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

Rheumatology 2007;46:65–69 Advance Access publication 16 June 2006 doi:10.1093/rheumatology/kel177 Concise Report Hepatitis C virus-associated B-cell proliferation—the role of serum B lymphocyte stimulator (BLyS/BAFF) D. Sène, N. Limal, P. Ghillani-Dalbin1, D. Saadoun, J.-C. Piette and P. Cacoub 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 RNAþ) 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 ¼ 0.008), and even higher in type II than type III MC (2.3
1.2 vs 1.7
0.6 ng/ml; P ¼ 0.03). There was a correlation between BLyS and MC serum levels (R ¼ 0.4; P ¼ 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 ¼ 0.035), and with systemic vasculitis than in those without (2.24
1.16 vs 1.6
0.6 ng/ml; P ¼ 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. KEY WORDS: BLyS (BAFF), HCV, B-cell proliferation, Mixed cryoglobulinaemia. Hepatitis C virus (HCV) infection, a worldwide disease, is strikingly associated with several extra-hepatic manifestations. Most of these are related to B-cell proliferative disorders. The most common is mixed cryoglobulins (MCs), which occur in about half of the HCV-infected patients [1–4]. The MCs are classified according to the presence or absence of a monoclonal component among other polyclonal immunoglobulins (Igs) in the serum cryoprecipitate: type II MC in the presence of a monoclonal component and type III MC when only polyclonal Igs are present [5]. There is evidence showing that type II MC is characterized by a monoclonal and/or oligoclonal proliferation of B-cells in bone marrow, liver tissue and peripheral blood [6–8]. These clonal B-cells are responsible for the production of monoclonal IgM, which displays anti-IgG rheumatoid factor (RF) activity. The monoclonal IgM-RF is the major component of the MC cryoprecipitate in addition to anti-HCV-antibodies, HCV viral particles and lipoproteins [1, 9]. In addition to MC and RF, HCV infection is also associated with the production of anti-nuclear and anti-cardiolipid antibodies, which reflect chronic non-specific B-cell proliferation and antigen-driven stimulation [4, 10–13]. Peculiar clinical features are also associated with HCV-infection, including B-cell lymphoma [14] and the association with a Sjögren-like syndrome. Although some data suggest that an overexpression of the anti-apoptotic Bcl2 protein family [15–17] or an antigen-driven process [18–20] are involved, the mechanisms through which B-cell proliferation (BCP) may occur during HCV infection remain to be elucidated. Knowledge of the mechanisms underlying BCP and B-cell survival pathways has been strengthened since the identification of B lymphocyte stimulator (BLyS), also called B-cell activating factor (BAFF) or tumour necrosis factor (TNF)- and Apo-Lrelated leucocyte-expressed ligand-1 (TALL-1) [21, 22]. BLyS is a 285 amino acid protein encoded by a gene on chromosome 13q32–34 and secreted by myeloid cells including monocytes, macrophages, dendritic and activated B-cells [21, 23]. Three receptors for BLyS have been identified: (i) B-cell maturation antigen (BCMA), (ii) transmembrane activator and calciummodulating cyclophilin ligand (CAML) interactor (TACI) and (iii) more recently, B-cell-activating factor receptor (BAFF-R). BCMA and BAFF-R are predominantly expressed on B lymphocytes, whereas TACI can be found on B-cells and activated T-cells [21, 24–27]. Several studies have shown strong evidence of the pivotal role of BLyS in BCP and the related haematological and autoimmune diseases. Transgenic mice overexpressing BLyS developed critical BCP in blood and marginal zones of lymph nodes, with the production of high titres of Igs, RF, anti-DNA Department of Internal Medicine and 1Department of Immunochemistry, La Pitié-Salpêtrière Hospital, 47-83 Boulevard de l’Hôpital, 75651 Paris cedex 13, France. Received 13 March 2006; revised version accepted 18 April 2006. Correspondence to: Prof. Patrice Cacoub, MD, Service de Médecine Interne, Hôpital La Pitié-Salpêtrière, 83 Boulevard de l’Hôpital, 75651 Paris Cedex 13, France. E-mail: 65 ß The Author 2006. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: 66 D. Sène et al. antibodies and sometimes cryoglobulin [25, 28–30]. While ageing, these mice also developed lupus-like or Sjögren-like syndromes [30]. In human haematological diseases, a high BLyS expression has been found in non-Hodgkin’s lymphomas (mainly follicular lymphoma) and myeloma [31–33]. Raised serum levels of BLyS have also been demonstrated in autoimmune diseases, such as systemic lupus, systemic sclerosis, rheumatoid arthritis and Sjögren’s syndrome [34–38]. We hypothesized a potential role for BLyS in HCV-related BCP, and examined the BLyS serum levels in HCV-infected patients. Our results demonstrate that BLyS serum levels in HCV-infected patients are markedly elevated in patients with MC, mainly in those with type II MC, with a positive RF and systemic vasculitis. TABLE 1. Main characteristics of the study population Age (yrs)* Sex ratio (M/F) HCV genotype, n (%) 1 2 or 3 4 or 5 Disease duration (for 43 patients) (yrs)* METAVIR fibrosis score* METAVIR F3–F4, n (%) METAVIR F4 (cirrhosis) METAVIR activity score* Mixed cryoglobulin (MC), n (%) Type II, n (%) Type III, n (%) Positive rheumatoid factor, n (%) MC systemic vasculitis, n (%) 53.2
15.1 38/38 72/76 (94.7) 41/72 (56.9) 18 (25) 13 (18.1) 23.2
8 1.7
1.2 16/73 (21.9) 10/73 (13.7) 1.1
0.6 47 (61.8) 27 (57) 20 (43) 38/70 (54.3) 27 (35.5) Patients and methods The design of this study was approved by the local ethical committee as conformed to the current standards and a written consent was obtained from all the patients and volunteers. A total of (...truncated)