Erythropoiesis in steel mutant mice: effects of erythropoietin in vitro.

Adult SI/SI-d mutant mice have severe macrocytic, normochromic anemia. Moreover these animals are unresponsive to the stimulation of erythropoietin in vivo. By means of a bone marrow cell suspension culture system, the present investigation shows that in adult SI/SI-d marrow, there are cells capable of responding in vitro to erythropoietin in a normal fashion. Moreover, the erythropoietin present in SI/SI-d serum is biologically active in vitro without any prior biochemical modification. These observations support the suggestion that there is a defect in differentiation in the erythroid cell lines of SI/SI-d mice in vivo due to an abnormal hemopoietic microenvironment.