Role of MAIT cells in primary biliary cholangitis. - PROJECT SUMMARY Primary biliary cholangitis (PBC; previously called primary biliary cirrhosis) is an autoimmune liver disease characterized by immune-mediated destruction of biliary epithelial cells (BEC), resulting in biliary obstruction, and progressive liver fibrosis culminating in end-stage liver cirrhosis. PBC is more frequent in females (10:1 ratio), and is one of the most common autoimmune liver diseases. Approved treatments for PBC, however, are not highly effective. Hence, there is a significant need to identify therapeutic targets. We propose to do this by analyzing the underlying immune and genetic pathogenic mechanisms by focusing on the role of mucosal associated invariant T (MAIT) cells. MAIT cells express an invariant TCRa chain and recognize antigens presented by MR1, a nonpolymorphic MHC class I-like molecule. MAIT cells have the same specificity in everyone, and our focus also is motivated by their high prevalence in human liver in vasculature surrounding biliary ducts; BECs express MR1 and can present antigens to MAIT cells; and MAIT cells respond to products including both microbial riboflavin metabolites and also a sulfated bile acid. Furthermore, in some studies MAIT cells were reported increased in liver of PBC patients, but this is controversial, and there are limitations to the prior studies. Additionally, the PIs have novel insights into the genetics of PBC pathogenesis from the Database of Immune Cell Expression, eQTLs, Epigenomics (DICE) project, established to define genes and immune cell types linked to disease risk. Using DICE samples, we conducted eQTL studies in MAIT cells and highlighted the impact of several previously identified PBC-risk variants on the expression of ‘candidate genes’ especially in MAIT cells. Thus, our genetic analysis (preliminary data) provides direct evidence that some PBC-risk variants are likely to modulate the function of MAIT cells to influence disease pathogenesis. Here we propose a thorough characterization of MAIT cells in PBC patients and controls, including those with early-stage disease, and late- stage patients. The methods will include multiplex immunohistochemistry, sc-RNA-seq to reveal MAIT cell heterogeneity and functions, as well as spatial transcriptomics to identify interacting cell types. Using RNAi silencing as well as over expression, we will determine the effect on human MAIT cells of altering the expression of PBC risk genes that DICE data show are eQTLs in MAIT cells. To gain insight into mechanisms, we will explore two mouse models of PBC, methods to greatly increase long-term the number of MAIT cells in the liver, so the mice will be more human-like for this parameter, including a strain with 10-fold higher frequency of MAIT cells. The experimental design will allow us to evaluate the effects of the absence of MAIT cells or their increase, and the result of modulation of expression of PBC risk genes relevant for human MAIT cell function in vivo. Overall, the studies will establish the importance of MAIT cells in PBC and will identify genes that could indicate attractive novel targets for modulating the function of these cells to achieve better clinical outcomes.
