Associations of B cell-activating factor (BAFF) and anti-BAFF autoantibodies with disease activity in multi-ethnic Asian systemic lupus erythematosus patients in Singapore

Abstract

To measure the levels of B cell-activating factor (BAFF) and endogenous anti-BAFF autoantibodies in a cohort of multi-ethnic Asian systemic lupus erythematosus (SLE) patients in Singapore, to determine their correlation with disease activity. Serum samples from 121 SLE patients and 24 age- and sex-matched healthy controls were assayed for BAFF and anti-BAFF immunoglobulin (Ig)G antibody levels by enzyme-linked immunosorbent assay (ELISA). The lowest reliable detection limit for anti-BAFF-IgG antibody levels was defined as 2 standard deviations (s.d.) from blank. Correlation of serum BAFF and anti-BAFF IgG levels with disease activity [scored by SLE Activity Measure revised (SLAM-R)], and disease manifestations were determined in these 121 patients. SLE patients had elevated BAFF levels compared to controls; mean 820 ± 40 pg/ml and 152 pg ± 45/ml, respectively [mean ± standard error of the mean (s.e.m.), P < 0·01], which were correlated positively with anti-dsDNA antibody levels (r = 0·253, P < 0·03), and SLAM-R scores (r = 0·627, P < 0·01). In addition, SLE patients had significantly higher levels of anti-BAFF IgG, which were correlated negatively with disease activity (r = –0·436, P < 0·01), levels of anti-dsDNA antibody (r = –0·347, P < 0·02) and BAFF (r = –0·459, P < 0·01). The majority of patients in this multi-ethnic Asian SLE cohort had elevated levels of BAFF and anti-BAFF antibodies. Anti-BAFF autoantibody levels correlated negatively with clinical disease activity, anti-dsDNA and BAFF levels, suggesting that they may be disease-modifying. Our results provide further information about the complexity of BAFF pathophysiology in different SLE disease populations and phenotypes, and suggest that studies of the influence of anti-cytokine antibodies in different SLE populations will be required when selecting patients for trials using targeted anti-cytokine therapies.