Serum Half-life and Organ Distribution of Radiolabeled Colony Stimulating Factor in Mice

Granulocyte-macrophage colony stimulating factor (GM-CSF) from mouse lung conditioned medium has recently been purified. This GM-CSF was radioiodinated using the chloramine T method, but dimethylsulfoxide was needed to prevent the loss of biological activity during the iodination. 125I-labeled GM-CSF was isolated from the reaction mixture by gel filtration and affinity chromatography with concanavalin A-Sepharose. One hour after intravenous injection of 125I-labeled GM-CSF almost 80% of the radioactivity was still localized in the serum. 125I-labeled GM-CSF was cleared from the blood of C57BL mice with a serum half-life of 7.3 +/- 1.3 hours. Six hours after intravenous injection 125I-GM-CSF appeared to be distributed throughout most of the tissues of C57BL mice. There was no selective concentration of 125I-labeled GM-CSF in the bone marrow, but levels in the kidney were three times higher than expected from the distribution of 125I-labeled mouse serum albumin. 125I detected in the blood 6 hours after injection of 125I-labeled GM-CSF was precipitable with trichloroacetic acid and bound to concanavalin A-Sepharose. 125I detected in the urine was not macromolecular and appeared to result from the degradation of 125I-labeled GM-CSF.