Correlation of serum B lymphocyte stimulator and β2 microglobulin with autoantibody secretion and systemic involvement in primary Sjogren's syndrome

Background: In primary Sjogren's syndrome ( pSS), extraglandular involvement might result from more intense stimulation of autoreactive B cells. Thus markers of B cell activation could be useful in the clinical assessment of this disease. Objective: To investigate the association of serum B lymphocyte stimulator ( BLyS) and beta(2) microglobulin with autoantibody production and extraglandular involvement in pSS. Methods: Serum concentrations of BLyS and beta(2) microglobulin were analysed in 177 patients with pSS according to the American - European consensus group criteria. Serum beta(2) microglobulin was determined serially in 25 patients. Results: Autoantibody secretion ( presence of anti-SSA antibody alone or of both anti-SSA and anti-SSB) was associated with increased serum BLyS and beta(2) microglobulin. No correlation was found between BLyS and beta(2) microglobulin levels ( p = 0.36). Serum concentrations of beta(2) microglobulin and C reactive protein and positive anti-SSB antibody results were associated with extraglandular involvement on univariate analysis ( p< 10(-4), p = 0.003, and p = 0.004, respectively). Serum beta(2) microglobulin was also significantly increased in patients with extraglandular involvement without autoantibodies ( mean (SD): 1.75 (0.7) v 1.39 (0.5) mg/l, p = 0.039). Multivariate analysis showed that extraglandular involvement was associated only with increased serum beta(2) microglobulin ( p = 0.035, odds ratio = 2.78 (95% confidence interval, 1.07 to 7.22)). Among the 25 patients who had serial determinations of serum beta(2) microglobulin, the concentrations were increased in all those with disease flare and decreased in three following treatment. Serum BLyS, gamma globulin, IgG, and rheumatoid factor levels were not associated with features of systemic involvement. Conclusions: Serum beta(2) microglobulin and BLyS reflect B cell activation in different ways in pSS. Serum beta(2) microglobulin assessment could be helpful as an activity marker in pSS.