T-cell effects on in vitro erythropoiesis: immune regulation and immune reactivity.

Optimal in vitro growth of BFU-E requires factors or burst promoting activities (BPA) in addition to erythropoietin. Our studies suggest that small numbers of DR-haploidentical T cells and monocytes present in plasma clot cultures of peripheral blood mononuclear cells can elaborate a BPA in situ. Various populations of normal T cells can augment or limit this activity. In addition, allosensitized "immune-reactive" T cells can inhibit this activity in both a genetically restricted and nonrestricted manner. With this in mind, it becomes important to consider that inhibition of BFU-E growth growth does not necessarily evoke lymphocytes reactive against BFU-E, but rather lymphocytes that can interfere with regulation of auxiliary cell function. Whether or not faulty immune regulation plays a role in "immune-mediated" aplasia remains to be determined.