Colony-stimulating factor (CSF) radioimmunoassay: detection of a CSF subclass stimulating macrophage production.

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Abstract
Colony-stimulating factors (CSF) stimulate the differentiation of immature precursor cells to mature granulocytes and macrophages. Purified 125I-labeled murine [fibroblast] L cell CSF was used to develop a radioimmunoassay RIA that detects a subclass of CSFs that stimulates macrophage production. Murine CSF preparations that contain this subclass of CSF compete for all of the CSF binding sites on anti-L cell CSF antibody. With the exception of mouse serum, which can contain inhibitors of the bioassay, there is complete correspondence between activities determined by RIA and those determined by bioassay. The RIA is slightly more sensitive than the bioassay, detecting approximately 0.3 f[femto]mol of purified L cell CSF. It can detect this subclass of CSF in chickens, rats and humans. In the mouse, the subclass is distinguished from other CSFs by a murine cell bioassay dose-response curve in which 90% of the response occurs over a 10-fold (rather than a 100-fold) increase in concentration, by stimulating the formation of colonies containing a high proportion of mononuclear (rather than granulocytic) cells, and by certain physical characterics.