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

Johanna Reißing; Philipp Lutz; Mick Frissen; Oluwatomi Ibidapo-Obe; Philipp A Reuken; Theresa H Wirtz; Sven Stengel; Stefanie Quickert; Michael Rooney; Karsten Große; Henning W Zimmermann; Christian Trautwein; Andreas Stallmach; Tony Bruns

doi:10.1016/j.jhepr.2021.100391

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

JHEP Rep. 2021 Nov 3;4(1):100391. doi: 10.1016/j.jhepr.2021.100391. eCollection 2022 Jan.

Authors

Affiliations

¹ Department of Internal Medicine III, University Hospital RWTH Aachen, Aachen, Germany.
² Department of Internal Medicine I, University of Bonn, Bonn, Germany.
³ German Center for Infection Research, University of Bonn, Bonn, Germany.
⁴ Department of Internal Medicine IV (Gastroenterology, Hepatology, and Infectious Diseases), Jena University Hospital, Jena, Germany.

Abstract

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.

Keywords: AF, ascitic fluid; BSA, bovine serum albumin; Bacterial infection; Biomarker; C3, complement component 3; CCR2, C-C chemokine receptor type 2; EEA1, early endosome antigen 1; FCS, foetal calf serum; FMO, fluorescence minus one; HLA-DR, human leucocyte antigen-DR isotype; IMC, isotype-matched control; INR, international normalised ratio; LAMP2, lysosome-associated membrane protein 2; LPS, lipopolysaccharide; MACS, magnet-activated cell sorting; MELD, model for end-stage liver disease; MERTK, tyrosine-protein kinase Mer; MFI, median fluorescence intensity; MMP, matrix metalloproteinase; MOI, multiplicity of infection; MPLA, monophosphoryl lipid A; PAMP, pathogen-associated molecular pattern; PD-L1, programmed cell death 1 ligand 1; PFA, paraformaldehyde; PM, peritoneal macrophage; Prognostic factor; Risk of death; SBP, spontaneous bacterial peritonitis; TAPI-2, tumour necrosis factor protease inhibitor 2; TLR, Toll-like receptor; TNF, tumour necrosis factor; VSIG4, V-set Ig-domain-containing 4; qRT-PCR, quantitative real-time PCR; sVSIG4, soluble V-set Ig-domain-containing 4.