Tissue-resident and innate-like T cells in patients with advanced chronic liver disease

Chronic liver disease results from the orchestrated interplay of components of innate and adaptive immunity in response to liver tissue damage. Recruitment, positioning, and activation of immune cells can contribute to hepatic cell death, inflammation, and fibrogenesis. With disease progression and increasing portal pressure, repeated translocation of bacterial components from the intestinal lumen through the epithelial and vascular barriers leads to persistent mucosal, hepatic, and systemic inflammation which contributes to tissue damage, immune dysfunction, and microbial infection. It is increasingly recognised that innate-like and adaptive T-cell subsets located in the liver, mucosal surfaces, and body cavities play a critical role in the progression of advanced liver disease and inflammatory complications of cirrhosis. Mucosal-associated invariant T cells, natural killer T cells, γδ T cells, and tissue-resident memory T cells in the gut, liver, and ascitic fluid share certain characteristic features, which include that they recognise microbial products, tissue alarmins, cytokines, and stress ligands in tissues, and perform effector functions in chronic liver disease. This review highlights recent advances in the comprehension of human tissue-resident and unconventional T-cell populations and discusses the mechanisms by which they contribute to inflammation, fibrosis, immunosuppression, and antimicrobial surveillance in patients with cirrhosis. Understanding the complex interactions of immune cells in different compartments and their contribution to disease progression will provide further insights for effective diagnostic interventions and novel immunomodulatory strategies in patients with advanced chronic liver disease.

Immunomodulatory receptor VSIG4 is released during spontaneous bacterial peritonitis and predicts short-term mortality

Background & Aims

V-set Ig-domain-containing 4 (VSIG4) is an immunomodulatory macrophage complement receptor modulating innate and adaptive immunity and affecting the resolution of bacterial infections. Given its expression on peritoneal macrophages (PMs), we hypothesised a prognostic role of peritoneal VSIG4 concentrations in patients with spontaneous bacterial peritonitis (SBP).

Methods

We isolated PMs from patients with cirrhosis and analysed VSIG4 expression and release by flow cytometry, quantitative real-time PCR, ELISA, and confocal microscopy. We measured soluble VSIG4 concentrations in ascites from 120 patients with SBP and 40 patients without SBP and investigated the association of soluble VSIG4 in ascites with 90-day survival after SBP using Kaplan–Meier statistics, Cox regression, and competing-risks regression analysis.

Results

VSIG4 expression was high on resting, large PMs, which co-expressed CD206, CD163, and tyrosine-protein kinase Mer (MERTK). VSIG4 gene expression in PMs decreased in patients with SBP and normalised after resolution. During SBP, VSIG4^hi PMs were depleted (25% vs. 57%; p <0.001) and soluble VSIG4 in ascites were higher in patients with SBP than in patients without (0.73 vs. 0.35 μg/ml; p <0.0001). PM activation by Toll-like receptor (TLR) agonists or infection with live bacteria in vitro resulted in a loss of surface VSIG4 and the release of soluble VSIG4. Mechanistically, shedding of VSIG4 from PMs was protease-dependent and susceptible to microtubule transport inhibition. Soluble VSIG4 in ascites exceeded serum concentrations and correlated with serum creatinine, model for end-stage liver disease score and C-reactive protein during SBP. Concentrations of 1.0206 μg/ml or higher indicated increased 90-day mortality (hazard ratio 1.70; 95% CI 1.01–2.86; p = 0.046).

Conclusions

VSIG4 is released from activated PMs into ascites during SBP. Higher peritoneal VSIG4 levels indicate patients with organ failure and poor prognosis.

Lay summary

Patients with liver cirrhosis who develop ascites have an increased risk of infection and mortality. Our study shows that in patients with infected ascites, the complement receptor VSIG4 is released by resident macrophages into the abdominal fluid where it can be measured. Patients with elevated levels of this protein in ascites are at high risk of dying within 90 days.

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VSIG4 expression is high on human resting, large peritoneal macrophages (PMs) that co-express CD206, CD163, and MERTK.

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PM activation by TLR agonists or infection results in the loss of surface VSIG4 and release of soluble VSIG4 (sVSIG4).

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Ascites sVSIG4 correlates with organ dysfunction and inflammation during SBP.

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Higher ascitic fluid sVSIG4 concentrations indicated increased risk of 90-day mortality in 120 patients with SBP.

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Addition of an antibody binding to the extracellular domain of VSIG4 enhanced phagocytosis of bacteria in vitro.

