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 airway s characterized by recruitment of eosinophils into the epithelial layer, ch ronic 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 inflamm ation is unknown. Methods We used a chronic inhalational exposure model of asthma in ovalbumi n-sensitized BALB/c mice to examine the phenotype of immunoglobulin-secreti ng cells and mast cells in the airway wall. In parallel, we assayed ovalbum in-specific IgG and total IgE in the plasma of these animals. Results In sensitized mice exposed to aerosolized ovalbumin for 6 weeks, ag gregates of chronic inflammatory cells consisted of a majority of plasmacyt oid cells, including numerous IgG-synthesizing cells, which were significan tly increased in sensitized animals compared to controls. IgA-synthesizing cells were also present, but were not increased in the sensitized exposed m ice. Immunoglobulins in the cytoplasm of the plasma cells were demonstrated to be antigen-specific. No IgM-or IgE-synthesizing cells were observed, al though levels of total IgE in the plasma were significantly increased. Ther e 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 inf lammation in the airway wall is consistent with development of a local IgG- mediated humoral immune response. However, there is no evidence of local pr oduction of IgE or recruitment of mast cells.