Autoaggression of FOXO1lowCXCR6hiCD8+ T cells causing liver pathology in NASH

Question:

During chronic liver inflammation an imbalanced immune system causes liver damage. For chronic infectious inflammation it is known that the adaptive immunity drives liver pathology. But how liver damage is induced during chronic sterile inflammation like non-alcoholic steatohepatitis (NASH) is completely unknown. Appropriate integration of extracellular factors into a transcriptional network in CD8⁺ T cells is indispensable to control effector function avoiding immune pathology. In the liver CXCR6⁺CD8⁺ T cells express high levels of effector molecules like GzmB and are important for tissue homeostasis. Here we identify FOXO1-activity in CXCR6⁺CD8⁺ T cells as critical regulator of CXCR6 expression and effector function during chronic sterile inflammation in NASH.

Methods:

RNA-seq, flow cytometry and cytotoxicity assays were performed to study immunity of CXCR6⁺CD8⁺ T cells and its dependence on FOXO1 in vitro and ex vivo studies. Murine model of non-alcoholic steatohepatitis (NASH) was used to explore FOXO1-dependent T cell immunopathology.

Results:

RNA-seq analysis of CXCR6⁺CD8⁺ T cells of the liver from NASH mice compared to CXCR6⁺CD8⁺ T cells from WT mice revealed strong upregulation of effector and inhibitory molecules with FOXO1 as the central transcription factor. Flow cytometric analysis confirms a FOXO1^lowCXCR6⁺GzmB^highCD69⁺PD1⁺CD8⁺ T cell population that was highly and specifically increased in the liver of NASH mice. We discovered IL-15 and IL-21 as critical cytokines downregulating FOXO1 accompanied with an increase of CXCR6⁺CD8⁺ T cells. Treatment of NASH mice with an anti-CD122 antibody abrogated the generation of CXCR6⁺GzmB^highCD8⁺ T cells associated with a strong amelioration of liver disease. Mechanistically, hepatocytes were killed in vitro by CXCR6⁺CD8⁺ T cells with lower FOXO1 activity through an MHC class I independent but ICAM-LFA1 dependent manner. Inflammatory levels of TNFa were critical to upregulate ICAM and to facilitate formation of an immunological synapse of hepatocytes with CXCR6⁺CD8⁺ T cells even in the absence of antigens. Since ICAM cluster were higher in NASH mice, we assume that increased effector function in CXCR6⁺ CD8⁺ T cells in the absence of FOXO1-control caused antigen-independent hepatic immunopathology.

Conclusion:

Our results provide evidence for a critical role of FOXO1 activity in CXCR6⁺CD8⁺ T cells of the liver controlling effector function that is required to prevent liver immunopathology.