Citrullination Is Not a Determinant in the Lack of Tolerance to Peptidylarginine Deiminase 2 and 4 in Rheumatoid Arthritis

Pooja Naik¹, Ryan Davis², Jon T. Giles³, Felipe Andrade⁴ and Erika Darrah⁵, ¹Department of Medicine, Division of Rheumatology, Johns Hopkins University School of Medicine, Baltimore, MD, ²Division of Rheumatology, Johns Hopkins University School of Medicine, Baltimore, MD, ³Columbia University, New York, NY, ⁴Medicine/Rheumatology, Johns Hopkins University School of Medicine, Baltimore, MD, ⁵Department of Medicine/Division of Rheumatology, Johns Hopkins University School of Medicine, Baltimore, MD

Meeting: 2018 ACR/ARHP Annual Meeting

Keywords: autoantibodies, autoantigens, citrullination and rheumatoid arthritis (RA), PAD

Session Information

Date: Tuesday, October 23, 2018

Session Title: Rheumatoid Arthritis – Etiology and Pathogenesis Poster III

Session Type: ACR Poster Session C

Session Time: 9:00AM-11:00AM

Background/Purpose: Peptidylarginine deiminase (PAD) 2 and 4 are targets of the humoral response in RA. However, the mechanisms by which these enzymes become immunogenic in this disease are still unknown. In addition of catalyzing the conversion of arginine residues to citrulline in a broad range of substrates, these enzymes also autocitrullinate. Since citrullination is a major determinant in the lack of tolerance to autoantigens in RA, we investigated whether PAD2 and PAD4 may also be part of the anti-citrullinated protein autoantibody (ACPA) response in this disease.

Methods: We determined the prevalence of antibodies against auto-citrullinated PAD2 and PAD4 in 184 patients with established RA. ELISA assays were developed to screen sera from RA patients and healthy controls for reactivity to native and citrullinated PADs. Antibody binding to native and citrullinated PADs was compared and confirmed in blocking experiments. Recognition of native vs. citrullinated PAD at the individual level was plotted and analyzed by linear regression.

Results: Anti-native PAD4 and anti-native PAD2 antibodies were present in 42% and 18.5% of patients in the cohort, respectively. Autoantibodies against PAD4 bound similarly to both the native and citrullinated form such that anti-PAD4 levels against the citrullinated form positively correlated with that against the native form (R square = 0.863; p = <0.0001). Only two sera were identified that bound exclusively to citrullinated PAD4. Similar results were obtained for binding of autoantibodies to the native and citrullinated forms of PAD2 (R square = 0.908; p = <0.0001), with only four sera exclusively binding to citrullinated PAD2. Pre-incubation of sera with native PAD4 or PAD2 in solution significantly reduced antibody binding to the respective citrullinated protein (p ≤ 0.0001).

Conclusion: Taken together, this study demonstrates that citrullination is not a major determinant in the breech of tolerance to PAD2 and PAD4 in RA. Although PADs are necessary for the production of ACPAs, the data suggest that anti-PAD autoantibodies and ACPAs are likely driven by distinct pathogenic mechanisms.

Disclosure: P. Naik, None; R. Davis, None; J. T. Giles, None, 7; F. Andrade, Medimmune; Pfizer; BMS, 2, 5, 7; E. Darrah, Medimmune, Pfizer, Padlock Therapeutics,, 2, 5, 7.

To cite this abstract in AMA style:

Naik P, Davis R, Giles JT, Andrade F, Darrah E. Citrullination Is Not a Determinant in the Lack of Tolerance to Peptidylarginine Deiminase 2 and 4 in Rheumatoid Arthritis [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 10). https://acrabstracts.org/abstract/citrullination-is-not-a-determinant-in-the-lack-of-tolerance-to-peptidylarginine-deiminase-2-and-4-in-rheumatoid-arthritis/. Accessed January 25, 2021.

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