['Interleukin-37 (IL-37) has been known to play an immunosuppressive role in various inflammatory disorders, but whether it participates in the regulation of pathogenesis of ankylosing spondylitis (AS) has not been investigated. Here, we examined the serum levels of IL-37 and its clinical association in AS, and explored the anti-inflammatory effects of IL-37 on peripheral blood mononuclear cells (PBMCs) from AS patients.', 'The mRNA levels of IL-37, TNF-α, IL-6, IL-17, and IL-23 in PBMCs and their serum concentrations from 46 AS patients were examined by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunoassay (ELISA), respectively. The correlations between serum IL-37 levels with disease activity, laboratory values and pro-inflammatory cytokines in AS were analyzed by Spearman correlation test. PBMCs from 46 AS patients were stimulated with recombinant IL-37 protein, expressions of TNF-α, IL-6, IL-17 and IL-23 were determined by RT-PCR and ELISA.', 'Compared to healthy controls (HC), AS patients and active AS patients showed higher levels of IL-37 in PBMCs and serum respectively. Strikingly, serum IL-37 levels were higher in AS patients with osteoporosis than those without. Serum levels of IL-37 were correlated with laboratory values as well as TNF-α, IL-6 and IL-17, but not IL-23 in patients with AS. The productions of pro-inflammatory cytokines such as TNF-α, IL-6, IL-17, IL-23 in PBMCs from AS patients were obviously attenuated after recombinant IL-37 stimulation, but not in the HC.'] Is interleukin-37 increased in ankylosing spondylitis patients and associated with disease activity?