Murine erythroid colony-promoting factor derived from thymocyte conditioned media.

It has been shown that murine thymocytes have some effects on the proliferation and differentiation of hemopoietic stem cells in mice. However, the precise mechanisms are not well known. We, therefore, investigated the effects of thymocytes on the proliferation of erythroid progenitors (CFUE) by using a normal murine syngeneic system. The addition of thymocytes to marrow cultures increased the number of CFUE colonies from marrow cells. Furthermore, conditioned medium prepared from thymocytes enhanced the in vitro colony growth of CFUE in the presence of erythropoietin. This enhancing factor(s) had a molecular weight of about 32,000 daltons and was heat stable at 70 degrees C for 30 min. We have concluded that murine thymocytes promote erythroid colony formation in vitro by producing an erythropoietic stimulating factor(s), although its detailed characteristics remain to be elucidated.