Objective:To establish a real-time fluorescent quantitative reverse transcription polymerase chain reaction(RT-PCR)to detect FOXP3 mRNA expression in human peripheral blood mononuclear cells(PBMCs)and to investigate the correlations between activity of CD4+CD25+ regulatory T cells and expression of FOXP3 mRNA.Methods:Total RNA was extracted with Trizol from human PBMCs and mRNA was transcribed reversely into cDNA.Real-time fluorescent quantitative RT-PCR with β-actin as the internal control gene was used to detect the expression levels of FOXP3 mRNA in 29 pediatric patients with asthma and 24 age-matched healthy children.The specificity of PCR productions was identified with the dissociation curves and agarose gel electrophoresis.Flow cytometry analysis was used to assess the percentage of CD4+CD25+regulatory T cells.The correlation between the expression and activity was analyzed.Results:The percentages of CD4+CD25+ regulatory T cells in group of asthma were significantly lower than those in group of control(P0.01),so did the expressions of FOXP3 mRNA(P0.05).The analysis of dissociation curves on FOXP3 and β-actin showed that both of them had only one simple spike and the Tm values were 82.4 ℃ and 87.8 ℃,respectively.The agarose gel electrophoresis of them showed only single PCR product each.Conclusion:It is an easy and reliable test to detect the expression level of FOXP3 mRNA by SYBR GreenⅠreal-time fluorescence quantitative RT-PCR and the preliminary experimental result shows that the percentages of CD4+CD25+ regulatory T cells and the expressions of FOXP3 mRNA have the same trend and confirms the correlation between them.