Decreased Circulating Interleukin-35 Levels Are Related to Interleukin-4-Producing CD8+ T Cells in Patients with Allergic Asthma

Interleukin (IL)-35 is a newly discovered suppressive cytokine and has been shown to alleviate inflammatory and autoimmune diseases. The purpose of this study was to investigate immunomodulatory capacity of IL-35 in patients with allergic asthma. IL-35 mRNA expression levels in peripheral blood mononuclear cells (PBMCs) were detected by quantitative real-time PCR (qPCR). The frequencies of cytotoxic T cells (Tc)1, Tc2 and Tc17 cells were measured by flow cytometry. Plasma levels of IL-35, interferon (IFN)-gamma, IL-4, and IL-17 were examined by enzyme-linked immunosorbent assay (ELISA). The correlations between plasma IL-35 levels and Tc1, Tc2, and Tc17 cytokine production in allergic asthmatics (n = 25) and healthy controls (n = 12) were analyzed by Pearson's test. IL-35 protein and mRNA expression levels were down-regulated in allergic asthmatics compared with healthy controls. The frequencies of Tc2 and Tc17 cells were significantly increased in patients with asthma, and the frequency of Tc1 cells did not differ between asthmatic patients and healthy controls. Similarly, plasma levels of IL-4 and IL-17 were significantly increased in asthmatic patients, while there was no difference in IFN-gamma levels between allergic asthma patients and healthy controls. More importantly, plasma IL-35 protein levels were negatively correlated with the frequency of IL-4-producing CD8(+) T (Tc2) cells and with the IL-4 level in patients with allergic asthma. Our results suggest that decreased circulating IL-35 levels could contribute to the pathogenesis of allergic asthma by regulating CD8(+) T cells.