OBJECTIVEAllergic asthma is thought to be mediated by CD4+ T lymphocytes producing the Th2-associated cytokines, which play a critical role in the development of the airway hyper-responsiveness and the eosinophilic inflammatory response. The costimulatory pathway CD28/B7 has been shown to play an important role in CD4+ T cell activation in allergic asthma. This study was conducted to evaluate the role of another costimulatory pathway OX40/OX40 ligand (L) in the pathogenesis of allergic asthma in BALB/c mice.

METHODSAn allergic asthma model in BALB/c mice was established. Thirty-six BALB/c mice were randomly divided into three groups with 12 in each. Mice in treatment group (group B) were treated with neutralizing anti-OX40L monoclonal antibody (mAb, 300 microg per mouse) during the sensitization period. Mice in two control groups, asthma model group (group A) and IgG antibody group (group C) were treated with normal saline (NS) and control IgG respectively instead of anti-OX40L mAb. Bronchoalveolar lavage fluid (BALF) was collected from the mice of each group for counting the total number of white blood cells (including neutrophil granulocyte, lymphocyte, monocyte and eosinophil granulocyte) and the proportions of these cells. The levels of IL-4 and INF-gamma in BALF were measured by ELISA. Lungs were removed for morphological examination after HE and PAS staining, and expression of OX40 in lungs was evaluated by immunohistochemical method.

RESULTS(1) The count of total number of white blood cells in BALF (x10(6)/ml) was lower in group B than that of group A and group C (26.6 +/- 4.6 vs. 36.8 +/- 5.2 and 34.3 +/- 6.9, respectively), the difference between the treatment group (group B) and two control groups (groups A and C) was significant; The proportions of eosinophils and lymphocytes in the BALF (%) were lower in group B than those in group A and group C (eosinophils 15.1 +/- 2.6 vs. 20.0 +/- 4.1 and 19.9 +/- 3.9, respectively; lymphocytes 7.0 +/- 0.9 vs. 8.9 +/- 1.6 and 8.6 +/- 1.8, respectively), the difference between the treatment group and two control groups was significant. (2) The IL-4 level in BALF (pg/ml) was lower in group B than that in group A and group C (672 +/- 58 vs. 809.57 +/- 106.00 and 784 +/- 58, respectively), but the INF-gamma levels in BALF (pg/ml) were higher than those in group A and group C (0.86 +/- 0.09 vs. 0.69 +/- 0.15 and 0.67 +/- 0.13 respectively), and all the differences were statistically significant. (3) The expression of OX40 in the lungs of mice in group B were at a lower level than that of group A and group C, and the morphological changes of asthma were ameliorated in the mice of the treatment group. The signs of mice in treatment group were obviously ameliorated as compared to the two control groups.

CONCLUSIONBlocking the costimulatory pathway by administering the neutralizing anti-OX40L mAb during the sensitization period of allergic asthma model could balance the Th1/Th2 responses, inhibit lung inflammation and ameliorate the signs of mice model of asthma.