[Pathogenic mechanism of CD8(+)CD28(-)T cell and the effect of dexamethasone in asthmatic mouse]

To explore whether or not CD8(+)CD28(-)T cell play a pathogenic role in asthma and detect the effects of dexamethasone (DXM).

A total of 30 mice were randomly divided into 3 groups: asthmatic group, DXM group and control group (n = 10 each). The asthmatic and DXM groups were sensitized twice and inhaled ovalbumin. The DXM Group received an intraperitoneal injection of DXM 1mg/kg before inhaling ovalbumin. After successful modeling, 3 mice were selected randomly from each group to measure the airway responsiveness. Also a bronchoalveolar lavage cytological study was performed and lung tissue sections were prepared for histopathologic examination to evaluate the airway inflammation. The content of IgE in bronchoalveolar lavage fluid (BALF) was detected with a murine IgE ELISA kit. And the fractions of CD8(+)CD28(-)T cell of peripheral blood and BALF were tested by flow cytometry to analyze the correlation between IgE, eosinophils (EOS) of BALF and CD8(+)CD28(-)T cell of blood.

The airway hyperresponsiveness in asthmatic and DXM groups were significantly higher than that in the control group. The number of total cells and EOS of BALF in the asthmatic group [(5.56 ± 4.06) × 10(2)/L; (3.29 ± 2.23) × 10(2)/L] were significantly higher than that in control group [(0.91 ± 0.65) × 10(2)/L, P = 0.003; (0.43 ± 0.37) × 10(2)/L, P = 0.001] and DXM group [(2.59 ± 1.69) × 10(2)/L, P = 0.044; (1.11 ± 0.73) × 10(2)/L, P = 0.008]; while the DXM group was insignificantly higher than the control group (P = 0.234, P = 0.363). There were significant differences in the contents of IgE of BALF for the asthmatic, DXM and control groups [(23.85 ± 5.97) g/L, (13.15 ± 2.22) g/L, (6.54 ± 1.03) g/L, F = 38.558, P = 0.000]. The percentages of CD8(+)CD28(-)T cell in peripheral blood in asthmatic and DXM groups [(18.68 ± 4.12)% and (13.43 ± 2.91)%] were significantly higher than those in control mice [(8.43 ± 4.60)%, both P < 0.05]. The percentages of CD8(+)CD28(-)T cell of BALF in asthmatic group and DXM group [(1.25 ± 0.40)% and (0.66 ± 0.49)%] were also significantly higher than those in control mice [(0.21 ± 0.19)%, both P < 0.05]. The percentages of CD8(+)CD28(-)T cell of blood and BALF in the DXM mice were significantly lower than those in asthmatic group. The correlations between IgE (r = 0.864, P = 0.012), EOS (r = 0.804, P = 0.029) and CD8(+)CD28(-)T cell were significant.

The fraction of CD8(+)CD28(-)T cell is closely correlated with the inflammation of asthmatic airway. The airway hyperresponsiveness and inflammation in asthmatic mice may be relieved by DXM through its effect of inhibiting the expression of CD8(+)CD28(-) T cell.