Partial characterization of colony stimulating activity from human leucocyte conditioned medium tested on human marrow cells.

Conditioned medium from normal human leucocytes was fractionated by gel filtration (Sephadex G 150) and affinity chromatography (Con A-Sepharose). On gel filtration, all colony stimulating activity (CSA) was eluted as a single peak with a molecular weight of 33.000 -- 41.000. Affinity chromatography revealed two separate peaks of colony stimulating activity, one lacking and the other having concanavalin A affinity (MW congruent to 44.000 -- 58.000). The properties of these two fractions are under investigation.