Large granular lymphocytes have a promoting activity on human peripheral blood erythroid burst-forming units

Peripheral blood mononuclear cells were fractionated according to the expression of a variety of surface markers, and the fractions obtained were tested for erythroid burst-forming unit (BFU-E) colony formation. BFU-Es were detected in the HLA-DR+ non-T cell fraction, but gave rise to optimum colony numbers only in the presence of a nonadherent, relatively radioresistant cell. This accessory cell was found among the HLA-DR- non-T, non-B cells, a fraction that was particularly enriched in large granular lymphocytes (LGLs). Experiments carried out to assess directly the surface markers of the accessory cell revealed an FcR+, OKM1+, Leu 7+, Leu 11+, OKT4-, OKT8- surface phenotype, which is consistent with that of the majority of LGLs. Peripheral blood LGLs, purified by Percoll density gradient, proved very efficient in promoting optimal BFU-E colony formation. All of these results indicate that LGLs have a potent erythroid burst-promoting activity. Such activity is probably mediated through the release of soluble factors, as shown by the observation that LGL culture supernatants were as effective as LGLs in sustaining colony formation.