Dermatophagoides-farinae-Induced Pulmonary Eosinophilic Inflammation in Mice

Dermatophagoides farinae (Der f) is one of the most common species of dust mites that induce asthma and allergic rhinitis. We have reported that Der f challenge on sensitized mice elicited a distinct type of hypersensitivity, called early-type hypersensitivity (ETH), in infcutaneous tissues and in airways. The airway ETH was accompanied by a series of inflammatory and immunological events including cytokine production, adhesion molecule expression, inflammatory cell infiltration, eosinophilia, and airway hyperreactivity. In the present study, we further defined the course of the Der-f-induced eosinophilia and examined the local cytokine gene expression and the roles of cytokines, mast-cell-derived vasoactive amines, and corticosteroids in the development of pulmonary eosinophilia. BALB/c mice were sensitized with crude extract of Der f in complete Freund’s adjuvant and were intranasally challenged with Der f on day 14 after sensitization. The number of blood eosinophils, total and differential leukocyte counts in bronchoalveolar lavage (BAL) fluids, and the expression of cytokine genes in BAL cells were assessed at various time points after challenge for up to 12 days. The total number of leukocytes in the BAL fluids was increased 6 h after challenge (AC) and peaked at 72 h. The early cellular response in the BAL fluids was dominated by neutrophils which were infsequently replaced by a marked infiltration of eosinophils. The number of eosinophils in BAL fluids increased at 24 h and peaked at 72 h, making up 43% of all cells recovered by BAL. BAL eosinophils declined gradually to normal background levels around day 12. Concurrently, there was a significant reduction in the number of eosinophils in blood 24 h AC. The number of blood eosinophils increased thereafter, reached a peak at 72 h, and remained above baseline level for up to 10 days. Saline challenge did not induce eosinophilia in BAL fluids and blood of sensitized mice. Histopathological examination revealed a mixed granulocytic, monocytic pulmonary inflammation with a large number of eosinophils accumulating within the infmucosa of the airways and blood vessels of sensitized mice after challenge. Der f challenge induced a sequential expression pattern of eight cytokine genes in BAL cells. The mRNA of interleukin (IL)-1β and tumor necrosis factor (TNF)-α strongly expressed throughout the course of the experiment. The IL-6 mRNA expression peaked at 0.5-72 h, IL-10 at 1-6 and 48-72 h, IL-4 at 6-72 h, IL-2 at 6-96 h, IL-5 at 24-72 h, and interferon-γ at 24-96 h. Intraperitoneal injection of sensitized mice with monoclonal antibody (mAb) to murine IL-5 (TRFK5, 300 μg/mouse) 1 h before challenge caused 62% suppression of eosinophils in the BAL fluids. The concomitant accumulation of neutrophils and mononuclear cells, however, was not affected by this treatment. On the other hand, intranasal administration of mAb to murine TNF-α (MP6-XT3,20 μg/ mouse), but not IL-5, 1 h before challenge and 24 h AC significantly reduced the numbers of eosinophils, neutrophils, and lymphocytes in the BAL fluids. The intraperitoneal injection of dexamethasone (50 mg/kg) for a total of four times resulted in total inhibition of the Der-f-induced cellular responses, whereas vasoactive amine antagonists (diphenhydramine, ketanserin and cyprohepatidine) did not show any effect.