Objective: To explore the impact of Foxp3 expression and CD(4)(+)CD(25)(+) regulatory T cells on pathogenesis of childhood asthma.
Methods: Totally 15 patients with acute asthma exacerbation, 15 children with asthma remission and 10 children who were hospitalized for skeleton deformity without atopic disorders or history of allergic diseases or respiratory infections within a month as controls were recruited in this study from Sep. 2004 to Mar. 2005. The percentage of CD(4)(+)CD(25)(+) T cells were detected by 2-color flow cytometry. The levels of interleukin (IL)-4, IL-10, interferon (IFN)-gamma, transforming growth factor (TGF)-beta in plasma and supernatant were assayed by ELISA. Both the asthmatic children and the control children were selected to induce sputum by hypertonic saline. Sputum was processed for detecting the expression of Foxp3-mRNA. The expression of Foxp3-mRNA in both sputum and PBMC was detected by semi-quantitative RT-PCR with beta-actin as internal control.
Results: The percentage of CD(4)(+)CD(25)(+) regulatory T cells in exacerbation and remission asthmatic children was significantly lower than that of the control children both prestimulation [(10.1 +/- 2.1)% vs. (15.5 +/- 2.7)%, (11.7 +/- 2.5)% vs. (15.5 +/- 2.7)%, P < 0.05] and poststimulation with PHA [(12.4 +/- 2.3)% vs. (26.9 +/- 3.8)%, (17.3 +/- 3.2)% vs. (26.9 +/- 3.8)%, P < 0.05]. The percentage of CD(4)(+)CD(25)(+) regulatory T cells was significantly higher after PHA stimulation in normal children [(15.5 +/- 2.7)% vs. (26.9 +/- 3.8)%, P < 0.01]. The expression of Foxp3-mRNA (Foxp3/beta-actin) in asthmatic children was significantly lower than that in the control children in both PBMC and induced sputum. The expression of Foxp3-mRNA in PBMC was significantly higher after PHA stimulation in the control children (0.77 +/- 0.22 vs. 1.07 +/- 0.21, P < 0.05). However, there was no significant difference in Foxp3-mRNA expression in asthmatic children pre and post PHA stimulation. A significant positive correlation between the Foxp3-mRNA expression and the percentage of CD(4)(+)CD(25)(+) regulatory T cells was detected. The levels of IFN-gamma and TGF-beta were significantly lower in asthmatic children than those in the control children, and the levels of IFN-gamma and TGF-beta correlated positively with Foxp3-mRNA expression and the percentage of CD(4)(+)CD(25)(+) regulatory T cells. The level of IL-4 both in plasma and supernatant was higher in asthmatic children. The levels of IL-10 was higher only in exacerbation than in control children, the levels of IL-4 and IL-10 had no correlation with Foxp3-mRNA expression and the percentage of CD(4)(+)CD(25)(+) regulatory T cells.
Conclusion: Insufficient secretion of TGF-beta, decreased Foxp3 expression, insufficient number of CD(4)(+)CD(25)(+) regulatory T cells and the defective ability of converting CD(4)(+)CD(25)(-) T cells to CD(4)(+)CD(25)(+) regulatory T cells might play an important role in pathogenesis of asthma.