IRF4 is Correlated with the Conversion to a Th17-Like Phenotype in Regulatory T Cells from the Malignant Pleural Effusion

BACKGROUND: RORγt(+)Foxp3(+) (Th17-like) Tregs are a plastic Treg subset implicated in immune-related diseases; however, the mechanism of Treg phenotypic transformation in malignant pleural effusion (MPE) has not been elucidated. METHODS: The percentage of CD4(+)CD25(+)Foxp3(+)Helios(+) and RORγt(+)Foxp3(+) Tregs from peripheral blood and pleural effusion mononuclear cells were measured. The level of interferon regulatory factor 4 (IRF4) mRNA expression was detected by quantitative real-time reverse transcription polymerase chain reaction. The effects of IRF4 on the induction of Tregs from patients with non-small cell lung cancer (NSCLC) were evaluated in vitro. Correlation assays between IRF4 expression and the frequency of RORγt(+)Foxp3(+) Tregs were performed. RESULTS: The frequency of CD4(+)CD25(+)Foxp3(+)Helios(+) Tregs and CD4(+)RORγt(+) Th17 cells was both increased in the MPE of NSCLC patients. The group of double-positive Foxp3(+)RORγt(+) Treg phenotype were identified in the pleural effusion. A significant increase in the frequency of Foxp3(+)RORγt(+) Tregs was found in MPE compared with the non-malignant pleural effusion (NPE). Compared to NPE, the relative level of IRF4 expression was increased in the MPE. IRF4 expression was positively associated with the frequency of Foxp3(+)RORγt(+) Tregs in the PE. In vitro, the level of Helios mRNA and protein expression was reduced in induced Tregs following IRF4 over-expression. Additionally, the level of RORγt protein expression was substantially increased. However, ectopic Helios expression in induced Tregs reversed the effects induced by enhanced IRF4 expression. CONCLUSION: IRF4 may serve as a potential molecule that promotes the conversion of regulatory T cells from MPE to a Th17-like phenotype by modulating Helios.