Suppression of erythroid-colony formation by lymphocytes from patients with aplastic anemia

To explore the possible role of cell-mediated suppression of erythropoiesis in acquired aplastic anemia, we studied the effect of peripheral blood lymphocytes from seven patients with aplastic anemia on erythroid-colony formation by normal human bone marrow in an in vitro plasma clot-culture system. Varying numbers of peripheral blood lymphocytes (0.5 to 6 X 10(5) cells) were cocultured with 6 X 10(5) normal bone-marrow cells in the presence of 2 IU of erythropoietin for seven days. Peripheral blood lymphocytes from five of the seven patients with aplastic anemia caused a 79 to 94 per cent reduction of erythroid-colony formation. Thus, at a peripheral blood lymphocyte concentration of 2 X 10(5) cells, the numbers of erythroid colonies formed (control vs. experimental) were 374 +/- 16 (S.E.M.) vs. 22 +/- 6, 48 +/- 4, 50 +/- 16, 80 +/- 4 and 27 +/- 3. These results suggest that some patients with aplastic anemia possess a population of lymphocytes capable of suppressing in vitro erythropoiesis.