Characterization and role of intra-hepatic regulatory T cells in chronic hepatitis C pathogenesis

Background & Aims In chronic hepatitis C (CHC), HCV-specific T-cell responses are often dysfunctionnal. In vitro data point out that regulatory T cells (Treg) are able to suppress HCV-specific lymphocyte proliferation and cytokine secretion but their implication in this pathology is still debated. Methods Three complementary approaches were performed to investigate phenotype, frequency or localization of intra-hepatic Treg in treatment naïve CHC patients. Double immunohistochemical analysis was performed in 20 formalin-fixed biopsies with CD8/FoxP3 and CD4/FoxP3 antibodies. Cellular markers and cytokines were investigated by quantitative RT-PCR in 27 additional frozen biopsies. Eight other fresh liver biopsies were selected for complementary analysis of immunophenotyping and frequency of intra-hepatic Treg. Results Immunohistochemical analyses showed the presence of intra-hepatic CD4+ FoxP3+ T cells while CD8+ FoxP3+ T cells were very scarce. CD4+ FoxP3+ T cells were located in necro-inflammatory areas in contact with CD8+ T cells, suggesting that Treg-mediated inhibition of CD8+ T cell proliferation may occur by cell–cell contact. RT-PCR analyses showed strong correlations between CD8, FoxP3, and IL-10 with emergence of four distinct gene clusters, CD8-FoxP3, CD8-IL-10, TGF-β−IL-10, and TNF-α-TGF-β. No correlation was found between serum viral load and any immune markers. Interestingly, the FoxP3+ /CD8+ cells ratio significantly decreased in severe fibrosis ( F >3) due to the dramatic decline of FoxP3 cells. Conclusions This study provides new insights into the histological localization of Treg within HCV-infected liver, with a special accumulation of CD4+ FoxP3+ Treg cells in necro-inflammatory areas, in contact with CD8+ T cells. Our results suggest a link between Treg, CD8, and IL-10 which altogether could balance immune responses against the virus to avoid immunopathogenesis.