Biological and biochemical properties of a serum factor that stimulates splenic hemopoiesis in mice.

Some biological and biochemical properties of a distinct hemopoietic factor that stimulates splenic hemopoiesis in mice are described. This factor can be detected by measuring the increase in the number of in vitro hemopoietic colony-forming cells (CFCs) in the spleens of mice after transfer of serum from syngeneic donors that have been treated previously with the bacterial cell-wall components: lipid A or lipoprotein. Serum collected 5 min after the IV injection of lipid A contained almost no splenic hemopoiesis-stimulating factor (SHSF). The highest serum levels of the factor were found between 30 min and 3 h after lipid A was injected IV. The residual levels of lipid A or lipoprotein in the serum of treated mice were too low to account for their splenic hemopoiesis-stimulating effects. A component of SHSF in both post-lipid-A serum (PLAS) and postlipoprotein serum (PLPS) bound to concanavalin A (Con A)-Sepharose and could be eluted by alpha-methyglucopyranoside (0.05 M). Partial fractionation of PLAS using Con A-Sepharose and gel filtration (Sephacryl S-200) indicated that the SHSF glycoprotein had an apparent molecular weight of 30,000 daltons. SHSF was detected in serum in response to lipid A and lipoprotein, but this was separable (by gel filtration) from the major form of granulocyte-macrophage colony-stimulating factor (GM-CSF) in PLAS.