Human intrahepatic regulatory T cells are functional, require IL‐2 from effector cells for survival, and are susceptible to Fas ligand‐mediated apoptosis

Abstract

Regulatory T cells (Treg) suppress T effector cell proliferation and maintain immune homeostasis. Autoimmune liver diseases persist despite high frequencies of Treg in the liver, suggesting that the local hepatic microenvironment might affect Treg stability, survival, and function. We hypothesized that interactions between Treg and endothelial cells during recruitment and then with epithelial cells within the liver affect Treg stability, survival, and function. To model this, we explored the function of Treg after migration through human hepatic sinusoidal‐endothelium (postendothelial migrated Treg [PEM Treg]) and the effect of subsequent interactions with cholangiocytes and local proinflammatory cytokines on survival and stability of Treg. Our findings suggest that the intrahepatic microenvironment is highly enriched with proinflammatory cytokines but deficient in the Treg survival cytokine interleukin (IL)‐2. Migration through endothelium into a model mimicking the inflamed liver microenvironment did not affect Treg stability; however, functional capacity was reduced. Furthermore, the addition of exogenous IL‐2 enhanced PEM Treg phosphorylated STAT5 signaling compared with PEMCD8. CD4 and CD8 T cells are the main source of IL‐2 in the inflamed liver. Liver‐infiltrating Treg reside close to bile ducts and coculture with cholangiocytes or their supernatants induced preferential apoptosis of Treg compared with CD8 effector cells. Treg from diseased livers expressed high levels of CD95, and their apoptosis was inhibited by IL‐2 or blockade of CD95. Conclusion: Recruitment through endothelium does not impair Treg stability, but a proinflammatory microenvironment deficient in IL‐2 leads to impaired function and increased susceptibility of Treg to epithelial cell‐induced Fas‐mediated apoptosis. These results provide a mechanism to explain Treg dysfunction in inflamed tissues and suggest that IL‐2 supplementation, particularly if used in conjunction with Treg therapy, could restore immune homeostasis in inflammatory and autoimmune liver disease. (Hepatology 2016;64:138–150)

Pediatric autoimmune hepatitis shows a disproportionate decline of regulatory T cells in the liver and of IL-2 in the blood of patients undergoing therapy

“…However, intrahepatic Treg from autoimmune and inflamed livers had mostly a non-exhausted memory phenotype, expressed more functional relevant surface markers than peripheral blood Treg, and were functional in in-vitro studies [13, 14, 26]. The demethylated TSDR of the FOXP3 gene characterizes stable and suppressive Treg [23].…”

Clinical Potential of Regulatory T Cell Therapy in Liver Diseases: An Overview and Current Perspectives

“…We recently described intrahepatic Treg as predominantly effector memory lymphocytes with PD1 low , CD69 high phenotype (15) and expressing both hepatic homing CXCR3 and biliary tropic CCR6 chemokine receptors (14) (Figure 1). …”

Carcinoembryonic antigen‐related cell adhesion molecule 1 controls IL‐2‐dependent regulatory T‐cell induction in immune‐mediated hepatitis in mice

“…In this report, we analyzed the role of the immune regulator, CEACAM1, in a murine model of acute immune‐mediated liver injury and observed that it promotes IL‐2‐mediated signaling in CD4 + T cells, Treg induction, and Treg stability. The importance of IL‐2 for the survival and suppressive function of Tregs in patients with autoimmune liver diseases has been highlighted recently . Tregs constitutively express the high‐affinity receptor for IL‐2 (CD25; IL‐2Rα), which enables IL‐2 to control Treg homeostasis by STAT5‐mediated signaling .…”

“…Splenic single‐cell suspensions from ConA‐treated mice were either directly subjected to phosphorylated STAT5 (pSTAT5) labeling, or NPCs from livers were isolated and restimulated before pSTAT5 labeling in T cells . Detailed procedures for pSTAT5 labeling are described in Chen et al…”

“…T‐cell‐mediated liver diseases, such as autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), and primary sclerosing cholangitis (PSC), result from loss of hepatic tolerance and lead to chronic inflammation and liver fibrosis . In autoimmune liver disease, autoreactive CD4 + T cells induce immune‐mediate liver injury, such as in AIH.…”