Immunological characteristics of patients with anti-synthetase syndrome overlap with rheumatoid arthritis

Objective: To investigate the clinical and immunological characteristics of anti-synthetase syndrome (ASS) patients overlap with rheumatoid arthritis (RA).

Methods: A retrospective analysis was conducted on ASS patients with arthritis who were treated at Peking University People' s Hospital. Data collected included demographic information, clinical manifestations, laboratory features, lymphocyte subsets in peripheral blood, and treatments. The patients with ASS were divided into two groups based on the presence or absence of RA for comparative analysis.

Results: A total of 104 ASS patients with arthritis were included, among whom 23.1% (24/104) were diagnosed with RA. The ASS with RA group had a significantly higher incidence of rapidly progressive interstitial lung disease (RP-ILD) (41.7% vs. 17.6%, P=0.032), number of tender joints [10 (7, 14) vs. 4 (0, 8), P < 0.001], number of swollen joints [4 (2, 8) vs. 2 (0, 4), P=0.012], and rate of bone erosion (47.8% vs. 2.5%, P < 0.001) compared with the non-RA group. Levels of platelets [(289.57±68.74)×103/μL vs. (247.94±77.04)×103/μL, P=0.022], erythrocyte sedimentation rate (ESR) [43 (19, 59) mm/h vs. 18 (10, 44) mm/h, P=0.019], and C-reactive protein (CRP) [19.20 (4.80, 55.36) mg/L vs. 5.68 (1.10, 14.96) mg/L, P=0.006] were found significantly higher in the ASS with RA group than those in non-RA group. Analysis of immune cells in peripheral blood mononuclear cell (PBMC) showed that significantly decreased proportions of CLA+ Treg cells [(11.12±4.10)% vs. (17.22±8.49)%, P=0.003], B cells [8.56% (4.80%, 11.90%) vs. 14.55% (8.75%, 20.29%), P=0.025], and natural killer (NK) cells [7.56% (4.65%, 13.20%) vs. 13.25% (7.46%, 19.25%), P=0.045] in the overlap group compared with non-RA group. Proportion of Naïve Th cells [(52.66±17.66)% vs. (40.76±14.96)%, P=0.033)] was significantly increased in overlap group compared with non-RA group. Overlap group had lower rate of complete clinical response than non-RA group (16.7% vs. 43.8%, P=0.031).

Conclusions: Among ASS patients with arthritis, those with RA have more severe lung and joint involvement and a lower treatment response rate, highlighting the need for early recognition and aggressive intervention.