Interleukin-4 receptor alpha chain and STAT6 signaling inhibit gamma interferon but not Th2 cytokine expression within schistosome granulomas.
Compared to wild-type (WT) mice, schistosome granulomas in Stat6 knockout (KO) mice lacked eosinophils and had Th1 features. Interleukin-4 (IL-4) acts through Stat6 in assisting Th2 cell development. The importance of Stat6 for Th2-cell development within schistosome granulomas had not been explored. Therefore we studied gamma interferon (IFN-gamma), IL-4, and IL-5 production in granulomas from Stat6 KO and WT mice. Dispersed granuloma cells from Stat6 KO and WT mice made similar amounts of IL-4 and IL-5. Only Stat6 KO granuloma cells released IFN-gamma. Granuloma T cells contained most of the IL-4, IL-5, and IFN-gamma mRNA and secreted these cytokines. In Stat6 KO mice, 16.6% of the granuloma cells were CD4(+). Of these, 10.7% stained for IFN-gamma and/or IL-4 by intracytoplasmic flow analysis. Few CD4(-) T cells stained positively. The IL-4-producing T cells did not stain for DX5 or with labeled alpha-GalCer CD1d tetramer, suggesting an absence of NK T cells. Thus, conventional Th cells in Stat6 KO granulomas produce IFN-gamma and Th2 cytokines. Stat6 limits IFN-gamma production but is unnecessary for Th2-cell development or localization within the granuloma.