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 10#176 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 125l-CSF-1 yielded '25l-CSF-1, which, by several criteria, was free of contaminating 125I-proteins. The 1251-CSF-1 (approximately 4 x iO' 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.