Anti-infective mucosa-associate invariant T cell - cholangiocyte interaction in tissue repair.

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that are involved in both protective and detrimental processes in various diseases due to their broad range of effector functions. While initially characterized by their anti-microbial activity, more recent findings show that TCR-dependent activated MAIT cells contribute to tissue repair and support anti-viral programs in antigen-presenting cells (APC). MAIT cells are highly enriched in mucosal tissues such as the liver and intestine and have been described with tissue-specific markers. Despite their abundance near intrahepatic bile ducts and their presence in extrahepatic bile ducts of patients with primary sclerosing cholangitis (PSC) – a disease marked by inflammation and fibrosis – their specific interaction with cholangiocytes remains poorly understood. This thesis investigates the interaction between human MAIT cells and cholangiocyte cell lines, focusing on tissue repair by anti-infective MAIT cells, based on the characteristics of PSC. First, the early adaptation of MAIT cells to intact intra- or extrahepatic cholangiocytes was analyzed by proteome profiling after 24 hours of co-culture. The data exhibited cholangiocyte-specific adaptation characterized by the upregulation of cell adhesion molecules. In addition, proteins associated with epithelial cell differentiation were upregulated, suggesting that MAIT cells exert their tissue repair function in the presence of cholangiocytes. Based on this, a scratch assay was used to show for the first time that both unstimulated and TCR-activated MAIT cells support tissue repair, with MAIT cells being recruited to the injury site early during the repair process. This expands their previously described bystander role in later repair phases. To identify potential recruitment factors, the secretome of injured cholangiocytes was analyzed, revealing 143 secreted proteins in response to the damage. Among them, IL6 – known for its early involvement in wound healing – was identified as a key factor mediating MAIT cell recruitment and function, as blocking of IL6 abolished the tissue repair effect of MAIT cells. In contrast, CXCL16, previously described as a recruitment factor for murine MAIT cells in skin wounds, had no effect on human MAIT cell recruitment, effector phenotype, or tissue repair function. Finally, the recently discovered support of anti-viral programs in APCs by TCR-activated MAIT cells was also demonstrated in cholangiocytes. Furthermore, the combination of the infection and tissue repair assay showed that both unstimulated and activated MAIT cells support tissue repair in cholangiocytes during viral infection. However, only TCR-activated MAIT cells were able to reduce the viral load in infected cholangiocytes, although they did not enhance the intrinsic anti-viral response of the injured cholangiocytes themselves. In summary, this thesis demonstrates that MAIT cells undergo cholangiocyte-specific adaptation and contribute to tissue repair in both unstimulated and activated states, which is IL6-dependent, as is their recruitment. Furthermore, MAIT cells exhibit anti-viral activity upon activation without enhancing anti-viral pathways of injured cholangiocytes.