Immune complexes containing serum B-cell activating factor and immunoglobulin G correlate with disease activity in systemic lupus erythematosus.

Methods: Levels of serum BAFF, IgG anti-BAFF and BAFF-IgG complexes were quantified by enzyme-linked immunosorbent assay. IgG anti-BAFF and BAFF-IgG complexes were further characterized using serum fractions obtained by fast protein liquid chromatography. To study the association of serum BAFF, IgG anti-BAFF and BAFF-IgG complex levels with SLE manifestations, 373 visits from 178 patients prospectively included in the Swiss SLE Cohort Study were analysed.

Results: While IgG anti-BAFF levels were not associated with clinical manifestations of SLE, serum BAFF levels correlated with disease activity and were higher in patients with renal involvement. Interestingly, we could also demonstrate the occurrence of BAFF-IgG complexes of different sizes in the sera of SLE patients, which were not due to treatment with belimumab and differed from complexes constructed in vitro. Most strikingly, the levels of these BAFF-IgG complexes were found to strongly correlate with overall disease activity, low complement levels and a history of lupus nephritis.

Conclusion: BAFF-IgG complexes strongly correlate with disease activity in SLE patients, suggesting a pathogenic role in SLE.