Serum Interleukin 35 Levels in Systemic Sclerosis and Relationship With Clinical Features

Interleukin (IL) 35 is a member of the IL-12 family. Studies show that IL-35 is an important anti-inflammatory cytokine and suppresses effector T-cell activity. In this study, we aimed to evaluate serum IL-35 levels in systemic sclerosis (SSc) patients and its potential relation with clinical findings.

We conducted a cross-sectional analysis of 70 SSc patients and 29 healthy volunteers in a single center in 5 months' period. Extension of skin fibrosis was evaluated by using modified Rodnan skin score. Disease severity was assessed by Medsger disease severity scores. Serum IL-35 was measured using a commercial enzyme-linked immunosorbent assay (ELISA) kit (Cloud-Clone Corp, Wuhan, China). The relationship between IL-35 levels and clinical and laboratory parameters was investigated. Mann-Whitney U test was used to compare parameters among the groups. Correlation was tested by Spearsman correlation coefficient.

Serum IL-35 levels was significantly higher in SSc patients (8.69 [interquartile range, 29.33] pg/mL) than in healthy controls (7.11 [interquartile range 7.53] pg/mL; p < 0.001). There was no significant relationship between serum IL-35 levels and organ involvement. There was a negative correlation between serum IL-35 levels and Medsger disease severity score (Rho, -0.333; p = 0.006), modified Rodnan skin score (Rho, -0.307; p = 0.010), and C-reactive protein (Rho, -0.294; p = 0.015). There was no relationship between IL-35 and disease duration and erythrocyte sedimentation rate.

Our study revealed that IL-35 levels were higher in SSc patients, and in contrast to previous studies, it was the first study that showed that IL-35 levels did not increase in SSc patients with pulmonary fibrosis.