Resistance to steroid therapy in a short-term murine model of allergic airway inflammation

Magda Serra, Edna Anjos-Valotta, Patricia Jurgilas, Patricia Silva, Marco Martins. Oswaldo Cruz Foundation, Rio de Janeiro, RJ, Brazil.

Prior studies revealed an increased eosinophilic inflammation and airway hyperrespnsiveness (AHR) after repeated allergen instillation into the nose of A/J mice, whereas these responses progressively reduced in 3 other mouse strains. Because of this unique sensitiveness of A/J mice, these animals were used here to assess the efficacy of glucocorticoid (GC) treatment on the progression of the inflammatory response in a short-term murine model of asthma. Mice of strain A/J were subcutaneously sensitized on days 0 and 14 by a mixture of Al(OH)3 and ovalbumin (OVA), and challenged for 2 or 4 consecutive days starting at day 19 post-sensitization. The animals were subjected to treatment with dexamethasone (DEX, 3 mg/kg, oral), or vehicle, 1 h before each provocation. Invasive and non-invasive pletismography were employed for measurement of AHR. Peribronchial eosinophil infiltration and subepithelial airway fibrosis were analyzed 24 h post-challenge by histomorphometry. Eotaxin, IL-4, IL-5 and IL-13 were quantified in the lung tissue by ELISA as markers of the inflammatory status. Western blotting was used to investigate activation of GATA-3. We found that the two-provocation regimen was active in causing AHR, eosinophilic inflammation, mucus production and fibrogenesis, all of which being clearly sensitive to DEX. As expected, these changes were intensified in those animals subjected to four allergen provocations. DEX remained active in preventing the eosinophil accumulation of BAL fluid samples but failed to alter tissue eosinophilia. Similarly, AHR, increased generation of IL-4, IL-13, eotaxin and fibrogenesis also appeared sensitive to DEX in case of two but not four OVA provocations. We also demonstrated that DEX inhibited GATA-3 expression in the lung tissue following 2 but not 4 consecutive OVA provocations. These findings show that A/J mice develop asthma-like pathological changes that become resistant to the steroid treatment as these changes are progressively exacerbated by the successive allergen provocations. Since, in parallel, the expression of GATA-3 in the lung also appeared increased and less sensitive to DEX, it is not unlikely that an overexpression of GATA-3 may contribute to the state of GC refractoriness seen in this model.

Financial support: FAPERJ, CNPq and PRONEX.