Single cell RNA sequencing reveals regional heterogeneity of hepatobiliary innate lymphoid cells in a tissue-enriched fashion.

IL-33 promotes type 2 immunity, epithelial repair, and tissue fibrosis by activating group 2 innate lymphoid cells (ILC2). ILC2 lack all known surface markers of mature T, B, NK, and myeloid cell lineages (Linneg), express the IL-33 receptor ST2, and release type 2 cytokines which contribute to cholangiocyte proliferation and activation of hepatic stellate cells. This pathway results in massive proliferation of the extrahepatic bile duct (EHBD) but also exacerbates liver fibrosis, suggesting that there may be tissue-specific subpopulations of IL-33-induced ILC. To determine the tissue-specific subsets of ILC in the hepatobiliary system, we analyzed CD45+Linneg mononuclear cells from IL-33 treated adult Balb/c mouse liver or EHBD by single cell RNA sequencing. Principal component analysis identified 6 major CD45+Linneg cell classes, two of which were restricted to the EHBD. One of these classes, biliary immature myeloid (BIM) cells, was predicted to interact with ILC2 by a network of shared receptor-ligand pairs. BIM highly expressed Gp49 and ST2 receptors on the cell surface while lacking surface expression of markers for mature myeloid cells. In conclusion, single cell RNA sequencing identified IL-33 responsive cell groups regionally confined to the liver or extrahepatic bile duct, including a novel population of CD45+Linneg Gp49-expressing mononuclear cells.