Connecting liver and gut: murine liver sinusoidal endothelium induces gut tropism of CD4+ T cells via retinoic acid.

UNLABELLED: Gut-activated T cells migrating into the liver can cause extraintestinal manifestations of inflammatory bowel disease. T cells acquire a gut-homing phenotype dependent on retinoic acid (RA) provided by intestinal dendritic cells (DC). We investigated whether liver antigen-presenting cells can induce gut tropism supporting an enterohepatic lymphocyte circulation. Priming of CD4(+) T cells by liver sinusoidal endothelial cells (LSEC) supported migration into gut and gut-associated lymphoid tissue. As observed for T cells primed by intestinal DCs, this gut tropism depended on α(4) ß(7) integrin and CC chemokine receptor 9 (CCR9) expression by LSEC-primed CD4(+) T cells. The induction of gut-homing molecules was mediated by RA, a derivate of vitamin A that is stored in large amounts within the liver. LSECs expressed functional retinal dehydrogenases and could convert vitamin A to RA. Conversely, the lack of signaling via the RA receptor prevented the expression of α(4) ß(7) integrin and CCR9 on LSEC-primed CD4(+) T cells, consequently reducing their in vivo migration to the intestine. Other liver antigen-presenting cells failed to support high expression of α(4) ß(7) integrin on CD4(+) T cells, thus, the potential to induce gut homing is restricted to LSECs. CONCLUSION: The capacity to promote gut tropism via vitamin A use is not unique for intestinal DCs but is also a feature of LSECs. Our data support the assumption that CD4(+) T cells can migrate from the liver to the gut as one branch of a postulated enterohepatic lymphocyte circulation.

Priming of CD4+ T cells by liver sinusoidal endothelial cells induces CD25low forkhead box protein 3- regulatory T cells suppressing autoimmune hepatitis.

UNLABELLED: Elucidating cellular mechanisms that maintain the intrahepatic immune balance is crucial to our understanding of viral or autoimmune liver diseases and allograft acceptance. Liver sinusoidal endothelial cells (LSECs) play an important role in modifying local immune responses to tolerance in major histocompatibility complex (MHC) I-restricted models, whereas their contribution in the MHCII context is still controversial. In an MHCII chimeric mouse model that excludes MHCII-mediated antigen presentation by professional antigen-presenting cells, we demonstrated that LSECs prime CD4(+) T cells to a CD45RB(low) memory phenotype lacking marker cytokine production for effector cells that was stable in vivo following immunogenic antigen re-encounter. Although these cells, which we term T(LSEC), had the capacity to enter lymph nodes and the liver, they did not function as effector cells either in a delayed-type hypersensitivity reaction or in a hepatitis model. T(LSEC) inhibited the proliferation of naïve CD4(+) T cells in vitro although being CD25(low) and lacking expression of forkhead box protein (FoxP)3. Furthermore, these cells suppressed hepatic inflammation as monitored by alanine aminotransferase levels and cellular infiltrates in a T cell-mediated autoimmune hepatitis model in vivo. CONCLUSION: T(LSEC) first described here might belong to the expanding group of FoxP3(-) regulatory T cells. Our findings strengthen the previously discussed assumption that CD4(+) T cell priming by nonprofessional antigen-presenting cells induces anti-inflammatory rather than proinflammatory phenotypes. Because recruitment of CD4(+) T cells is increased upon hepatic inflammation, T(LSEC) might contribute to shifting antigen-dependent immune responses to tolerance toward exogenous antigens or toward endogenous self-antigens, especially under inflammatory conditions.

Chemokine Transfer by Liver Sinusoidal Endothelial Cells Contributes to the Recruitment of CD4+ T Cells into the Murine Liver.

Leukocyte adhesion and transmigration are central features governing immune surveillance and inflammatory reactions in body tissues. Within the liver sinusoids, chemokines initiate the first crucial step of T-cell migration into the hepatic tissue. We studied molecular mechanisms involved in endothelial chemokine supply during hepatic immune surveillance and liver inflammation and their impact on the recruitment of CD4(+) T cells into the liver. In the murine model of Concanavalin A-induced T cell-mediated hepatitis, we showed that hepatic expression of the inflammatory CXC chemokine ligands (CXCL)9 and CXCL10 strongly increased whereas homeostatic CXCL12 significantly decreased. Consistently, CD4(+) T cells expressing the CXC chemokine receptor (CXCR)3 accumulated within the inflamed liver tissue. In histology, CXCL9 was associated with liver sinusoidal endothelial cells (LSEC) which represent the first contact site for T-cell immigration into the liver. LSEC actively transferred basolaterally internalized CXCL12, CXCL9 and CXCL10 via clathrin-coated vesicles to CD4(+) T cells leading to enhanced transmigration of CXCR4(+) total CD4(+) T cells and CXCR3(+) effector/memory CD4(+) T cells, respectively in vitro. LSEC-expressed CXCR4 mediated CXCL12 transport and blockage of endothelial CXCR4 inhibited CXCL12-dependent CD4(+) T-cell transmigration. In contrast, CXCR3 was not involved in the endothelial transport of its ligands CXCL9 and CXCL10. The clathrin-specific inhibitor chlorpromazine blocked endothelial chemokine internalization and CD4(+) T-cell transmigration in vitro as well as migration of CD4(+) T cells into the inflamed liver in vivo. Moreover, hepatic accumulation of CXCR3(+) CD4(+) T cells during T cell-mediated hepatitis was strongly reduced after administration of chlorpromazine. These data demonstrate that LSEC actively provide perivascularly expressed homeostatic and inflammatory chemokines by CXCR4- and clathrin-dependent intracellular transport mechanisms thereby contributing to the hepatic recruitment of CD4(+) T-cell populations during immune surveillance and liver inflammation.

