The liver controls regulatory T cell populations by enclysis, a CD4+ T cell engulfment process

Abstract

Abstract Background and Aims Regulatory T cells (Treg) dampen inflammation and they are increased in the liver compared to blood, contributing to a tolerising environment. The swift neutralisation of Treg cells is important to enable immune effector functions to combat infection, but the mode of this is not understood. We noted that hepatocytes preferentially engulfed live Treg cells, and we set out to characterise the mechanism and outcome of this new phenomenon we termed “enclysis”. Method We measured enclysis, the enclosure and lysis of Treg cells, in vitro and ex vivo using perfused liver wedges, in the presence of inhibitors of known cell-in-cell processes. Reporter dyes for viability, mitochondrial activity and acidification were used to determine enclysis outcome. Cell-in-cell structures were documented by light, confocal, electron and multiphoton microscopy. FoxP3+ Treg and T-bet+ T helper cells were enumerated in donor and in end-stage disease livers of autoimmune and viral diseases. Results Hepatocytes preferentially engulfed live Treg cells in a process that differed in mechanism and kinetic to previously described cell-in-cell structures (efferocytosis, suicidal emperipolesis, entosis). Enclysis reflects the enclosure and specific lysis of live Treg cells inside hepatocytes, and beta-catenin-positive enclytic vesicles were connected to the endocytic pathway. Enclysis was increased in patients with autoimmune compared to viral hepatitis (p=0.0011), offering an explanation for the breach of tolerance in the liver. Conclusion Enclysis is the preferential engulfment and deletion of live Treg cells by hepatocytes and can be modulated pharmacologically, offering a new therapeutic target for liver immune regulation.