Genetic restriction of cellular interactions that modulate in vitro erythropoiesis.

Immature erythroid precursors, assayed in vitro as BFU-E, express HLA-DR antigens that are distinct from the DR antigens expressed on lymphocytes. The growth of BFU-E in vitro is modulated by ill-defined factors elaborated by cooperating monocytes and T cells. Data from mouse studies suggest that factor elaboration is restricted genetically by Ia, and our data support this concept. In addition, we have shown that monocyte-dependent T cell-stimulating activity is limited by the presence of HLA-DR+ T cells. Whether the DR+ T cells suppress factor elaboration or alter BFU-E responsiveness to factor remains unknown. Nevertheless, the data suggest that HLA-DR antigens may play a role during in vitro hematopoiesis by restricting cell collaborations required to stimulate or inhibit growth.