IL-4 AND IL-13 INDUCE LSK, A CSK-LIKE TYROSINE KINASE, IN HUMAN MONOCYTES

Lsk is a protein tyrosine kinase with homology to the COOH-terminal Sr c kinase (Csk). Unlike Csk that is ubiquitously expressed, Lsk has lim ited tissue distribution. Here we have examined the expression and reg ulation of Lsk and Csk in peripheral human monocytes. We have found th at Lsk mRNA and protein were not expressed in resting monocytes but we re induced by treatment with interleukin 4 (IL-4) or IL-13 but not by interferon gamma (IFN-gamma) or IL-2. In fact, IFN-gamma, but not IL-2 , efficiently blocked Lsk induction by IL-4 or IL-13. In contrast, Csk was constitutively present in human monocytes and was upregulated by IFN-gamma but not by IL-4 or IL-13. These results suggest that despite their structural similarities, Lsk and Csk may play distinct regulato ry roles in monocyte functions elicited by cytokines, with Lsk functio ning specifically within the context of a Th2-type immune response.