THE HUMAN CYTOKINE-I-309 IS A MONOCYTE CHEMOATTRACTANT

The human cytokine I-309 is a small glycoprotein secreted by activated T lymphocytes and structurally related to a number of inflammatory cy tokines. To investigate the biological activities of I-309 protein, we produced a stable Chinese hamster ovary cell transfectant, CDI.10, wh ich constitutively secretes I-309 protein into culture supernatant. Af finity chromatography on a heparin-Sepharose matrix followed by revers e-phase HPLC was used to purify to homogeneity a glycoprotein doublet of 15-16 kDa from culture supernatant. Biochemical analysis showed the purified recombinant I-309 glycoprotein to be indistinguishable from the natural I-309 glycoprotein constitutively secreted by the T-cell l ine IDP2. Purified recombinant I-309 stimulated migration of human mon ocytes but not neutrophils when tested by in vitro chemotaxis assay. F urthermore, the purified protein transiently increased cytoplasmic fre e calcium concentration in human peripheral blood monocytes but did no t do so in lymphocytes or neutrophils. These results demonstrate that the I-309 gene encodes an inflammatory mediator that specifically stim ulates human monocytes.