Abstract
INTRODUCTION: Innate lymphoid cells (ILC) have been implicated in the initiation of inflammation and fibrosis in mice. However, ILC have not been characterized in inflamed human liver tissue. METHODS: Human intrahepatic lymphocytes were isolated by mechanical digestion and phenotyped by flow cytometry. Conditioned medium from cultures of primary human biliary epithelial cells, stellate cells, fibroblasts and inflamed human liver tissue was used to model the effects of the inflammatory liver environment of ILC phenotype and function. RESULTS: All three ILC subsets were present in the human liver, with the ILC1 (CRTH2negCD117neg) subset constituting around 70% of intrahepatic ILCs. Both NCRpos (NKp44+) and NCRneg ILC3 (CRTH2negCD117pos) subsets were also detected. ILC2 (CRTH2pos) frequency correlated with disease severity measured by model of end stage liver disease (MELD) scoring leading us to study this subset in more detail. ILC2 displayed a tissue resident CD69+ CD161++ phenotype and expressed chemokine receptor CCR6 allowing them to respond to CCL20 secreted by cholangiocytes and stellate cells. ILC2 expressed integrins VLA-5 and VLA-6 and the IL-2 and IL-7 cytokine receptors CD25 and CD127 although IL-2 and IL-7 were barely detectable in inflamed liver tissue. Although biliary epithelial cells secrete IL-33, intrahepatic ILC2 had low expression of the ST2 receptor. Intrahepatic ILC2 secreted the immunoregulatory and repair cytokines IL-13 and amphiregulin. CONCLUSIONS: Intrahepatic ILC2 express receptors allowing them to be recruited to bile ducts in inflamed portal tracts. Their frequencies increased with worsening liver function. Their secretion of IL-13 and amphiregulin suggests they may be recruited to promote resolution and repair and thereby they may contribute to ongoing fibrogenesis in liver disease.