Mucosa-associated invariant T cells link intestinal immunity with antibacterial immune defects in alcoholic liver disease.

BACKGROUND/AIMS: Intestinal permeability with systemic distribution of bacterial products are central in the immunopathogenesis of alcoholic liver disease (ALD), yet links with intestinal immunity remain elusive. Mucosa-associated invariant T cells (MAIT) are found in liver, blood and intestinal mucosa and are a key component of antibacterial host defences. Their role in ALD is unknown. METHODS/DESIGN: We analysed frequency, phenotype, transcriptional regulation and function of blood MAIT cells in severe alcoholic hepatitis (SAH), alcohol-related cirrhosis (ARC) and healthy controls (HC). We also examined direct impact of ethanol, bacterial products from faecal extracts and antigenic hyperstimulation on MAIT cell functionality. Presence of MAIT cells in colon and liver was assessed by quantitative PCR and immunohistochemistry/gene expression respectively. RESULTS: In ARC and SAH, blood MAIT cells were dramatically depleted, hyperactivated and displayed defective antibacterial cytokine/cytotoxic responses. These correlated with suppression of lineage-specific transcription factors and hyperexpression of homing receptors in the liver with intrahepatic preservation of MAIT cells in ALD. These alterations were stronger in SAH, where surrogate markers of bacterial infection and microbial translocation were higher than ARC. Ethanol exposure in vitro, in vivo alcohol withdrawal and treatment with Escherichia coli had no effect on MAIT cell frequencies, whereas exposure to faecal bacteria/antigens induced functional impairments comparable with blood MAIT cells from ALD and significant MAIT cell depletion, which was not observed in other T cell compartments. CONCLUSIONS: In ALD, the antibacterial potency of MAIT cells is compromised as a consequence of contact with microbial products and microbiota, suggesting that the 'leaky' gut observed in ALD drives MAIT cell dysfunction and susceptibility to infection in these patients.

Blockade of PD1 and TIM3 restores innate and adaptive immunity in patients with acute alcoholic hepatitis.

BACKGROUND & AIMS: Susceptibility to bacterial infection is a feature of alcohol-related liver disease. Programmed cell death 1 (PD1), the T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3, also known as hepatitis A virus cellular receptor 2), and their respective ligands-CD274 (also known as PD ligand 1 [PDL1]) and galectin-9-are inhibitory receptors that regulate the balance between protective immunity and host immune-mediated damage. However, their sustained hyperexpression promotes immune exhaustion and paralysis. We investigated the role of these immune inhibitory receptors in driving immune impairments in patients with alcoholic liver disease. METHODS: In a prospective study, we collected blood samples from 20 patients with acute alcoholic hepatitis (AAH), 16 patients with stable advanced alcohol-related cirrhosis, and 12 healthy individuals (controls). Whole blood or peripheral blood mononuclear cells were assessed for expression of PD1, PDL1, TIM3, galectin-9, and Toll-like receptors on subsets of innate and adaptive immune effector cells. We measured antibacterial immune responses to lipopolysaccharide (endotoxin) using ELISpot assays, and used flow cytometry to quantify cytokine production, phagocytosis, and oxidative burst in the presence or absence of blocking antibodies against PD1 or TIM3. RESULTS: Antibacterial innate and adaptive immune responses were greatly reduced in patients with AAH, compared with controls, and patients with alcohol-related cirrhosis had less severe dysfunctions in innate immune effector cells and preserved functional T-cell responses. Fewer T cells from patients with AAH produced interferon gamma in response to lipopolysaccharide, compared with controls. In addition, patients with AAH had greater numbers of interleukin 10-producing T cells, and reduced levels of neutrophil phagocytosis and oxidative burst in response to Escherichia coli stimulation, compared with controls. T cells from patients with AAH, but not alcohol-related cirrhosis, expressed higher levels of PD1 and PDL1, or TIM3 and galectin-9, than T cells from controls. Antibodies against PD1 and TIM3 restored T-cell production of interferon gamma, reduced the numbers of interleukin 10-producing T cells, and increased neutrophil antimicrobial activities. Circulating levels of endotoxin in plasma from patients with AAH caused over expression of immune inhibitory receptors on T cells via Toll-like receptor 4 binding to CD14(+) monocytes. CONCLUSIONS: Antibacterial immune responses are impaired in patients with AAH. Lymphocytes from these patients express high levels of immune inhibitory receptors, produce lower levels of interferon gamma, and have increased IL10 production due to chronic endotoxin exposure. These effects can be reversed by blocking PD1 and TIM3, which increase the antimicrobial activities of T cells and neutrophils.