Plasticity between type 2 innate lymphoid cell subsets and amphiregulin expression regulates epithelial repair in biliary atresia

Background and aims: Although a dysregulated type 1 immune response is integral to the pathogenesis of biliary atresia, studies in both humans and mice have uncovered a type 2 response, primarily driven by type 2 innate lymphoid cells. In nonhepatic tissues, natural type 2 innate lymphoid cell (nILC2s) regulate epithelial proliferation and tissue repair, whereas inflammatory ILC2s (iIlC2s) drive tissue inflammation and injury. The aim of this study is to determine the mechanisms used by type 2 innate lymphoid cell (ILC2) subpopulations to regulate biliary epithelial response to an injury.

Approach and results: Using Spearman correlation analysis, nILC2 transcripts, but not those of iILC2s, are positively associated with cholangiocyte abundance in biliary atresia patients at the time of diagnosis. nILC2s are identified in the mouse liver through flow cytometry. They undergo expansion and increase amphiregulin production after IL-33 administration. This drives epithelial proliferation dependent on the IL-13/IL-4Rα/STAT6 pathway as determined by decreased nILC2s and reduced epithelial proliferation in knockout strains. The addition of IL-2 promotes inter-lineage plasticity towards a nILC2 phenotype. In experimental biliary atresia induced by rotavirus, this pathway promotes epithelial repair and tissue regeneration. The genetic loss or molecular inhibition of any part of this circuit switches nILC2s to inflammatory type 2 innate lymphoid cell-like, resulting in decreased amphiregulin production, decreased epithelial proliferation, and the full phenotype of experimental biliary atresia.

Conclusions: These findings identify a key function of the IL-13/IL-4Rα/STAT6 pathway in ILC2 plasticity and an alternate circuit driven by IL-2 to promote nILC2 stability and amphiregulin expression. This pathway induces epithelial homeostasis and repair in experimental biliary atresia.