Soluble Ligands for Activating Natural Killer Receptor (NKG2D) Are Biomarkers for Progression of Hepatic Fibrosis after Liver Transplantation

Abstract

Introduction: Fibrosis progression in liver transplant (LT) patients has a multifactorial origin. Proinflammatory cytokines which can be induced by soluble ligands for activating natural killer receptor (NKG2D) may sustain cell-mediated immune responses, thereby promoting hepatobiliary injury. The role of HLA mismatches and soluble NKG2D ligands (major MHC class I-related chain A and B [sMICA/sMICB] and UL16 binding protein 2 [sULBP2]) in fibrosis progression has not been investigated in the LT setting. Aim: To investigate clinical, laboratory and immunological risk factors for progression of hepatic fibrosis following LT. Methods: A total of 174 LT recipients were enrolled in the study. Patients with recurrent viral disease were excluded. Cytokines were assessed by flow cytometry with the “BD Cytometric Bead Array (CBA) Human Th1/Th2/Th17 Cytokine Kit”. Assessment of sMICA, sMICB and sULBP2 was realized by enzyme linked immunosorbent assay. Screening for anti-HLA class I, class II or MICA antibodies (AB) was performed using Luminex technology. Chi-square or Fischer's exact test was used for comparing categorical data and Student's t-test or Mann-Whitney U test, when appropriate, was used for comparing continuous variables. Multivariate logistic regression analysis was performed to identify independent risk factors for development of cirrhosis after LT. Results: In the univariate analysis, donor age >50 years (p=0.001), presence of anastomosis stenosis (p=0.009), high levels of transaminases (aspartate transaminase (p< 0.0001), alanin aminotransferase (p=0.001)), total bilirubin (p=0.0004) and alkaline phosphatase (p=0.01) were associated with progression to cirrhosis. Immunological risk factors included high serum levels of inflammatory cytokines [Tumor necrosis factor-alpha (TNF)-alpha (p=0.01), interleukin (IL)-10 (p=0.004), IL-6 (p< 0.0001)], presence of donor specific anti-HLA II AB (p=0.01), high serum levels of sMICA (p=0.04), sMICB (p=0.004) and ULPB2 (p< 0.0001). In multivariate analysis, high serum levels of total bilirubin, sMICB and ULPB2 were independent predictors for cirrhosis after LT. Conclusion: sMICB and ULPB2 molecules were associated with cirrhosis in LT patients. Screening of these biomarkers in LT patients may be useful for identifying patients at high risk of hepatic fibrosis progression after LT.