IFN-gamma is not the only mediator of suppressed myelopoiesis produced by mononuclear cells from aplastic anemia patients.

Peripheral blood mononuclear cells (PBMC) from patients with aplastic anemia (AA) and healthy donors were compared with regard to their ability to produce soluble factors with inhibitory activity on in vitro granulopoiesis (GM-CFC). Although PBMC from AA patients produced enhanced levels of IFN-gamma as compared to controls, this lymphokine was found not to be the main inhibitor of in vitro granulopoiesis. Other, non-IFN related factors were potent inhibitors of both the mature and the immature precursors for GM-CFC, could act across the species barrier and were of low molecular weight. Also PBMC from healthy donors produced a non-IFN mediated GM-CFC inhibitory factor, but to a lesser degree and acting only on one type of myeloid precursors. The possible implications of these findings in relation to the etiology of AA will be discussed.