Human colony-stimulating factor (CSF-1) radioimmunoassay: Resolution of three subclasses of human colony-stimulating factors

The partial purification of human urinary CSF-1 to approximately 4 x 10⁶ U/mg protein from large volumes of human urine is described. Carrier-free iodination of the partially purified preparation and subsequent receptor binding and elution of the resulting ¹²⁵I-CSF-1 yielded ¹²⁵I-CSF-1, which, by several criteria, was free of contaminating ¹²⁵I-proteins. The ¹²⁵I-CSF-1 (approximately 4 x 10⁷ U/mg of iodinated protein) was biologically active and suitable for use in target cell binding studies. It was used to develop a RIA that specifically detects the human CSF subclass that stimulates macrophage production (CSF-1). This RIA, the CSF-1 radioreceptor assay, and the murine and human CSF bioassays were used in comparative studies of a variety of CSF preparations. Results of these studies indicate that there are at least three human CSF subclasses: CSF-1 which stimulates the formation of colonies containing macrophages by murine and human hemopoietic cells; another subclass stimulating the formation of colonies (possibly containing neutrophils, eosinophils, and macrophages) by human but not murine hemopoietic cells; and a third subclass that stimulates the formation of colonies (possibly containing neutrophils and macrophages) by both human and murine hemopoietic cells. Anti-human urinary CSF-1 antibody selectively prevented the development of human bone marrow colonies with the gross morphology of those stimulated by purified human urinary CSF-1, in cultures stimulated by a variety of CSF preparations. The average level of CSF-1 in the serum of 14 normal adult humans, as determined by RIA, was 174 ± 76 U/ml (approximately 40 pM).