Development of a radioimmunoassay for human macrophage colony-stimulating factor (CSF-1)

Purified human urinary CSF-1 was used for production of polyclonal CSF antibodies in rabbits. The purified CSF was iodinated by a modified chloramine-T technique with retention of biologic activity. Dilutions of anti-CSF were reacted with 15,000 cpm of 125I-CSF in EDTA-phosphate buffer for 48 hr. Sheep antirabbit serum was added for 3 hr to precipitate the tracer-anti-CSF complex. A 1:1000 dilution of anti-CSF caused 60-90% precipitation of tracer; optimal conditions were observed with a 1:30,000 dilution. Linear displacement curves were obtained with 2-50 U of pure CSF-1. Related hormones did not cross-react in the assay; no displacement was seen with human GM-CSF, IL-1, IL-2, IL-3, EP, LH or FSH. Reactivity was also not observed with murine GM-CSF or IL-3. Ten normal human sera yielded CSF values of 91-138 U/ml in 5 assays. Urine values were 72-105 U/ml. When 32 U of pure CSF-1 was added to normal serum and urine samples, quantitative recovery was observed. Serial assays revealed a rise in serum and urinary CSF during marrow aplasia in a patient undergoing autologous BMT; CSF values returned to normal during the recovery phase. This sensitive and specific radioimmunoassay should prove useful in the further study of CSF-1 responses in vivo.