Inflammation impairs IL-2R signaling in regulatory T cells

Abstract

Abstract Low-dose IL-2 is a promising therapy to boost Tregs in autoimmune diseases. Inflammation accompanying autoimmunity destabilizes Tregs to diminish their function. Here we explored how the extent of acute inflammation induced by LPS and poly(I:C) and of chronic inflammation induced by immunization with MOG and pertussis toxin (MOG/PT) affects IL-2R signaling in Tregs. IL-2-dependent pSTAT5 was significantly, but transiently, reduced in Tregs ex vivo from C57BL/6 mice exposed to LPS and MOG/PT, but not poly(I:C). LPS and PT, but not poly(I:C), induced inflammation through TLR4. IL-2-dependent pSTAT5 was also decreased in WT mice treated with only PT or in TLR4 Treg-conditional knockout mice treated with LPS. Thus, impaired IL-2R signaling is likely dependent on monocyte-derived inflammatory mediators through TLR4 signaling. LPS also decreased Treg proliferation as measured by Ki67 and increased CD69 expression. In contrast, these changes were not seen after treatment with poly(I:C) and MOG/PT, consistent with inflammation affecting Tregs independent of lower IL-2R signaling. When Tregs from LPS-treated mice were stimulated with IL-2 in vitro, pSTAT5 was induced, indicating that Tregs are not intrinsically unable to respond to IL-2. RNAseq of Tregs from LPS-treated mice revealed substantial changes in their transcriptome, suggesting a potential complex mechanism that impairs IL-2R signaling and other activities in Tregs in vivo. Our data support a model where inflammation lowers IL-2R signaling in Tregs by decreased IL-2 in the Treg microenvironment and causes other induced changes in Tregs to lower their function. Thus, a beneficial feature of low-dose IL-2 therapy may be to counteract negative effects of inflammation on Tregs.