Modulation of in vitro BFU-E growth by normal Ia-positive T cells is restricted by HLA-DR

The in vitro growth of immature erythroid precursors, assayed as burst forming units (BFU-E), can be enhanced by co-culturing with normal T cells. The growth enhancing effect of normal T cells, however, was shown to be the outcome of at least two functionally distinct subpopulations, one that enhances burst formation and one that limits it. It appears that the T cell population limiting growth enhancement of the erythroid precursors expresses 'Ia-like' antigen (Ia+) because treatment of T cells with anti-Ia antibody and complement significantly increased the ability of the remaining T cells to stimulate antologous BFU-E growth. As BFU-E also seem to express Ia, the inhibiting effect of certain T cells on BFU-E growth may involve the Ia molecule. We show here that the inhibitory effect of Ia+ T cells on BFU-E growth is genetically restricted to cell combinations which are phenotypically identical for at least one HLA-DR (Ia-like) antigen.