human erythroid progenitors (BFU-E, CFU-E) in vitro. We have previously demonstrated that the inhibition of erythroid colony formation by gamma-IFN in vitro is mediated, in part, through the activation of monocytes and T-lymphocytes. In order to examine the mechanism(s) underlying the inhibitory action of one type of recombinant alpha-IFN (alpha-2-IFN) on erythropoiesis, the effect of different doses (80-10,000 U) of alpha-2-IFN on erythroid colony formation by normal human bone marrow cells in the presence or absence of monocytes and/or T cells was studied. The addition of alpha-2-IFN to whole marrow caused the suppression of BFU-E (10%-68%) and CFU-E (5%-75%) in a dose-dependent fashion. This inhibition occurred with the direct addition of alpha-2-IFN to culture plates but not with brief preincubation of marrow cells with alpha-2-IFN followed by washing of the cells. By contrast, brief exposure of marrow cells to gamma-IFN resulted in significant suppression of erythroid colony formation. The inhibitory action of alpha-2-IFN was not influenced by erythropoietin. Removal of monocytes and/or T cells prior to the addition of alpha-2-IFN failed to significantly reduce the suppressive effects of this molecule (BFU-E: 21%-66%; CFU-E: 20%-83%). Coculture of purified monocytes or T-lymphocytes preexposed to alpha-2-IFN with autologous bone marrow cells did not cause suppression of erythropoiesis; monocytes or T cells similarly treated with gamma-IFN, however, inhibited autologous BFU-E and CFU-E in vitro. These results demonstrate that, unlike gamma-IFN, the inhibitory effect of alpha-2-IFN on erythroid colony formation in vitro is not mediated to any significant degree through monocytes and T-lymphocytes. The suppressive effect of alpha-2-IFN occurs either directly at the erythroid progenitor(s) level and/or through accessory cell(s) other than monocytes and T cells. |
