Autoantibodies to two novel peptides in seronegative and early rheumatoid arthritis

Abstract

Objectives: Despite recent progress in biomarker discovery for RA diagnostics, still over one-third of RA patients-and even more in early disease-present without RF or ACPA. The aim of this study was to confirm the presence of previously identified autoantibodies to novel Hasselt University (UH) peptides in early and seronegative RA.

Methods: Screening for antibodies against novel UH peptides UH-RA.1, UH-RA.9, UH-RA.14 and UH-RA.21, was performed in two large independent cohorts. Peptide ELISAs were developed to screen for the presence of antibodies to UH-RA peptides. First, 292 RA patients (including 39 early patients), 90 rheumatic and 97 healthy controls from UH were studied. Antibody reactivity to two peptides (UH-RA.1 and UH-RA.21) was also evaluated in 600 RA patients, 309 patients with undifferentiated arthritis and 157 rheumatic controls from the Leiden Early Arthritis Clinic cohort.

Results: In both cohorts, 38% of RA patients were seronegative for RF and ACPA. Testing for autoantibodies to UH-RA.1 and UH-RA.21 reduced the serological gap from 38% to 29% in the UH cohort (P = 0.03) and from 38% to 32% in the Leiden Early Arthritis Clinic cohort (P = 0.01). Furthermore, 19-33% of early RA patients carried antibodies to these peptides. Specificities in rheumatic controls ranged from 82 to 96%. Whereas antibodies against UH-RA.1 were related to remission, anti-UH-RA.21 antibodies were associated with inflammation, joint erosion and higher tender and swollen joint counts.

Conclusion: This study validates the presence of antibody reactivity to novel UH-RA peptides in seronegative and early RA. This might reinforce current diagnostics and improve early diagnosis and intervention in RA.

Keywords: anti-citrullinated protein antibodies; autoantibodies; biomarkers; diagnosis; early disease; rheumatoid arthritis; rheumatoid factor; serological gap; seronegative.