Towards large-scale purification of natural CSF-1 from human placenta tissue extracts

The monocyte-macrophage colony-stimulating factor (colony-stimulating factor 1) is characterized and partially purified from industrially processed human tissues for the first time. A five-step purification procedure using placenta tissue extracts furnished a 13,620-fold enrichment of biological activity. This procedure includes a "pilot" scale anion-exchange chromatography at pH 4.5, gel permeation, and lectin affinity separation followed by HPLC steps (hydrophobic interaction and C18 reverse-phase chromatographies). The purified bioactive material, which stimulates only monocyte-macrophage progenitors and mature cells, showed an Mr of 58,000-62,000 (gel filtration) and an isoelectric point of 3.8-4.0. The hydrophobicity of the molecule was low, and the biological activity was eluted at 50% acetonitrile on a C18 reverse-phase HPLC column. It was totally inactivated by 2-beta-mercaptoethanol reduction and heat treatment. Immunoprecipitation and neutralization of biological activity with specific anti-CSF-1 antibodies (not shown) demonstrated that this material was CSF-1. Step 5 of this protocol yielded two silver-stained bands on 12.5% SDS-PAGE: a major 55-kDa band (96%) and a minor 33-kDa band (4%). CSF-1 was detected exclusively in a band of 52-62 kDa by both Western immunoblotting and bioassays. Immunoaffinity techniques using antibodies directed against selective epitopes on the placental CSF-1 are now considered to purify this material to homogeneity. This approach to the mass production of natural CSF-1 from human tissue has advantages with respect to both the difficulty of post-translational processing of bioactive material in procaryotes and the cost of eucaryotic cell cultures.