Localization and Regulation of IFN-γ Production Within the Granulomas of Murine Schistosomiasis in IL-4-Deficient and Control Mice

Abstract

Schistosome granulomas from normal or IL-4-deficient C57BL/6 mice make little IFN-γ and show no Th1 polarization. This could signify that these granulomas have few cells capable of IFN-γ synthesis or that such cells are under tight control. Granulomas can make IL-10 and TGF-β, which can regulate IFN-γ synthesis. Using FACS analysis and ELISA, we explored the origin and regulation of IFN-γ in schistosome granulomas from both IL-4−/− and IL-4+/+ mice. FACS analysis of intracytoplasmic IFN-γ staining showed that some granuloma Thy1.2+ T cells (CD8+ and CD4+) express IFN-γ. Granulomas had NK1.1+ cells, but they appeared to produce little or no IFN-γ. Purified granuloma Thy1.2+ cells made IFN-γ in vitro, whereas isolated NK1.1+ lymphocytes secreted little even with rIL-12 stimulation. Culture of granuloma cells with blocking anti-IL-10 or anti-TGF-β mAb or with rIL-12 substantially increased T cell IFN-γ synthesis, particularly in the IL-4−/− animals. Cultured granuloma cells depleted of Thy1.2+ lymphocytes by Ab and C released no IFN-γ. It is concluded that granuloma IFN-γ comes from T cells, not NK cells. Also, this T cell-derived IFN-γ is subject to IL-10 and TGF-β regulation, which is particularly evident in IL-4−/− mice. Thus, the Th2 granuloma of schistosomiasis has large numbers of activated Th1 or Th0 lymphocytes that are under tight restraint.