Background/Purpose: Malondialdehyde (MDA) is a naturally occurring reactive aldehyde that arises during apoptosis or as a consequence of elevated reactive oxygen species and lipid peroxidation. Free MDA can post-translationally modify lysine residues in a protein carbonylation process that generates neo-epitopes that can be recognized by autoantibodies.

Methods: Serum IgG anti-MDA levels were compared in 71 healthy controls, 30 OA, and 283 SLE and 162 RA patients, identified by ACR criteria. IgG anti-MDA was measured by sandwich ELISA using MDA-modified BSA. After flow cytometry sorting of RA synovial memory B cells, and single cell Ab-gene PCR, 114 mAbs were expressed and tested for MDA-reactivity. Analyses used the 2-sided Mann-Whitney test or Spearman correlation.

Results: In sera, IgG anti-MDA was significantly increased in SLE (17±21 RU/ml, p<0.0001) and RA patients (13±11 RU/ml, p<0.0001), compared to controls (5±3 RU/ml). In SLE, IgG anti-MDA correlated with disease activity by SELENA-SLEDAI (p<0.0001, R=0.34, n=219). Levels were also significantly higher in SLE patients with active disease (SLEDAI≥6, 18.9±17.3 RU/ml, p=0.001) than with low disease activity (SLEDAI<6, 11.5±16.6). In RA patients, IgG anti-MDA correlated with DAS28-ESR (p<0.0001, R=0.35, n=157). Compared to RA patients with low disease activity (DAS28<3.2, 6±3), levels were significantly increased in RA with moderate activity (DAS28 3.2-5.1, 12±11 RU/ml, p=0.005) and high activity (DAS28>5.1, 15±12 RU/ml, p=0.001). In DMARD naïve RA (n=62), IgG anti-MDA also correlated with serum TNFα (p=0.002, R=0.39), IL-6 (p=0.03, R=0.27), and CRP levels (p=0.003, R=0.37). In RA synovial mAbs, we identified four clones (3.5%) that recognized MDA-modified epitopes. The most reactive clone, 1276:01F04, showed high specific binding to MDA but was non-reactive with carbamylated or 4-HNE-modifications. Specificity was confirmed in antigen-competition studies with MDA or MDA acetaldehyde (MAA) protein adducts. This mAb also bound MDA-modified human fibrinogen and albumin. No cross-reactivity with citrullinated epitopes was detected, and mAbs with ACPA or RF reactivity did not bind MDA. Notably, 1276:01F04 originated from an IgG1-bearing B cell that was encoded by near germline variable genes (VH4-39, 1 R-mutation in HCDR3; VL1-51, 2 S-mutations in FR1).

Conclusion: IgM binding to MDA-adducts may be common in health from birth and are part of the natural antibody pool. Yet, IgG anti-MDA are associated with inflammatory conditions including increased disease activity in autoimmune patients. Importantly, MDA-autoreactive B cells could also be isolated from RA synovium, the site of disease. Further studies are merited to investigate the potential pathogenic properties of IgG anti-MDA B-cells/autoantibodies.

« Back to 2016 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/disease-activity-associated-autoantibodies-to-malondialdehyde-modified-proteins-can-be-isolated-from-synovial-b-cells-in-ra/