Peritoneal Level of CD206 Associates With Mortality and an Inflammatory Macrophage Phenotype in Patients With Decompensated Cirrhosis and Spontaneous Bacterial Peritonitis

BACKGROUND & AIMS

Peritoneal macrophages (PMs) regulate inflammation and control bacterial infections in patients with decompensated cirrhosis. We aimed to characterize PMs and associate their activation with outcomes of patients with spontaneous bacterial peritonitis (SBP).

METHODS

We isolated PMs from ascites samples of 66 patients with decompensated cirrhosis (19 with SBP) and analyzed them by flow cytometry, quantitative real-time polymerase chain reaction, functional analysis, and RNA microarrays. We used ascites samples of a separate cohort of 111 patients with decompensated cirrhosis (67 with SBP) and quantified the soluble form of the mannose receptor (CD206) and tumor necrosis factor by enzyme-linked immunosorbent assay (test cohort). We performed logistic regression analysis to identify factors associated with 90-day mortality. We validated our findings using data from 71 patients with cirrhosis and SBP. Data from 14 patients undergoing peritoneal dialysis for end-stage renal disease but without cirrhosis were included as controls.

RESULTS

We used surface levels of CD206 to identify subsets of large PMs (LPM) and small PMs (SPM), which differed in granularity and maturation markers, in ascites samples from patients with cirrhosis. LPMs vs SPMs from patients with cirrhosis had different transcriptomes; we identified more than 4000 genes that were differentially regulated in LPMs vs SPMs, including those that regulate the cycle, metabolism, self-renewal, and immune cell signaling. LPMs had an inflammatory phenotype, were less susceptible to tolerance induction, and released more tumor necrosis factor than SPMs. LPMs from patients with cirrhosis produced more inflammatory cytokines than LPMs from controls. Activation of PMs by Toll-like receptor agonists and live bacteria altered levels of CD206 on the surface of LPMs and release of soluble CD206. Analysis of serial ascites fluid from patients with SBP revealed loss of LPMs in the early phase of SBP, but levels increased after treatment. In the test and validation cohorts, patients with SBP and higher concentrations of soluble CD206 in ascites fluid (>0.53 mg/L) were less likely to survive for 90 days than those with lower levels.

CONCLUSIONS

Surface level of CD206 can be used to identify mature, resident, inflammatory PMs in patients with cirrhosis. Soluble CD206 is released from activated LPMs and increased concentrations in patients with cirrhosis and SBP indicate reduced odds of surviving for 90 days.

Mucosal-Associated Invariant T Cells Redistribute to the Peritoneal Cavity During Spontaneous Bacterial Peritonitis and Contribute to Peritoneal Inflammation

BACKGROUND & AIMS

Mucosal-associated invariant T (MAIT) cells are depleted from blood in patients with advanced liver disease and show features of immune dysfunction. Because circulating MAIT cells differ from organ-resident MAIT cells, we aimed to investigate the frequency, phenotype, and function of peritoneal MAIT cells from patients with cirrhosis and spontaneous bacterial peritonitis (SBP).

METHODS

MAIT cells in blood and ascitic fluid from patients with cirrhosis were characterized using flow cytometry. Healthy individuals and noncirrhotic patients undergoing peritoneal dialysis served as controls. MAIT cell migration was studied in transwell assays. Cytokine release in response to infected ascitic fluid and bacterial products was assessed in vitro.

RESULTS

Peritoneal CD3+ CD161hi Vα7.2+ T cells had an inflammatory, tissue retention phenotype, expressing the alpha E integrin, the chemokine receptors CCR5 and CXCR3, and the activation marker CD69 at higher levels than their circulating equivalents. Seventy-seven percent bound to MR1 tetramers loaded with the pyrimidine intermediate 5-(2-oxopropylideneamino)-6-d-ribitylaminouracil. The ratio of peritoneal to blood MAIT cell frequency increased from 1.3 in the absence of SBP to 2.6 at diagnosis and decreased by day 3. MAIT cells migrated toward infected ascitic fluid containing CCL5 and CCL20 and released cytokines in an MR1-restricted fashion. Whereas the depleted circulating MAIT cell pool displayed features of immune exhaustion, peritoneal MAIT cells remained competent producers of inflammatory cytokines in response to bacterial products. Peritoneal MAIT activation correlated with systemic inflammation, suggesting a possible link between peritoneal and systemic immunity.

CONCLUSIONS

Peritoneal MAIT cells phenotypically and functionally differ from circulating MAIT cells in decompensated cirrhosis and redistribute to the peritoneum during SBP.