The CD27–CD70 pathway contributes to lymphocyte activation and B–T cell interactions in rheumatoid arthritis (RA). CD27 is a marker of memory B cells, and soluble CD27 has been linked to RA disease activity. Circulating anti-CD27 antibodies may reflect immune dysregulation in RA. 

Serum levels of anti-CD27 antibodies were measured by enzyme-linked immunosorbent assay in 97 RA patients and 24 healthy controls (HC). RA patients were stratified into early RA (disease duration ≤24 months; n=24) and established RA (>24 months; n=73). Disease activity was assessed using the 28-joint Disease Activity Score based on erythrocyte sedimentation rate (DAS28-ESR) and categorized as remission (DAS28-ESR < 2.6), low-to-moderate activity (2.6–5.1) and high activity (>5.1). Group comparisons were performed using non-parametric tests (Mann–Whitney U test for two groups and Kruskal–Wallis test with post hoc Dunn’s multiple comparisons for three or more groups). Associations between anti-CD27 antibody levels and clinical parameters were analyzed using Spearman correlation. In a paired cohort (n=28) with baseline and follow-up samples after treatment, changes (Δ) in anti-CD27 antibody levels and DAS28-ESR were calculated as follow-up minus baseline. Patients were classified as Improved (ΔDAS28-ESR < 0) or Worsened (ΔDAS28-ESR > 0) groups for within-patient comparisons.

Serum anti-CD27 antibody levels were significantly elevated in both early RA and established RA compared with HC (p<0.01 and p<0.001, respectively) (Figure 1A). Anti-CD27 antibody levels were higher in patients with active RA than in HC and patients in remission, with a stepwise increase across activity categories. There was no significant difference in anti-CD27 levels between remission group and HC (Figure 1B). Anti-CD27 antibody levels correlated positively with DAS28-ESR as well as anti-cyclic citrullinated peptide antibodies (anti-CCP), and rheumatoid factor (RF) (p<0.01) (Figure 1C). In paired samples (n=28), Δanti-CD27 antibody levels correlated positively with ΔDAS28-ESR (Spearman's ρ = 0.494, p = 0.008) (Figure 2A). Anti-CD27 antibody levels decreased from baseline to follow-up in the Improved group (paired t-test, p=0.004), whereas a non-significant increase was observed in the Worsened group (p=0.09) (Figure 2B).

Serum anti-CD27 antibody levels were associated with RA disease activity and showed concordant within-patient changes with DAS28-ESR after treatment. These findings support further evaluation of anti-CD27 antibodies as an activity-associated serological measure in RA.