Anti-peptidylarginine deiminase-4 antibodies at mucosal sites can activate peptidylarginine deiminase-4 enzyme activity in rheumatoid arthritis

• Published in: Arthritis research & therapy Vol. 23; no. 1; pp. 1 - 163
• Main Authors: Demoruelle, M. Kristen, Wang, Hong, Davis, Ryan L, Visser, Ashley, Hoang, Johnny, Norris, Jill M, Holers, V. Michael, Deane, Kevin D, Darrah, Erika
• Format: Journal Article
• Language: English
• Published: London BioMed Central Ltd 06.06.2021; BioMed Central; BMC
• Subjects: Anti-PAD4 antibodies; Antibodies; Arthritis; Autoantibodies; Development and progression; Diagnosis; Enzymes; Health aspects; Lung; Lung diseases; Oral mucosa; Pathogenesis; Peptides; Proteins; Respiratory mucosa; Rheumatoid arthritis; Risk factors; Saliva; Sputum; United States; United States > US
• ISSN: 1478-6362; 1478-6354; 1478-6362
• DOI: 10.1186/s13075-021-02528-5

Background Mucosal sites are hypothesized to play a role in the development of rheumatoid arthritis (RA). Since serum anti-peptidylarginine deiminase (PAD)4 antibodies, including a subset that cross-react with PAD3 (PAD3/4), are specific for RA and associate with severe disease, we sought to examine whether anti-PAD4 and anti-PAD3/4 antibodies were present in the lung and oral mucosa of subjects with RA and "at-risk" for RA. Methods We included 37 RA, 25 healthy control, and 46 subjects "at-risk" for RA based on familial RA and/or serum anti-citrullinated protein antibody (ACPA) positivity. Paired serum, sputum, and saliva were evaluated for anti-PAD4 and anti-PAD3/4 using immunoprecipitation and ACPA using ELISA. Immunoglobulins (Ig) were purified from representative samples, and their effect on citrullination of histone H3 by recombinant human PAD4 was measured by anti-citH3 immunoblot. Results Anti-PAD4 antibodies were detected in the serum of 6/37 (16.2%), sputum of 3/37 (8.1%), and saliva of 3/33 (9.1%) RA subjects and in the serum and sputum of 1/46 (2.2%) at-risk subjects. None of the healthy controls had anti-PAD4 antibodies at any site. Serum, sputum, and salivary anti-PAD4 antibodies were more prevalent in RA subjects with RA duration >2 years. Purified antibodies from representative anti-PAD4-positive and anti-PAD3/4-positive sputum were primarily of the IgA isotype and able to increase PAD4 enzymatic activity. Conclusions Anti-PAD4 antibodies are present in the sputum and saliva of a portion of RA patients and are infrequent in at-risk subjects. Importantly, the ability of anti-PAD4, and particularly anti-PAD3/4, antibodies in the sputum to enhance PAD4 enzymatic activity suggests that anti-PAD4 may play an active role in the RA lung. Keywords: Rheumatoid arthritis, Anti-PAD4 antibodies, Lung, Sputum, Saliva