TWEAK-binding autoantibodies are generated during psoriatic arthritis and are not influenced by anti-TNF therapy

Abstract

Background: TNF weakly inducer of apoptosis (TWEAK) is member of the TNF ligand superfamily. Various data support that TWEAK produced by synovial macrophages may contribute to synovitis observed in psoriatic arthritis (PsoA). In PsoA, anti-TNF therapy has been successful in agreement with the key role of TNF in the pathogenesis and the generation by PsoA patients of anti-TNF autoantibodies referred as "beneficial autoimmunity to pro-inflammatory mediators". However, the role of TNF-alpha in the regulation of TWEAK modulation of inflammation during PsoA remains unknown.

Methods: We have studied level course during anti-TNF therapy of serum soluble TWEAK. In the same cohort, we have investigated the generation of TWEAK-binding autoantibodies by PsoA patients before and after anti-TNF therapy.

Results: Patients with PsoA had significantly higher serum levels of TWEAK compared with controls [respective means (±SEM) were 645 pg/ml (64) and 467 pg/ml (23); (p = 0.006)] but serum soluble TWEAK levels were not correlated with BASDAI (Spearman's coefficients <0.003, p > 0.05). Our study showed that soluble TWEAK levels were not modulated by etanercept therapy [respective Means (±SEM) were 605 (95) (week 12) and 744 (97) (week 24) pg/ml; (p > 0.23)]. Anti-TWEAK autoantibodies were detected in 9/13 (69.2 %) PsoA patients at inclusion and only in 3/57 (5.3 %) healthy blood donors (p < 0.0001). These circulating antibodies were persistent in PsoA patients and detected at similar levels during etanercept therapy. Moreover we showed that they had a down regulating effect on CCL-2 secretion by endothelial cells stimulated by rh TWEAK in vitro.

Conclusion: Our study revealed that during psoriatic arthritis (1) serum TWEAK was up regulated and (2) TWEAK-binding autoantibodies are generated. Both parameters were not influenced by anti-TNF therapy and persisted at high levels during anti-TNF therapy. For the first time we described here TWEAK-binding IgG autoantibodies with a down regulating effect on CCL-2 secretion by endothelial cells stimulated by rh TWEAK in vitro. Finally, our results suggest that TWEAK may be involved in PsoA pathogeny. Trial registration This clinical trial was approved by the local Ethics Committee "Comité de Protection des Personnes Sud-Méditerranée V" with the registration number: 2011-002954-29, and French health minister registration number AFSSAPS A110784-42 obtained the 08/22/2011. This clinical trial is registered in Clinical trial.gov under the number: NCT02164214.

Keywords: Anti-TNF therapy; Anti-cytokine; Autoantibodies; Psoriatic arthritis; TWEAK.

Figures

Fig. 1

Serum TWEAK levels in patients with PsoA (n = 13) and controls (n = 57). Serum samples have been collected at baseline and 12 and 24 weeks after the initiation of etanercept therapy. TWEAK levels have been evaluated with a commercially available ELISA kit. a Median is indicated for each group as a black line in the box. b Evolution over time of TWEAK levels is represented for each patient

Fig. 2

Relationship of serum TWEAK level to response to anti-TNF treatment. Responders (n = 10) are defined as patients with a minimal decrease of BASDAI of 50 % or 2 points at 12th week of treatment. Black lines in the box indicate the median of values

Fig. 3

Detection of serum anti-TWEAK auto-antibodies. a Western blot assay using recombinant human TWEAK. Line 1 Positive patient with PsoA. Line 2 Negative patient with PsoA. Line 3 Negative control serum. On line 1, 2 and 3, sera are 1:50 diluted. Line 4 Positive control based on revelation with a commercially available polyclonal anti-TWEAK antibody. Line 5 Negative control based on serum omission. b Immunofluorescence test. Serum are incubated on wild-type HEK cells and on TWEAK-transfected HEK cells. Membrane and cytoplasmic fluorescence staining patterns specifically observed with an anti-TWEAK antibody positive patient serum only on the transfected wells are indicated by white arrows

Fig. 4

Evolution over time of serum anti-TWEAK auto-antibody titers in positive PsoA patients. a Titers of auto-antibodies have been obtained by serial dilutions (1:50, 1:100, 1:200, 1:400, 1:800, 1:1000) of screening positive samples (n = 9) tested with our home made western blot assay using recombinant human TWEAK. Samples with titers above 1000 are indicated by a grey arrow. b The images of each membrane according to the serial dilution are represented for a patient exhibiting TWEAK-binding IgG at a titer of 800

Fig. 5

Relationship of serum TWEAK levels or anti-TWEAK antibody levels to disease duration and BASDAI. Spearman’s correlation analysis was used to test for correlations. Spearman coefficients (r) and p values (p) are indicated in each plot

Fig. 6

Down regulation by TWEAK-binding IgGs of the in vitro endothelium CCL-2 secretion. ELISA analysis of CCL-2 levels in the supernatants of HUVECs stimulated by TWEAK (100 ng/ml) or not (medium) and co-incubated with a commercially available goat polyclonal blocking anti-TWEAK antibody (5 µg/ml) or with purified human serum IgG negative for TWEAK-binding IgG test (50 ng/ml) or with purified PsoA patient TWEAK-binding IgG (50 ng/ml). Note the downregulation of the increased secretion of CCL-2 under TWEAK exposure when cells are incubated with purified PsoA patient TWEAK-binding IgG. *p