Development and application of a sensitive radioimmunoassay for human granulocyte-macrophage colony-stimulating factor able to measure normal concentrations in blood.

A radioimmunoassay (RIA) for human granulocyte-macrophage colony-stimulating factor (GM-CSf) was developed based on antibodies from rabbits immunized with glycosylated recombinant human (rh) GM-CSF. The antibodies are specific for human GM-CSF and do not crossreact with other human hematopoietic growth factors or mouse GM-CSF. The antibodies also react with nonglycosylated rhGM-CSF, so E. coli-derived rhGM-CSF can be assayed as well. The RIA has a measuring range of about 10 to 200 pg/mL. Normal blood was found to contain 13 to 24 pg/mL (95% limits) with a mean of 18.5 pg/mL (n = 34). Monoclonal antibodies against GM-CSF could remove GM-CSF from normal human serum, thus ensuring that the GM-CSF measured in serum is real and does not represent nonspecific reactivity with our polyclonal rabbit antibodies. While previously published methods have been unable to measure GM-CSF in human serum under normal conditions, our more sensitive RIA does confirm the presence of small amounts of GM-CSF in serum or plasma and can therefore be used to detect fluctuations of GM-CSF in health and in disease.