Human growth factor for murine interleukin (IL)‐9 responsive T cell lines: co‐induction with IL‐6 in fibroblasts and identification as LIF/HILDA

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Abstract
Two mouse helper T cell clones that proliferate in response to murine interleukin (IL)‐9 could also be grown in conditioned medium of stimulated human connective tissue cells. The activity was not due to known T cell growth factors including human IL‐9, which is not effective on mouse cells. This growth‐stimulatory activity for TS1 cells (GATS) was co‐induced with IL‐6 on normal fibroblasts and certain sarcoma cell lines stimulated with IL‐1, double‐stranded RNA, virus or phorbol ester. However, the conditions for optimal induction and the kinetics of production were found to be different for IL‐6 and GATS. GATS from phorbol ester‐stimulated human hepatosarcoma cells co‐purified with IL‐6, but could be separated from it by subsequent cation‐exchange fast‐protein liquid chromatography and reverse‐phase high‐performance liquid chromatography. Homogeneous tumor cell‐derived GATS was a 25‐kDa protein on sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, whereas IL‐6 produced by these cells appeared in its 23‐kDa form. Pure GATS was found to be inactive in the B cell hybridoma growth assay for IL‐6. Finally, GATS was identified by NH2‐terminal sequence analysis of the mature protein as leukemia inhibitory factor or human interleukin for DA cells (LIF/HILDA). The effect of LIF/HILDA on T cells was not mediated by IL‐2, IL‐4 or IL‐9 production. Since this cytokine has not previously been reported to act on T cells, further investigation of its role in T cell activation should be taken into consideration.