Cytokine mRNA expression patterns in the disease course of female adolescents with anorexia nervosa.

Anorexia nervosa (AN) is a serious eating disorder characterized by extreme weight loss and abnormalities of the neuroendocrine and immune systems. Cytokines have been discussed to be involved in the pathomechanisms underlying cachexia. Therefore our study aimed at examining the mRNA expression pattern of tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin-6 (IL-6) and interleukin-10 (IL-10) in whole blood of 11 female AN patients and 10 age and sex matched normal weight control subjects using a sensitive quantitative polymerase chain reaction (PCR) method. We found a significant increase in TNF-alpha and IL-6 mRNA expression in anorectic patients at admission (mean BMI 14.8 +/- 1.3) when compared to controls. During follow-up, the expression of TNF-alpha mRNA remained significantly higher in formerly anorectic patients (mean BMI 18.7 +/- 0.5) while IL-6 mRNA expression decreased. We interpret our results as suggesting that TNF-alpha may contribute to metabolic abnormalities in anorexia nervosa even after goal BMI is achieved.

Failure of CD4 T-cells to respond to liver-derived antigen and to provide help to CD8 T-cells.

CD4 T-cell help is required for the induction of efficient CD8 T-cells responses and the generation of memory cells. Lack of CD4 T-cell help may contribute to an exhausted CD8 phenotype and viral persistence. Little is known about priming of CD4 T-cells by liver-derived antigen. We used TF-OVA mice expressing ovalbumin in hepatocytes to investigate CD4 T-cell priming by liver-derived antigen and the impact of CD4 T-cell help on CD8 T-cell function. Naïve and effector CD4 T-cells specific for ovalbumin were transferred into TF-OVA mice alone or together with naïve ovalbumin-specific CD8 T-cells. T-cell activation and function were analyzed. CD4 T-cells ignored antigen presented by liver antigen-presenting cells (APCs) in vitro and in vivo but were primed in the liver-draining lymph node and the spleen. No priming occurred in the absence of bone-marrow derived APCs capable of presenting ovalbumin in vivo. CD4 T-cells primed in TF-OVA mice displayed defective Th1-effector function and caused no liver damage. CD4 T-cells were not required for the induction of hepatitis by CD8 T-cells. Th1-effector but not naïve CD4 T-cells augmented the severity of liver injury caused by CD8 T-cells. Our data demonstrate that CD4 T-cells fail to respond to liver-derived antigen presented by liver APCs and develop defective effector function after priming in lymph nodes and spleen. The lack of CD4 T-cell help may be responsible for insufficient CD8 T-cell function against hepatic antigens.

Differential priming of CD8 and CD4 T-cells in animal models of autoimmune hepatitis and cholangitis.

UNLABELLED: The pathogenesis of autoimmune liver diseases is poorly understood. Animal models are necessary to investigate antigen presentation and priming of T-cells in the context of autoimmunity in the liver. Transgenic mouse models were generated in which the model antigen ovalbumin is expressed in hepatocytes (TF-OVA) or cholangiocytes (ASBT-OVA). Transgenic OT-I (CD8) or OT-II (CD4) T-cells specific for ovalbumin were adoptively transferred into TF-OVA and ASBT-OVA mice to induce in vivo priming of antigen-specific T-cells. T-cell migration and activation, as well as induction of liver inflammation, were studied. OT-I T-cells preferentially located to the liver of both mouse strains whereas no migration of OT-II T-cells to the liver was observed. OT-I T-cells proliferated in the liver of TF-OVA mice and the liver and liver draining lymph nodes of ASBT-OVA mice. OT-II CD4 T-cells were activated in spleen and liver draining lymph node of TF-OVA mice but not in ASBT-OVA mice. Transfer of OT-I T-cells led to histologically distinct inflammatory conditions in the liver of ASBT-OVA and TF-OVA mice and caused liver injury as determined by the elevation of serum alanine aminotransferase. CONCLUSION: An antigen expressed in hepatocytes is presented to CD8 and CD4 T-cells, whereas the same antigen expressed in cholangiocytes is presented to CD8 but not CD4 T-cells. In both models, activation of CD8 T-cells occurs within the liver and causes liver inflammation. The models presented here are valuable to investigate the priming of T-cells in the liver and their role in the development of autoimmune disease of the liver.