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From: The Liver Meeting® 2008 (http://www.aasld.org/Pages/Default.aspx)

Enteric dendritic cells determine recruitment of mucosal T cells to the liver in Primary Sclerosing Cholangitis B. Eksteen1; S. M. Curbishley1; A. Aspinall2; D. H. 1 1. Liver Research Group, University Of Birmingham, Birmingham, West Midlands, United Kingdom. 2. Foothills Hospital, University of Calgary, Calgary, AB, Canada. Background and aims: Lymphocytes primed by dendritic cells (DCs) in the gut express the gut-homing receptors CCR9 and a4ß7 which recognise CCL25 and MADCAM-1 expressed in the intestine. In mice this programming is dependent on retinoic acid and subject to plasticity to allow the development of T-cells that can react to antigen at different anatomical sites. In humans tissue-specificity is lost in primary sclerosing cholangitis (PSC), an extra-intestinal manifestation of inflammatory bowel disease, when ectopic expression of MADCAM-1 and CCL25 in the liver promotes recruitment of CCR9 and a4ß7+ T cells to the liver. This led us to investigate whether the ability to imprint CCR9 and a4ß7 in humans is restricted to intestinal DCs and dependent on retinoic acid and thereby to determine whether T cells that infiltrate the liver in PSC are primed in the gut or liver.

Methods: DCs isolated from human gut, liver or portal lymph nodes were used to activate CD8 T-cells in the presence or absence of retinoic acid. Imprinting of CCR9 and a4ß7 and functional migration responses were determined and cross-over activation protocols used to assess plasticity of gut-homing.

Results: Gut-derived DCs imprinted functional CCR9 and a4ß7 expression on T-cells whereas DCs from other human tissues including the liver and portal lymph nodes of patients with PSC were unable to do so. Imprinting was retinoic acid-dependent and demonstrated plasticity.

Conclusions: Imprinting and plasticity of gut homing human CD8 T-cells requires primary activation or reactivation by gut DCs and is retinoic acid dependent. The inability of liver DCs to imprint gut-tropism implies that a4ß7+CCR9+ T cell that infiltrate the liver in PSC are primed in the gut and provides further evidence that gut-derived lymphocytes contribute to inflammation in the PSC liver.

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Factors responsible for MAdCAM-1 expression in human liver: potential targets for treatment of inflammatory bowel diseases (IBD) and its manifestations in the liver. E. Liaskou1; C. J. Weston1; B. Eksteen1; P. F. Lalor1; D. H. 1 1. Liver Labs, Institute of Biomedical Research, Birmingham, United Kingdom. MAdCAM-1 is a tissue-specific endothelial adhesion molecule which orchestrates immune responses in the gut by promoting the rolling and firm adhesion of lymphocytes on mucosal endothelium. Recent studies report the expression of MAdCAM-1 on liver endothelium in patients with primary sclerosis cholangitis and autoimmune hepatitis complicating inflammatory bowel disease (IBD). Understanding the factors that drive hepatic expression of MAdCAM-1 will thus elucidate the pathogenesis of these diseases. Liver endothelium expresses a cell surface enzyme, AOC-3 or vascular adhesion protein-1 (VAP-1), which is also an adhesion molecule. We have shown that activation of VAP-1 by substrates including methylamine, an aliphatic amine ingested from food and wine, drives NFkB-dependent activation of ICAM-1 and VCAM-1. In the current study we tested the hypothesis that VAP-1 enzyme activity can synergise with proinflammatory signals to drive MAdCAM-1 expression on liver endothelium.METHODS: We stimulated human sinusoidal endothelial cells (HSEC) and umbilical vein endothelial cells (HUVEC) with cytokines including TNFa (20ng/ml), rVAP-1 (50ng/ml) and methylamine (50µM) and then with combinations of TNFa plus methylamine. MAdCAM-1 expression was examined by ELISA, RT-PCR and Western blotting and function investigated in a flow-based adhesion assay, in which it was tested under physiological shear stress (0.05PA) the ability of lymphocytes expressing the MAdCAM-1 receptor a4ß7 to bind MAdCAM-1 induced in activated HSEC was tested. MadCAM-1 and a4ß7 were blocked with antibodies, P1 and ACT1 respectively.RESULTS: We detected for the first time levels of MAdCAM-1 mRNA and protein in untreated HSEC and HUVEC, though the encoded protein was inactive to support adhesion. However, treatment with methylamine and methylamine plus TNFa induced expression of functional MAdCAM-1 that supported significant levels of lymphocyte adhesion under flow. Blocking studies confirmed this adhesion was a4ß7-dependent.CONCLUSION: We report induction of ectopic MAdCAM-1 on human hepatic endothelium by the dietary amine constituent methylamine and suggest that methylamine in the portal blood of patients with IBD might act as an environmental factor to drive hepatic MAdCAM-1 expression resulting in the recruitment of disease-associated mucosal T cells in PSC.