Th2 cells play a critical role in the pathogenesis of allergic asthma. Established Th2 cells have been shown to resist reprogramming into Th1 cells. The inherent stability of Th2 cells poses a significant barrier to treating allergic diseases.
We sought to understand the mechanisms by which CD4+ T cells from asthmatic patients resist the IL-27-mediated inhibition.
We isolated and cultured CD4+ T cells from both healthy individuals and allergic asthmatic patients in order 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 using both murine and human CD4+ T cell culture systems. STAT1 phosphorylation was analyzed by Western blot and flow cytometry. Suppressor of cytokine signaling (Socs) mRNA expression was measured by quantitative PCR. The small interfering RNA method was used to knockdown the expression of Socs3 mRNA.
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 Th2-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.
Our findings demonstrate that differentiated Th2 cells can resist IL-27-induced reprogramming toward Th1 cells by downregulating STAT1 phosphorylation and likely explain why the CD4+ T cells of asthmatic patients are resistant to IL-27-mediated inhibition.