Airway inflammation in a murine model of chronic asthma: Evidence for a local humoral immune response

Background: Asthma is an acute-on-chronic inflammatory disease of the airways characterized by recruitment of eosinophils into the epithelial layer, chronic inflammation in the lamina propria, as well as variable accumulation of mast cells in the airway wall. The role of local production of allergen-specific immunoglobulins in triggering mast cell-mediated asthmatic inflammation is unknown. Methods: We used a chronic inhalational exposure model of asthma in ovalbuminsensitized BALB/c mice to examine the phenotype of immunoglobulin-secreting cells and mast cells in the airway wall. In parallel, we assayed ovalbumin-specific IgG and total IgE in the plasma of these animals. Results: In sensitized mice exposed to aerosolized ovalbumin for 6 weeks, aggregates of chronic inflammatory cells consisted of a majority of plasmacytoid cells, including numerous IgG-synthesizing cells, which were significantly increased in sensitized animals compared to controls. IgA-synthesizing cells were also present, but were not increased in the sensitized exposed mice. Immunoglobulins in the cytoplasm of the plasma cells were demonstrated to be antigen-specific. No IgM-or IgE-synthesizing cells were observed, although levels of total IgE in the plasma were significantly increased. There was no recruitment of mast cells of either the mucosal or the connective tissue phenotype into the lamina propria or the epithelium. Conclusion: In this experimental model of chronic asthma, the pattern of inflammation in the airway wall is consistent with development of a local IgG-mediated humoral immune response. However, there is no evidence of local production of IgE or recruitment of mast cells.