Differential peripheral B cell phenotype in patients with primary Sjögren’s syndrome (pSS) compared to secondary Sjögren’s syndrome associated with systemic lupus erythematosus (SS/SLE)

Abstract

Introduction: Peripheral B-cell abnormalities, a feature of both systemic lupus erythematosus (SLE) and primary Sjogren’s syndrome (pSS), are implicated in the pathogenesis of both diseases and correlate with disease activity. This study aims to investigate how the defective B-cell phenotype in pSS patients compares to patients with SS and SLE (SS/SLE), and whether abnormalities in B-cell phenotype could be related to differential B-cell lipid-raft expression and B-cell activating factor (BAFF) receptor function in patients with pSS and SLE and secondary SS (SS/SLE). Methods: Blood samples and clinical and laboratory parameters from 32 patients with pSS and SS/SLE and 13 age/sex matched HC were obtained. We used flow-cytometry to perform B-cell immunophenotyping and analysed lipid-raft expression (marker of B-cell activation). In vitro cultures were also used to assess lipid-raft expression in response to BAFF. Results: Patients with SS/SLE had a significantly decreased Bm1 and Bm5 and increased Bm2 populations compared to HC (p=0.031, p=0.035 and p=0.01, respectively), and increased Bm2 compared to pSS (p=0.027). Bm1-cells were decreased in both pSS and SS/SLE patients compared to HC (p=0.028 and p= 0.031, respectively). Both age and disease duration correlated strongly with Bm2’ cells in SS/SLE patients (r=0.9572, p= 0.0428), and the immunosuppressive treatment correlated negatively with the number of circulating Bm2 and Bm2’ cell in pSS (r = -0.54, p=0.01 and r = -0.56, p=0.008, respectively). B-cells from patients with pSS had a significant increase in lipid-raft expression compared to HC (p=0.01) and patients with SS/SLE (p<0.05). Lipid-raft levels correlated with BAFF-receptor expression in HC and SS/SLE B-cells (p=0.17, r=0.694) but not in pSS patients. Both disease activity score (ESSDAI) and IgG level correlated positively with lipid rafts expression in B cells from patients with pSS (r = 0.79, p=0.004 and r =0.53, p=0.04, respectively). Conclusion: Patients with SS/SLE had more significant B-cell abnormalities compared to HC and pSS, detectable even in a small number of patients. Also the relationship between lipid-raft and BAFF-receptor expression was altered between pSS and SS/SLE patients, and correlated with the disease activity and IgG levels in pSS group, suggesting that therapies targeting BAFF might be particularly successful in the SS/SLE sub-group of patients