CD8+ T cells actively penetrate hepatocytes via the CD44/p‐ERM/F‐actin pathway in autoimmune hepatitis

Objective Emperipolesis is a pathological feature for the diagnosis of autoimmune hepatitis (AIH). We have previously found that CD8+ T cells participated in the emperipolesis in AIH. In this study we aimed to clarify the characteristics and molecular mechanisms of emperipolesis in patients with AIH in vitro and in mice with α‐Galactosylceramide (α‐GalCer)‐induced acute hepatitis. Methods The peripheral blood mononuclear cells (PBMC) of patients with various chronic liver diseases and healthy controls were co‐cultured with hepatic cell lines to induce emperipolesis in vitro. Confocal staining was performed to illustrate the cellular types and potential mechanisms of emperipolesis in AIH. In addition, a murine model of α‐GalCer‐induced acute hepatitis that mimics human AIH was used to confirm the role of CD44/p‐ERM/F‐actin in the emperipolesis process in vivo. Results In the co‐cultured system of PBMC and hepatic cell line, emperipolesis was observed most commonly in patients with AIH. The main cells participating in emperipolesis were CD8+ T cells, and they penetrated hepatic cells actively via the CD44/p‐ERM/F‐actin pathway. As a result, most CD8+ T cells engulfed by hepatic cells underwent apoptosis. In the α‐GalCer‐induced acute hepatitis model, emperipolesis was observed around the inflammatory foci and was inhibited by the ezrin phosphorylation inhibitor NSC668394. Similarly, activated murine CD8+ T cells penetrated primary hepatocytes via the CD44/p‐ERM/F‐actin pathway in vitro. Conclusions CD8+ T cells penetrate hepatic cells actively via the CD44/p‐ERM/F‐actin signaling pathway and undergo apoptosis. This may be a compensatory mechanism to attenuate the overwhelming immune attack in AIH. Autoimmune hepatitis (AIH) is an inflammatory liver disorder related to an aberrant autoimmune reaction to hepatocytes. Emperipolesis is one of the typical histological features for diagnosing AIH. We have previously found that CD8+ T cells were involved in emperipolesis in biopsied AIH tissues. In this study we demonstrated that CD8+ T cells penetrated hepatocytes actively via the CD44/p‐ERM/F‐actin signaling pathway and underwent apoptosis after co‐cultured with the peripheral blood mononuclear cells of the patients with AIH and the hepatic cell line in vitro, as well as in a murine model of α‐Galactosylceramide‐induced acute hepatitis. This may illustrate a feedback mechanism to maintain tolerance to autoantigen in the liver. However, in AIH abundant self‐reacti