Studies on the pathogenesis of aplastic anemia in Thailand: evidence of immune-mediated mechanism.

The pathogenesis of aplastic anemia in Thailand was studied by using in vitro progenitor cells culture. In 37 patients who had active disease, the numbers of colonies derived from erythroid and granulocyte-macrophage progenitor cells (BFU-E and CFU-GM) were markedly decreased both in the blood and bone marrow as compared to normal controls. Co-culture of patients' cells with normal blood cells was performed in order to verify an immunologically mediated mechanism. In 8 of 26 patients, there were very low numbers of colonies both BFU-E and CFU-GM in the blood and bone marrow with significant suppression of colony formation in co-culture. Suppressor cells may have caused the aplasia in these patients. The rest had low colony formation and no suppression in co-culture. These patients may have absent or defective stem cells. None had normal colony formation. Therefore, aplastic anemia in Thailand may result mostly from defects involving the stem cells. Only some patients had cell mediated suppression of hematopoiesis as detected by co-culture.