Increased levels of anti-dsDNA antibodies in immune complexes before treatment with belimumab associate with clinical response in patients with systemic lupus erythematosus

Abstract

Introduction: Immune complexes are of importance in systemic lupus erythematosus pathogenesis, and autoantibodies are believed to participate in immune complex formation. Quantification of autoantibody levels in circulating IC might be of prognostic value.

Methods: A C1q-binding-eluting technique was applied to purify immune complexes from 55 belimumab-treated systemic lupus erythematosus patients during a 24-month follow-up. Autoantibodies in serum and in solubilized immune complexes were quantified using addressable laser bead immunoassay. We investigated whether levels of autoantibodies in immune complexes associate with disease activity and response to belimumab treatment.

Results: High baseline anti-double-stranded DNA and anti-histone levels in immune complexes associated with attainment of zero scores in clinical systemic lupus erythematosus disease activity index 2000 during the 24-month follow-up (p = 0.003 and p = 0.048, respectively). Low complement levels associated with high serum anti-double-stranded DNA and anti-ribosomal P levels (p = 0.003 and p = 0.008, respectively) and high anti-double-stranded DNA (p = 0.002) but not anti-ribosomal P levels in immune complexes. Anti-SSA/SSB serum levels were lower in patients attaining lupus low disease activity state at month 6; these associations were stronger for corresponding immune complex levels. Serum levels of most autoantibodies had declined at month 3, whereas autoantibody levels in immune complexes, except for anti-double-stranded DNA, showed a more gradual decline over 1-2 years. Serum anti-double-stranded DNA levels decreased in all patients irrespective of systemic lupus erythematosus disease activity index 2000=0 attainment, whereas immune complex levels decreased only in achievers.

Conclusion: Immune complex levels of autoantibodies against double-stranded DNA and the SSA/SSB complex show more specific associations with treatment outcome compared with serum levels in belimumab-treated systemic lupus erythematosus patients. Characterization of autoantibody content in circulating immune complexes could prove useful in treatment evaluation in systemic lupus erythematosus and other immune complex-associated diseases.

Keywords: Anti-double-stranded DNA; Anti-nuclear autoantibodies; Belimumab; Immune complexes; Systemic lupus erythematosus; Therapy response.

Fig. 1

Distribution and levels of autoantibodies in sera (a, e) and corresponding solubilized IC fractions (b, f) for patients (a, b) and 20 healthy controls (e, f). Levels are presented in arbitrary units (AU/mL) for all antibodies except for anti-dsDNA, which is presented in international units (IU/mL). The ratio between autoantibody levels in IC and conventional measurement in sera among the patients are presented as c percentage in IC as compared to sera and d as enrichment after correction for total IgG concentrations in IC and sera, respectively. Median levels are illustrated as horizontal solid lines and the corresponding values are stated below each panel. The horizontal dotted line in a and e shows the clinically recommended cutoff values for autoantibodies in serum (40 U/mL). a, e The prevalence (%) of specific autoantibodies in serum is presented above each antibody. Values below the measurement ranges are depicted as 0.1 for sera and 0.01 in IC. Ribo P ribosomal P

Fig. 2

Associations between levels of complement protein C3 and/or C4 and levels of a, b anti-dsDNA and c, d anti-ribosomal P antigen antibodies in a, c sera obtained with conventional measurement and b, d in corresponding solubilized IC. e Levels of C1q-binding IC in 54/55 of the investigated patients, compared to a population-based non-SLE control group. Horizontal lines indicate median levels, with the corresponding figures shown below each group. ns not significant

Fig. 3

Associations between attainment of cSLEDAI-2K=0 ever during the 2-year follow-up period and levels of a, b anti-dsDNA and c, d anti-ribosomal P antigen in a, c serum obtained with conventional measurement and b, d in the corresponding solubilized IC. Horizontal lines indicate median values of each antibody, with the corresponding figures shown below each measure. ns not significant, Rib P ribosomal P antigen

Fig. 4

Associations between attainment of LLDAS after 6 months and levels of a, b anti-SSA/Ro52, c, d anti-SSA/Ro60, and e, f anti-SSB/La in a, c, e sera where data were obtained with conventional measurements and b, d, f in the corresponding solubilized IC. Horizontal lines illustrate median levels, with corresponding values presented below each measure. ns not significant, LLDAS low lupus disease activity state

Fig. 5

Changes in anti-dsDNA levels a in sera where data were obtained with conventional measurements and b in solubilized IC for the belimumab-treated SLE patients, in relation to therapy response. In each panel, data are shown for all 53 patients with full data to the left, for the 22 patients not attaining cSLEDAI-2K=0 in the middle, and for the 31 patients attaining cSLEDAI-2K=0 to the right. Horizontal bars represent median values, which are also presented below each measure