Paracrine signalling mediated by cytokine secretion is essential for liver regeneration after hepatic resection, yet the mechanisms of cellular crosstalk between immune and parenchymal cells are still elusive. is released by immune cells and mediates strong hepatoprotective functions. However, it remains unclear whether IL-22 is critical for the crosstalk between liver lymphocytes and parenchymal cells during liver regeneration after partial hepatectomy (PH). Here, we found that plasma levels of IL-22 and its upstream cytokine, IL-23, are highly elevated in patients after major liver resection. In a mouse model of PH, deletion of IL-22 was associated with significantly delayed hepatocellular proliferation and an increase of hepatocellular injury and endoplasmic reticulum stress. Using Rag1 2/2 and Rag2 2/2 cc 2/2 mice, we show that the main producers of IL-22 post-PH are conventional natural killer cells and innate lymphoid cells type 1. Extracellular adenosine triphosphate (ATP), a potent danger molecule, is elevated in patients immediately after major liver resection. Antagonism of the P2-type nucleotide receptors, P2X1 and P2Y6, significantly decreased IL-22 secretion ex vivo. In vivo, specific inhibition of P2X1 was associated with decreased IL-22 secretion, elevated liver injury, and impaired liver regeneration. Conclusion: This study shows that innate immune cell-derived IL-22 is required for efficient liver regeneration and that secretion of IL-22 in the regenerating liver is modulated by the ATP receptor, P2X1. (HEPATOLOGY 2016;63:2004-2017 C ellular crosstalk, including secretion of cytokines and paracrine signaling via dangerassociated molecular patterns, is essential for liver regeneration after hepatic resection. The cytokine, interleukin-22 (IL-22), is released by immune cells and acts primarily on nonhematopoietic cells, such as epithelial cells, unlike most other cytokines, which target hematopoietic cells.(1) In the liver, IL-22 acts on hepatocytes and stellate cells and exhibits hepatoprotective properties by reducing liver fibrosis and ameliorating acute liver injury. (2)(3)(4)(5) In response to partial hepatectomy (PH), levels of IL-22 are elevated in the regenerating liver and exogenous administration of IL-22 as well as transgenic (Tg) expression is associated with improved outcome.(5) Yet, it remains unclear what the source and triggering factors of

In the multidrug resistance protein 2 (Mdr2) mouse model, low phospholipid bile instigates biliary epithelial injury, sterile inflammation, and fibrosis, thereby recapitulating disease mechanisms implicated in biliary atresia (BA) and primary sclerosing cholangitis. We hypothesize that T lymphocytes contribute to the biliary injury and fibrosis in murine sclerosing cholangitis (SC) and that they are susceptible to suppression by regulatory T cells (Tregs). In juvenile Mdr2 mice, intrahepatic CD8+ lymphocytes were expanded, and contraction of intrahepatic Tregs coincided with rising serum alanine transferase and alkaline phosphatase (ALP) levels between days 14-30 of life. Antibody-mediated depletion of intrahepatic CD8+ lymphocytes during that time reduced ALP levels and the expression of osteopontin (Opn), a pro-fibrogenic cytokine. Depletion of intrahepatic Tregs with anti-CD25 antibody between days 7-30 increased intrahepatic CD8+ T cells, Opn expression, and fibrosis. Conversely, expansion of intrahepatic Tregs with interleukin 2/anti-interleukin 2 immune complexes (IL-2c) downregulated hepatic expression of Opn and Tnf, reduced frequency of intrahepatic CD8+ lymphocytes, and diminished biliary injury and fibrosis. Treatment with IL-2c upregulated hepatic Treg expression of CD39, an ectonucleotidase capable of hydrolyzing pro-inflammatory adenosine triphosphate. In vitro, Tregs expressing CD39 suppressed the proliferation of hepatic CD8+ lymphocytes from Mdr2 mice more efficiently than those lacking CD39. In infants with BA, infiltration of interlobular bile ducts with CD8+ cells was associated with biliary expression of Opn and its transcription was negatively correlated with mRNA expression of Treg-associated genes. Conclusion: Hepatic CD8+ T lymphocytes drive biliary injury and fibrosis in murine SC. Their proliferation is controlled by hepatic Tregs through the purinergic pathway, which is responsive to IL-2c, suggesting that Treg-directed low-dose Il-2 treatment may be considered as therapy for SC.

Background and Aims During liver injury, quiescent hepatic stellate cells (qHSCs) transdifferentiate into proliferative and fibrogenic activated myofibroblastic phenotype (activated hepatic stellate cell; aHSCs) expressing smooth muscle α‐actin (αSMA) and platelet‐derived growth factor beta receptor (PDGFβR). Their interactions with gut‐derived bacterial lipopolysaccharide (LPS) are implicated in hepatic fibrogenesis. However, LPS can also attenuate fibrogenic characteristics of aHSCs. Approach and Results We examined molecular mechanisms of antifibrogenic effects of LPS on aHSCs in vitro and in vivo. Culture‐activated rat HSCs were exposed to 0‐100 ng/mL of LPS or its active component, diphosphoryl‐lipid A (DPLA), and parameters of fibrosis and inflammatory cytokines/chemokines were determined by qRT‐PCR, western, and immunohistochemical analyses. In vivo, HSCs were activated by repeated CCl4 administration to rats every 3 days for 3 or 8 weeks, then challenged with LPS (5 mg/kg; IP). HSCs were isolated 24 hours later, and fibrogenic/inflammatory parameters were analyzed. LPS induced phenotypic changes in aHSCs (rounding, size reduction) and loss of proliferation. LPS down‐regulated expression of αSMA, PDGFβR, transforming growth factor beta receptor 1 (TGFβR1), collagen 1α1 (Col1α1), and fibronectin while up‐regulating tumor necrosis factor alpha, interleukin‐6, and C‐X‐C motif chemokine ligand 1 expression. LPS did not increase peroxisome proliferation‐activated receptor gamma expression or lipid accumulation typical of qHSCs. DPLA elicited the same effects as LPS on aHSCs, indicating specificity, and monophosphoryl lipid A down‐regulated fibrogenic markers, but elicited very weak inflammatory response. LPS down‐regulated the expression of cMyb, a transcription factor for αSMA, and up‐regulated small mother against decapentaplegic (SMAD)7 and CCAAT/enhancer‐binding protein (C/EBP)δ, the transcriptional inhibitors of Col1α1 expression. In vivo LPS treatment of aHSCs inhibited their proliferation, down‐regulated PDGFβR, αSMA, TGFβR1, Col1α1, and cMyb expression, and increased expression of SMAD7, C/EBPα, and C/EBPδ. Conclusions In conclusion, LPS induces a unique phenotype in aHSCs associated with down‐regulation of key fibrogenic mechanisms and thus may have an important role in limiting fibrosis.

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