Multi‐Autoantibody Testing Identifies Expansion of Reactivity to Targeted Antigens Before a Diagnosis of Rheumatoid Arthritis

Abstract

Objective Rheumatoid arthritis (RA) has a “pre‐RA” period in which multiple autoantibodies, including antibodies to citrullinated (cit) proteins (ACPA), rheumatoid factor (RF), anti–peptidyl arginine deiminase (anti‐PAD), among others, have been described; however, few studies have tested all autoantibodies in a single pre‐RA cohort. This study aims to evaluate the prevalence of multiple autoantibodies in pre‐RA and potentially identify an autoantibody profile in pre‐RA that indicates imminent onset of clinical RA. Methods We evaluated 148 individuals with two pre‐ and one post‐RA diagnosis samples available from the Department of Defense Serum Repository and matched controls. Samples were tested for immuglobulin (Ig) G anti–cyclic cit peptide‐3 (anti‐CCP3), five ACPA fine specificities, five anti‐PAD isoforms, as well as RF IgA and RF IgM using commercial platforms; cutoffs were determined using levels present in <1% of controls. Results Positivity of anti‐CCP3, RF IgA and RF IgM, anti‐PAD1, anti–cit‐vimentin 2, anti–cit‐fibrinogen, and anti–cit‐histone 1 increased over time in pre‐RA, although anti‐PAD and ACPA fine specificities were predominately present within anti‐CCP3–positive individuals. Within anti‐CCP3–positive samples from the pre‐RA period, positivity for RFs as well as anti‐PAD and ACPA fine specificities classified samples as being closer to the time of RA diagnosis. Conclusion Multiple autoantibodies are present in pre‐RA and increase in positivity as the time of RA diagnosis approaches. These results confirm previous findings predicting imminent RA and provide a pathway using commercial‐grade assays to assess the risk for and timing of development of clinical RA.