Complete replacement of serum in cultures of murine primitive erythroid and multipotential progenitor cells: absolute requirement for spleen conditioned medium.

We describe a serum-free medium for the formation of erythropoietic bursts by murine bone marrow cells. Iscove's modified Dulbecco's medium supplemented with bovine serum albumin, iron-saturated transferrin, soybean phospholipids and cholesterol supported burst formation. The further addition of hemin increased burst numbers to above those obtained in serum-containing cultures. With or without hemin, a source of burst-promoting activity (BPA) (crude or partially purified spleen conditioned medium) and erythropoietin were essential. This system provides a sensitive assay for BPA. Of all colonies developing in these cultures, 16% were pure erythroid, 17% mixed erythroid/myeloid, 36% macrophage, 19% macrophage/basophil and macrophage/neutrophil, 9% basophil and 2% neutrophil.