Decreased B cell activating factor receptor expression on peripheral lymphocytes associated with increased disease activity in primary Sjogren's syndrome and systemic lupus erythematosus

Objective: To analyse B cell activating factor (BAFF) receptor (BAFF-R) expression on peripheral lymphocytes from patients with primary Sjogren's syndrome (pSS) and systemic lupus erythematosus (SLE). Patients and methods: Peripheral blood mononuclear cells from 20 patients with pSS, 19 patients with SLE and 15 controls were examined by flow cytometry to investigate BAFF-R mean fluorescence intensity (MFI) on lymphocytes. BAFF-R mRNA level from isolated blood B cells of nine patients with pSS and eight controls was assessed by real-time quantitative reverse transcription-PCR. BAFF serum level was determined by ELISA. Results: In all subjects, BAFF-R was expressed on all naive CD272 and memory CD27+ B- cells and was present on 0.5% of T cells. The expression of BAFF-R on B cells was significantly decreased in patients with pSS as compared with controls (MFI = 7.8 vs 10.6, p = 0.001), and was intermediate in patients with SLE (MFI = 9.5). Serum BAFF level was inversely correlated with BAFF-R MFI ( p = 0.007), but not because of competition between endogenous BAFF (at observed concentrations in patients) and the monoclonal antibody (11C1) detecting BAFF-R. BAFF-R mRNA levels did not differ between patients with pSS and controls (p = 0.48). BAFF-R MFI decreased after overnight culture with recombinant human BAFF (from 32.5 to 25.4, p = 0.03). Contrary to the serum BAFF level, BAFF-R expression was correlated with extraglandular involvement in pSS and SLE Disease Activity Index. Conclusions: BAFF-R expression is reduced on peripheral B cells of patients with pSS and SLE. This downregulation occurs through a post-transcriptional mechanism and could be the consequence of chronic increase in BAFF. BAFF-R levels on B cells could be a novel activity biomarker in autoimmune diseases.