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

OBJECTIVE: 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].
METHODS: 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.
RESULTS: 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).
CONCLUSION: 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.