Activation of naïve B lymphocytes via CD81, a pathogenetic mechanism for hepatitis C virus-associated B lymphocyte disorders

Abstract

Infection with hepatitis C virus (HCV), a leading cause of chronic liver diseases, can associate with B lymphocyte proliferative disorders, such as mixed cryoglobulinemia and non-Hodgkin lymphoma. The major envelope protein of HCV (HCV-E2) binds, with high affinity CD81, a tetraspanin expressed on several cell types. Here, we show that engagement of CD81 on human B cells by a combination of HCV-E2 and an anti-CD81 mAb triggers the JNK pathway and leads to the preferential proliferation of the naïve (CD27 ؊ ) B cell subset. In parallel, we have found that B lymphocytes from the great majority of chronic hepatitis C patients are activated and that naïve cells display a higher level of activation markers than memory (CD27 ؉ ) B lymphocytes. Moreover, eradication of HCV infection by IFN therapy is associated with normalization of the activation-markers expression. We propose that CD81-mediated activation of B cells in vitro recapitulates the effects of HCV binding to B cell CD81 in vivo and that polyclonal proliferation of naïve B lymphocytes is a key initiating factor for the development of the HCV-associated B lymphocyte disorders.monoclonal antibody ͉ multimeric engagement ͉ B cell antigen receptor ͉ cryoglobulinemia H epatitis C virus (HCV) is a positive-stranded RNA virus of the Flaviviridae family (1). The HCV genome is 9.6 kb in length, with one large translational ORF encoding a single polyprotein, which is processed by host and viral proteases into at least three structural and seven nonstructural proteins with various enzymatic activities (1). Two heavily N-glycosylated proteins E1 and E2 are virion-envelope proteins and form heterodimers in vitro (2). An estimated 170 million individuals are infected with HCV worldwide (3). HCV infection is associated with the development of chronic hepatitis, cirrhosis, and hepatocellular carcinoma (4). B cell abnormalities, including cryoglobulinemia (5) and an increased risk of B cell non-Hodgkin lymphoma (6, 7), have been reported in a minority of HCV infections.Until very recently, it was not possible to grow HCV in cell culture, therefore studies of virus interaction with human cells have been surrogated by the assessment of binding and entry of HCV recombinant glycoproteins (8) or virus pseudotypes (9).We have previously reported that HCV-E2 protein binds with high affinity to the large extracellular loop of human CD81 (CD81-LEL) and that ''bona fide'' HCV particles bind human CD81 (10). Recently, it has been demonstrated that CD81 is required for entry and infection of human cells by in vitro-generated infectious HCV (11). CD81 is a widely distributed cell-surface tetraspanin that participates in different molecular complexes on various cell types, including B, T, and natural killer (NK) cells (12). On human B cells, CD81 is known to form a costimulatory complex with CD19 and CD21 (13,14) and that coligation of the B cell antigen receptor (BCR) with any of the components of this costimulatory complex lowers the threshold required for BCR-mediated B cell proliferat...

Antigenic cooperation among intrahost HCV variants organized into a complex network of cross-immunoreactivity

“…This threshold was estimated to be up to 30 Ab molecules per virion for West Nile virus (53,54) and is represented in our model with the relation u i,j = v K j,i between the probabilities u i,j and v j,i of neutralization and immune stimulation. The neutralization effectiveness of the Ab may be further hampered by dilution with low-affinity Abs resulting from boosting of different memory B cells by a viral variant or from polyclonal antigen-independent activation of naive B cells by HCV (55).…”

Expansion of Functionally Anergic CD21−/low Marginal Zone-like B Cell Clones in Hepatitis C Virus Infection-Related Autoimmunity

“…Consistent with this idea, Ig cloned from a HCV patient with B-NHL was shown to bind to the HCV structural protein E2 (14). It also has been suggested that HCV-E2 directly activates polyclonal B cells by binding to CD81 (15). Others have proposed that direct HCV infection of B cells may cause oncogenic transformation, particularly through t(14;18) translocation (16,17).…”

Preterm neonates show marked leukopenia and lymphopenia that are associated with increased regulatory T-cell values and diminished IL-7

“…Mouse antihuman antibodies were used to identify immune populations as described in the literature (39,40):anti-hCD45-FITC, anti-hCD4-ECD, antihCD45RA-ECD, anti-hCD127-PE, anti-hCD25-PECy5, anti-hCD3-PECy7, anti-hCD27-PECy5, anti-hCD8-PECy7, anti-hCD31-FITC, anti-hCD19-ECD, anti-hCD16-PECy5, anti-hCD56-PE, and corresponding isotype controls (all from Beckman Coulter). Absolute number of immune subtypes was determined using Flow-Count Fluorospheres and Flow-Count method (Beckman Coulter).…”