Biliary obstruction results in PD-1-dependent liver T cell dysfunction and acute inflammation mediated by Th17 cells and neutrophils

Biliary obstruction is a common clinical problem that is associated with intrahepatic inflammation and impaired immunity. PD-1 is well known to mediate T cell dysfunction but has been reported to promote and attenuate acute inflammation in various injury models. With the use of a well-established murine model of BDL, we studied the effects of intrahepatic PD-1 expression on LTC function, inflammation, and cholestasis. Following BDL, PD-1 expression increased significantly among LTCs. Increased PD-1 expression following BDL was associated with decreased LTC proliferation and less IFN-gamma production. Elimination of PD-1 expression resulted in significantly improved proliferative capacity among LTC following BDL, in addition to a more immunostimulatory cytokine profile. Not only was LTC function rescued in PD-1(-/-) mice, but also, the degrees of biliary cell injury, cholestasis, and inflammation were diminished significantly compared with WT animals following BDL. PD-1-mediated acute inflammation following BDL was associated with expansions of intrahepatic neutrophil and Th17 cell populations, with the latter dependent on IL-6. PD-1 blockade represents an attractive strategy for reversing intrahepatic immunosuppression while limiting inflammatory liver damage.