Expansion of innate CD5pos B cells expressing high levels of CD81 in hepatitis C virus infected liver

Background/Aims: Association of hepatitis C virus (HCV) with increased autoantibodies, mixed cryoglobulinaemia, non-Hodgkinʹs B-cell lymphoma and increased peripheral innate (CD5pos) B cells suggests a role for B-lymphocytes in the pathogenesis of HCV-infection. Methods: Flow cytometry was used to estimate CD5pos B cell levels and CD81 co-expression in chronic HCV infection. Viral load was assessed using PCR. Results: We demonstrate expansion of innate B cells in HCV-infected liver from patients with fibrosis score less than stage II (39%, % of total B cells, P=0.002) and end stage HCV cirrhosis (20%, P<0.05) compared with normal liver (8%). Expression of CD81, a signal transducing molecule and putative HCV receptor, was significantly increased on peripheral blood CD5pos B cells compared with conventional B cells (P=0.0001). Higher levels of CD81 on CD5pos B cells were more dramatic in the liver of HCV-infected individuals. However, no significant difference was observed in the viral load of CD5posCD81High B cells and CD5negCD81Low B cells. Conclusions: Increased expression of CD81 on innate B cells, a population that is expanded in the livers and peripheral blood of chronic HCV-infected patients, suggests a role in viral specific activation and clonal proliferation in chronic HCV infection.