Regulation of human peripheral blood erythroid burst-forming unit growth by T lymphocytes and T lymphocyte subpopulations defined by OKT₄ and OKT₈ monoclonal antibodies

To reexamine the influence that T lymphocytes have on the regulation of human peripheral blood burst-forming unit (BFU-E) proliferation in the absence of a statistically significant number of monocytes, very low numbers (3 to 10 x 10³/mL) of a null cell fraction highly enriched for BFU-E were cultured alone and in the presence of 5 x 10⁵ sheep erythrocyte-purified, autologous T lymphocytes in a methylcellulose culture system containing erythropoietin. T lymphocytes consistently enhanced the growth of BFU-E from the null cell fraction, as reflected in both their number and size. Irradiation of T lymphocytes prior to coculture with null cells markedly reduced this enhancement, strongly suggesting that T lymphocytes synthesize erythroid burst-promoting factors (BPA). To determine whether there were functional differences between the two major T lymphocyte populations as defined by OKT₄ (T helper/inducer) and OKT₈ (T suppressor/cytotoxic) murine monoclonal antibodies to stimulate the growth of BFU-E, both T cell subpopulations were isolated by negative (panning) or positive (fluorescence-activated cell sorting) selection and cocultured with null cells. No statistically significant differences emerged between unseparated, OKT₄⁺ and OKT₈⁺ T lymphocytes in their ability to stimulate the growth of BFU-E. Thus, these studies provide further evidence that T lymphocytes are a major population of BPA-producing cells and further that OKT₄⁺ and OKT₈⁺ T lymphocytes equally elaborate these factors.