Analysis of B-lymphocyte differentiation in patients infected with hepatitis C virus

To clarify whether some of the functions of B lymphocytes could be affected during hepatitis C virus (HCV) infection, phenotypic characteristics of B lymphocytes from HCV-infected patients and their capacity to differentiate into immunoglobulins (Ig)-secreting cells were studied. B lymphocytes differentiation was investigated for patients untreated and non-responders (n=9), treated and non-responders (n=6), responders (n=6), long-term responders (n=9) to therapy and seronegative controls (n=14) following in vitro stimulation with S. aureus strain Cowan I mitogen. HCV sequences in purified B lymphocytes were detected by RT-PCR. It was found that HCV-patients harbor a similar mean percentage of B cells and a normal level of naïve B cells (% IgM+/IgD+ cells=79.7 +/- 15.4 for untreated non-responders, 57.1 +/- 22.9 for treated non-responders, 44.3 +/- 29.1 for responders, 75.7 +/- 16 for long-term responders) as compared with controls. It was also found that peripheral blood mononuclear cells (PBMCs) of patients or controls produced similar amounts of IgG, A, and M in vitro. A total of 57% of untreated non-responders versus 17% of treated non-responders were able to produce HCV-specific antibodies. Interestingly, B lymphocytes from PBMCs able to secrete anti-HCV antibodies contained HCV positive strand RNA, although no systematic detection of the negative strand was found. These data suggest that signaling through the B cell receptor (BCR) in B lymphocytes of HCV-infected patients appears normal whatever their response to therapy. The capacity to secrete HCV-specific IgG seemed to be linked to the presence of positive strand RNA rather than virus replication.