OBJECTIVETo investigate the effects of low-concentration ozone exposure on the percentage of CD4(+)CD25(high)Foxp(3+) regulatory T cells and the mRNA expression of transcription factor Foxp3 in asthmatic rats.

METHODSSixty male Wistar rats were randomly divided into 4 groups (n = 15 for each): normal control group, ovalbumin (OVA) exposure group, ozone exposure group, and OVA+ozone exposure group. The OVA exposure group was sensitized and challenged with OVA to establish an asthma model; the normal control group inhaled aerosolized saline; the ozone exposure group inhaled low-concentration ozone; the OVA+ozone exposure group inhaled low-concentration ozone before being challenged with aerosolized OVA every day. The percentage of CD4(+)CD25(high)Foxp(3+) regulatory T cells in CD4(+) T cells was determined by flow cytometry. The levels of interferon-γ (INF-γ) and interleukin 4 (IL-4) in peripheral blood and lung tissue were measured by enzyme-linked immunosorbent assay. The mRNA expression of Foxp3 in lung tissue was measured by PCR.

RESULTSThe percentages of CD4(+)CD25(high)Foxp(3+) regulatory T cells in OVA exposure group (6.12±1.03%) and ozone exposure group (5.87±1.26%) were significantly lower than that in normal control group (9.85±1.34%), and the percentage of CD4(+)CD25(high)Foxp(3+) regulatory T cells in OVA+ozone exposure group (3.31±0.85%) was significantly lower than those in normal control group and OVA exposure group (P < 0.01). The levels of IL-4 in plasma and lung tissue in OVA exposure group (plasma: 21.83±5.12 ng/L; lung tissue: 0.89±0.13 ng/L) were significantly higher than those in normal control group (plasma: 10.58±2.73 ng/L; lung tissue: 0.32±0.11 ng/L) (P < 0.01). The levels of IL-4 in plasma and lung tissue in OVA+ozone exposure group (plasma: 35.47±7.24 ng/L; lung tissue: 1.50±0.42 ng/L) were significantly higher than those in normal control group and OVA exposure group (P < 0.01). The levels of INF-γ in plasma and lung tissue in OVA exposure group (plasma: 61.78±23.45 ng/L; lung tissue: 0.69±0.21 ng/L] were significantly lower than those in normal control group [plasma: 158.89±60.23 ng/L; lung tissue: 1.86±0.29) (P < 0.01). The levels of INF-γ in plasma and lung tissue in OVA+ozone exposure group (plasma: 10.28±2.63 ng/L; lung tissue: 0.41±0.12 ng/L) were significantly lower than those in normal control group and OVA exposure group (P < 0.01). The mRNA expression of Foxp3 was significantly lower in the OVA+ ozone exposure group than in the normal control group (P < 0.05).

CONCLUSIONLow-concentration ozone exposure may decrease the number of CD4(+)CD25(high)Foxp(3+) regulatory T cells and inhibit the mRNA expression of Foxp3 to promote Th1/Th2 imbalance in asthmatic rats, suggesting that ozone exposure may be one of factors that induce asthma attack.