Patients with ACPA-positive and ACPA-negative Rheumatoid Arthritis Show Different Serological Autoantibody Repertoires and Autoantibody Associations with Disease Activity

Abstract

Objectives. Patients with rheumatoid arthritis (RA) can test either positive or negative for anti-citrullinated protein antibodies (ACPA), and are thereby ACPA-positive (ACPA+) or ACPA-negative (ACPA-), respectively. Through comprehensive profiling of autoantibodies in serum, we aimed to identify autoantibodies that are differentially abundant between patients with ACPA+ RA and ACPA- RA, and also those that are significantly associated with clinical disease activity. Methods. Serum was collected from patients with ACPA+ RA (n = 32), ACPA- RA (n = 30), and healthy controls (n = 30). Sengenics Immunome™ protein microarray was used to screen for over 1,600 IgG autoantibodies against native, unmodified human proteins from each serum sample. Autoantibody profiles were compared between each RA subgroup and controls to identify differentially abundant autoantibodies (P < 0.05, Mann-Whitney U test; |Cliff′s delta (d)| > 0.33). Additionally, the relationship between RA patients′ autoantibody abundances and Clinical Disease Activity Index (CDAI) was examined for correlations between serum autoantibodies and disease activity (|Spearman′s ρ| > 0.4 and P < 0.01). Results. We identified differences in serum autoantibodies between patients with ACPA+ RA and ACPA- RA compared with healthy controls. Specifically, we found 22 and 19 autoantibodies higher in ACPA+ RA patients and ACPA- RA patients, respectively. Among these two sets of autoantibodies, only one autoantibody (anti-GTF2A2) was common in both comparisons. On the other hand, we found 30 and 25 autoantibodies lower in ACPA+ RA and ACPA- RA, respectively, of which eight autoantibodies were common in both comparisons. Functional enrichment analysis of the protein antigens targeted by these autoantibodies showed an over-representation of a range of essential biological processes, including programmed cell death, metabolism, and signal transduction. Lastly, we found that autoantibodies correlate with CDAI, but associate differently depending on the presence or absence of ACPA. Conclusions. ACPA status in patients with RA determines not only the composition of the serum autoantibody repertoire, but also the correlative relationships between autoantibodies and disease activity. Notably, many of the autoantibodies identified herein were reported for the first time. Our findings warrant further investigation into the immunological differences between these two RA subgroups, and shed new light on the possible need for different treatment approaches.