Demographic data of enrolled RA patient
The study included 116 RA patients and 27 healthy controls. The demographics and clinical characteristics of the RA patients are shown in Table 1. Among 116 patients with RA, 83 (71.6%) were female and their mean age was 63.5 years. The majority of the RA patients were taking disease-modifying anti-rheumatic drugs (DMARDs), mostly methotrexate (59/116 50.9%), and biologics (38/116 32.8%).
Serum sTIM-3 Concentrations In RA Patients
Serum sTIM-3 levels were significantly higher in RA patients than they were in the healthy subjects (Fig. 1). There were significant positive correlations between serum sTIM-3 and rheumatoid inflammatory markers such as erythrocyte sedimentation rate (ESR, r = 0.27, p = 0.004), matrix metalloproteinase-3 (MMP-3, r = 0.35, p < 0.001), and ACPA titers (r = 0.27 p = 0.005).
Relationships Between sTIM-3 And ACPA Titers
To further evaluate the capacity of serum sTIM-3 to differentiate between RA phenotypes, distribution patterns of serum sTIM-3values were analyzed in conjunction with anti-citrullinated peptide antibody (ACPA) titers. In a two-dimensional map consisting of serum sTIM-3 and ACPA titer, two distinct groups were apparent (Fig. 2). The cut-off values of ACPA titers (200 U/ml) was determined according to the ability to discriminate the differential correlations between sTIM-3 and ACPA titer. There was a significant modest correlation between sTIM-3 and ACPA titer in RA patients with high ACPA titers (≥ 200 U/mL r = 0.508, p = 0.002). Whereas, there was no correlation between sTIM-3 and ACPA titer in RA patients with low ACPA titers (< 200 U/mL). There was differential correlations between serum sTIM-3 levels and ACPA titers in these two groups, suggesting that sTIM-3 could be modulated by ACPA titers.
Relationships between sTIM-3 and clinical and laboratory parameters (Fig. 3)
In RA patients with low ACPA titers (< 200 U/mL), serum sTIM-3 was significantly correlated with the inflammatory markers, ESR (r = 0.36, p = 0.001) and MMP-3 (r = 0.38, p < 0.001). Whereas corresponding correlations were not significant in RA patients with high ACPA titers (≥ 200 U/mL). These findings suggest that serum sTIM-3 upregulation may be associated with autoimmune responses in RA patients with high ACPA titers, whereas serum sTIM-3 was upregulated in response to inflammatory mediators in RA patients with low ACPA titers.
In RA patients with low ACPA titers (< 200 U/mL), circulating sTIM-3 was significantly higher in CRP-positive patients than it was in CRP-negative patients (2871 pg/mL, [IQR 2145–3921] versus. 2081 pg/mL, [IQR 1714–2840], p = 0.007). Conversely, in patients with high ACPA titers (≥ 200 U/mL) there was no significant difference in circulating sTIM-3 between CRPpositive and CRP-negative patients (2998 pg/mL, [IQR 2640–3960] versus. 2385 pg/mL, [IQR 1712–3826], p = 0.20).
Relationships Between sTIM-3 And RA Clinical Outcomes
From a clinical point of view, the circulating sTIM-3 were compared according to the presence or absence of clinical remission in RA patients (Fig. 4A). Serum sTIM-3 was significantly higher in RA patients without clinical remission compared to those with clinical remission (2852 pg/ml [IQR: 2013–3584] versus 1954 pg/ml [IQR: 1611–2875], p = 0.005). As shown in Fig. 4B, RA patients with advanced joint damage (stage III or IV) had significantly higher levels of serum sTIM-3 than those without advanced joint damage (2830 pg/ml [IQR: 2181–4047] versus 2428 pg/ml [IQR: 1927–3175], p = 0.011). There was a differential relationship between circulating sTIM-3 and rheumatoid inflammatory markers in the presence or absence of advanced joint damage (stage III or IV). In RA patients with advanced joint damage (stage III or IV), serum sTIM-3 significantly correlated with MMP-3 but not with ESR. Conversely, in RA patients without advanced joint damage, circulating sTIM-3 was significantly correlated with ESR, whereas there was a weak correlation between sTIM-3 and MMP-3 (Fig. 5).