Type 1 Interferon signalling in human intestinal T cells.

Abstract

Intestinal immune homeostasis depends on the appropriate balance of pro-inflammatory and regulatory T cell activities which are themselves influenced by local mucosal signals. Dysregulation of these pathways leads to inflammatory bowel disease (IBD). Type 1 Interferon (T1IFN; IFNα/β), signalling via the phosphorylation of Signal Transduction and Activation of Transcription (STAT)1, is critical for innate protection against viruses but also has diverse effects on the immune system. They are potential local regulators of intestinal T cells. In mice, endogenous T1IFN ameliorates colitis by promoting regulatory T cell function. T1IFN has been used to treat IBD patients with limited success, but little is known about T1IFN in the human intestine. The aim of this work was test the hypothesis that T cells in the human intestine are modulated by intestinal factors such as T1IFN and that these responses are altered in IBD. A ‘Phosflow’ technique was developed to measure activation of key signalling molecules such as STATs at the single cell level. Responsiveness of human intestinal T cells to T1IFN was confirmed and increased expression of phosphorylated (p) STAT1 observed in CD4 T cells from IBD colonic tissue, irrespective of T1IFN stimulation. Increased pSTAT1 was associated with reduced expression of the STAT1 regulator SOCS1. Phosphorylation of STAT3 and STAT5 was not altered in IBD. Constitutive STAT1 phosphorylation was due in part to exposure to IFNβ. A potential role for T1IFN was supported by increased expression of Interferon Stimulated Genes (ISGs) by intestinal CD4 T cells in IBD and by the detection of endogenous IFNβ in fresh frozen sections of human colon. Addition of neutralising anti-IFNβ antibody to intestinal biopsy cultures led to an enhanced pro-inflammatory T cell cytokine profile and, in cells from healthy tissue, fewer IL10+ T cells. These data suggest that in health the endogenous T1IFN-STAT1 pathway supports a regulatory cytokine profile in human CD4+ intestinal T cells. There is evidence for dysregulation of this pathway in IBD, but the functional significance of this is less clear.