Hepatitis C virus-associated B-cell proliferation--the role of serum B lymphocyte stimulator (BLyS/BAFF)

B lymphocyte stimulator (BLyS) is known to support B-cell proliferation (BCP) in B-cell haemopathies and autoimmune diseases. We assume that BLyS may play a role in the initiation and expression of hepatitis C virus (HCV)-associated BCP. We assessed BLyS serum levels in HCV-infected patients and in various forms of HCV-associated BCP [i.e. mixed cryoglobulin (MC), rheumatoid factor (RF) and systemic vasculitis].

A total of 76 HCV-infected patients (HCV RNA+) were compared with 13 healthy volunteers. Epidemiological, clinical, immunochemical and virological data were prospectively collected. BLyS serum levels were assessed by an ELISA sandwich method.

Of the 76 patients, 38 females, 38 males, mean age 53 +/- 15 yrs; 47 (62%) patients had type II (27 patients) or type III MC (20 patients); 27 (35.5%) patients had HCV-systemic vasculitis. BLyS serum levels tended to be higher in HCV-infected patients than in healthy controls (1.8 +/- 0.9 vs 1.5 +/- 0.2 ng/ml), were higher in patients with MC than without (2.03 +/- 1.02 vs 1.5 +/- 0.5 ng/ml; P = 0.008), and even higher in type II than type III MC (2.3 +/- 1.2 vs 1.7 +/- 0.6 ng/ml; P = 0.03). There was a correlation between BLyS and MC serum levels (R = 0.4; P = 0.004). BLyS serum levels were higher in patients with a positive RF than in those without (2.06 +/- 1.09 vs 1.6 +/- 0.56 ng/ml, P = 0.035), and with systemic vasculitis than in those without (2.24 +/- 1.16 vs 1.6 +/- 0.6 ng/ml; P = 0.006).

BLyS serum levels are significantly correlated with B-cell proliferation during chronic HCV infection. These results strongly suggest a role for BLyS in the induction and expression of HCV-BCP.