Evaluation of radioimmunoassay and in vitro colony assay techniques for determination of colony-stimulating factor and inhibitory activity in murine serum and tissue

These studies have evaluated a newly developed radioimmunoassay (RIA) for the measurement of colony-stimulating factor (CSF) in murine serum and other biologic fluids. The routine in vitro agar gel bioassay for CSF is influenced by high molecular weight serum lipoproteins and low molecular weight tissue-derived materials that are inhibitory to colony formation. Studies with normal serum revealed that in all cases, the levels of CSF detected by the RIA were equal to or greater than levels measured by the bioassay. Dose curves with varying quantities of serum had linear responses in the RIA but not the colony assay. Using Sephadex G-150 chromatography, the murine serum was separated into CSF active and CSF inhibitory peaks as determined by bioassay. Evaluation of these fractions by RIA indicated that the assay was unaffected by the serum inhibitors. Likewise, experiments with tissue lysates indicated that the RIA was not influenced by the low molecular weight tissue inhibitors. Instead, the radioimmunoassay revealed low levels of CSF that were not detectable by bioassay. These observations indicate that the RIA is superior to the bioassay for the estimation of CSF in murine serum and other biologic materials.