IL-4 confers resistance to IL-27–mediated suppression on CD4+ T cells by impairing signal transducer and activator of transcription 1 signaling

Background T H 2 cells play a critical role in the pathogenesis of allergic asthma. Established T H 2 cells have been shown to resist reprogramming into T H 1 cells. The inherent stability of T H 2 cells poses a significant barrier to treating allergic diseases. Objective We sought to understand the mechanisms by which CD4 + T cells from asthmatic patients resist the IL-27–mediated inhibition. Methods We isolated and cultured CD4 + T cells from both healthy subjects and allergic asthmatic patients to test whether IL-27 can inhibit IL-4 production by the cultured CD4 + T cells using ELISA. Culturing conditions that resulted in resistance to IL-27 were determined by using both murine and human CD4 + T-cell culture systems. Signal transducer and activator of transcription (STAT) 1 phosphorylation was analyzed by means of Western blotting and flow cytometry. Suppressor of cytokine signaling ( Socs ) mRNA expression was measured by using quantitative PCR. The small interfering RNA method was used to knockdown the expression of Socs3 mRNA. Results We demonstrated that CD4 + T cells from asthmatic patients resisted the suppression of IL-4 production mediated by IL-27. We observed that repeated exposure to T H 2-inducing conditions rendered healthy human CD4 + T cells resistant to IL-27–mediated inhibition. Using an in vitro murine culture system, we further demonstrated that repeated or higher doses of IL-4 stimulation, but not IL-2 stimulation, upregulated Socs3 mRNA expression and impaired IL-27–induced STAT1 phosphorylation. The knockdown of Socs3 mRNA expression restored IL-27–induced STAT1 phosphorylation and IL-27–mediated inhibition of IL-4 production. Conclusions Our findings demonstrate that differentiated T H 2 cells can resist IL-27–induced reprogramming toward T H 1 cells by downregulating STAT1 phosphorylation and likely explain why the CD4 + T cells of asthmatic patients are resistant to IL-27–mediated inhibition.