Chronic Hepatitis C Virus Infection Breaks Tolerance and Drives Polyclonal Expansion of Autoreactive B Cells

Abstract

b Chronic Hepatitis C virus (HCV) infection has been linked with B cell lymphoproliferative disorders and several autoimmune-related diseases. The mechanisms of how chronic viral infection affects B cell development and predisposes the patients to autoimmune manifestations are poorly understood. In this study, we established an experimental system to probe the B cell responses and characterize the antibodies from chronic-HCV-infected individuals. We identified an unusual polyclonal expansion of the IgM memory B cell subset in some patients. This B cell subset is known to be tightly regulated, and autoreactive cells are eliminated by tolerance mechanisms. Genetic analysis of the immunoglobulin (Ig) heavy chain variable gene (V H ) sequences of the expanded cell population showed that the levels of somatic hypermutation (SHM) correlate with the extent of cell expansion in the patients and that the V H genes exhibit signs of antigen-mediated selection. Functional analysis of the cloned B cell receptors demonstrated autoreactivity in some of the expanded IgM memory B cells in the patients which is not found in healthy donors. In summary, this study demonstrated that, in some patients, chronic HCV infection disrupts the tolerance mechanism that normally deletes autoreactive B cells, therefore increasing the risk of developing autoimmune antibodies. Long-term follow-up of this expanded B cell subset within the infected individuals will help determine whether these cells are predictors of more-serious clinical manifestations. Hepatitis C virus (HCV) is a single-stranded RNA virus that is transmitted predominantly through direct blood contact, such as accidental needle sticks in the health care workplace, blood transfusions, and needle sharing among intravenous drug users (reviewed in reference 33). About 70% of those infected cannot clear the virus and succumb to persistent infection (reviewed in reference 22). Of those, more than half will develop some form of liver disease and ϳ2 to 3% will develop liver cancer over a course of 20 to 40 years (4, 17). HCV has also been associated with B cell and antibody abnormalities (non-Hodgkin's lymphoma [NHL] [40]) and a number of autoimmune diseases (mixed cryoglobulinemia [MC] [2], celiac disease [56], Sjögren's syndrome [68], and systemic autoimmune diseases [53]). The contribution of the virus to these diseases is unclear. One hypothesis is that E2, a glycoprotein found on the surface of HCV, binds to CD81 instead of B cell receptors (BCRs) on B cells, stimulating cell proliferation (55) and hypermutation of immunoglobulin (Ig) genes (38). Prolonged stimulation by E2 during chronic infection can eventually lead to some form of B cell lymphoproliferative disorder. It is also thought that HCV itself may provide a chronic antigen stimulus that drives clonal expansion of B cells. In support of this, it was shown that Ig cloned from NHL biopsy specimens bound E2 (50). In addition, Charles et al. demonstrated an antigen-driven expansion of peripheral blood (PB) IgM ϩ CD27 ϩ B c...

Abnormal phenotypic features of IgM+B cell subsets in patients with chronic hepatitis C virus infection

“…Consistent with a previous report (17), the present study demonstrated that an increase in CD27+IgM+B cells was associated with HCV infection. The frequency of CD27-IgM+B cells in patients with CHC was similar to that in HCs.…”

“…Roughan et al (17) demonstrated that IgM+ memory B cells were expanded in patients with CHC, and identified that the unusual polyclonal expansion of the IgM+ memory B cell subset was made up of autoreactive B cells. Consistent with a previous report (17), the present study demonstrated that an increase in CD27+IgM+B cells was associated with HCV infection.…”

“…Based on expression of CD5, B cells were divided into CD5+B cells (B1 cells) and CD5-B cells (B2 cells) (20). Depending on the expression of CD27, a distinct memory B cell marker, IgM+B cells were divided into naive subsets (CD27-IgM+B cells) and memory subsets (CD27+IgM+B cells) (17). In addition, CD21 was used to identify activated subsets (CD21-cells) and resting subsets (CD21+cells) in naïve B cells and memory B cells (7).…”

“…Immunoglobulin (Ig) M+B cells are responsible for the production of IgM antibodies and are involved in the pathogenesis of viral infections and autoimmunity diseases (14)(15)(16). Roughan et al (17) determined that there is a higher frequency of circulating IgM+B memory subsets in the peripheral blood of patients with CHC; however the phenotypic features of different IgM+B cell subsets and associated risk factors in patients with CHC remain unknown.…”

Autoimmunity and infection in Sjögren's syndrome

“…Some of these B-cells in HCV-infected patients are autoreactive [68]; and, therefore, may predispose to SS.…”