Soluble cytokine receptors are present in normal human urine.

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Abstract
Affinity chromatography of crude human urinary proteins on either human rIL-6, human rIFN-.gamma., or anti-IFN-.gamma.-R mAb yielded the two respective soluble receptors in significant quantities. A single sequence of 30 amino acid residues was obtained by NH2-terminal microsequencing of the protein peak purified in tandem by affinity chromatography on an IL-6 column and reversed-phase HPLC. This sequence was identical to the predicted NH2-terminal sequence of IL-6-R as previously reported. Analysis of the eluted proteins from both IFN-.gamma. and anti-IFN-.gamma.-R columns by inhibition of solid phase RIA, ELISA, SDS-PAGE, and Western blotting proved the existence of soluble IFN-.gamma.-R in normal urine. Our finding, together with the already known presence of urinary TNF binding proteins and a soluble IL-2-R both in plasma and in urine, indicates that release of soluble cytokine receptors into body fluids is a general phenomenon that occurs under normal physiological conditions.