Introduction: Liver fibrosis is the hallmark characteristic of the progression to liver chronic rejection (CR), an irreversible, progressive disease that leads to graft loss, requiring re-transplantation. Emerging evidence from our laboratory and other groups has suggested that IL-33 and its primary functional receptor suppression of tumorigenicity 2 (ST2) are involved in the pathogenesis of hepatic fibrosis. Considering that, our aim was to study the role of IL-33/ST2 axis in the fibrogenic mechanism involved in the CR after liver transplant (LT) in humans.
Materials and Methods: The study included liver biopsies and tissue samples from LT patients [Non-rejection (NR)=9, patients with chronic rejection [CR=4] and control samples from donor allograft [Control=9]. Liver fibrosis stage was determined by Masson’s trichrome staining. The frequency and distribution of immune cell populations were evaluated by immunohistochemistry. Histological analyses of collagen deposition were performed by Sirius Red staining. Gene expressions were evaluated by quantitative real-time PCR. Analysis of immunological parameters, clinical laboratory and METAVIR score were made using the Kruskal–Wallis with Dunn’s post-test. Correlations were evaluated with the Spearman rank correlation test, p<0.05 was considered statistically significant. The protocol was approved by the Institutional Review Board of HUFF (DDI [1490] 2419).
Results: LT patients with CR rejection had significantly higher intrahepatic CD3+ and CD4+ cell frequency at the periportal area than NR patients (p<0.05). This cell increment showed significant correlation with advanced fibrosis, collagen deposition and altered levels of functional liver markers as AST, ALT, and ALP (p<0.05). Interestingly, CD8 cell frequency was similar in CR and NR groups (p>0.05), independently of the area analysed. Hepatic levels of IL-33 and ST2 total were increased during CR compared with the control group, while ST2s, a soluble form of the receptor which acts as decoy factor was not different among groups. ST2 levels correlated positively with altered levels of functional liver markers as TB, AST, ALT, and ALP (p<0.05), suggesting that ST2 expression is induced by hepatocellular and cholestatic damage. Fibrotic genes expression, such as α-SMA and TGF-ß, showed an increment in the CR group compared with controls and the NR group (p>0.05). Moreover, α-SMA expression positively correlated with METAVIR score in LT patients (p<0.05).
Conclusions: These findings suggest that IL-33/ST2 axis is modulated during CR after liver transplant and blocking the signalling of this axis may be a new therapeutic approach to reduce the development of fibrosis of CR patients.