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Rush immunotherapy (RIT) has been shown to be effective in allergic asthma.We investigated the mechanisms of RIT on the basis of cytokine production by T-cell lines and airway inflammation and responsiveness.Subjects were 8 patients with house dust mite-allergic asthma treated with dust mite extract RIT for 6 months and 6 RIT-untreated control patients. IL-5 production by Dermatophagoides farinae -specific T-cell lines, eosinophil percentages, and eosinophil cationic protein (ECP) in induced sputum and airway responsiveness to allergen and histamine were evaluated before and after treatment. Changes in eosinophil percentages and ECP in induced sputum and responsiveness to histamine 24 hours after allergen inhalation were also studied.After 6 months of RIT, percentages of total eosinophils (43. 0% +/- 6.90% to 16.8% +/- 2.48%; P.01), percentages of EG2(+ ) eosinophils (32.6% +/- 6.39% to 19.7% +/- 4.68%; P.01) and ECP (362.7 +/- 125.3 ng/mL to 26.2 +/- 5.15 ng/mL; P.05) decreased in induced sputum, and IL-5 production by T-cell lines decreased (617 +/- 93.2 pg/mL to 200.0 +/- 34.1 pg/mL; P.01). RIT decreased both early- and late-phase bronchoconstriction (early phase: 33.2% +/- 3. 46% to 25.4% +/- 1.42%; P.03; late phase: 16.2% +/- 3.52% to 6.2% +/- 1.96%; P.03) and suppressed increases in the percentages of total (61.8% +/- 4.89% to 42.0% +/- 4.67%; P.01) and EG2-positive eosinophils (55.54% +/- 7.21% to 36.5% +/- 6.43%; P.01) and ECP (685.6 +/- 217.0 ng/mL to 85.4 +/- 23.4 ng/mL; P.05) in induced sputum after allergen inhalation. RIT also decreased airway responsiveness to dust mite (1:303.7 +/- 123.7 wt/vol to 1:65.0 +/- 13.2 wt/vol; P.03) and to histamine before (397.1 +/- 206.9 microgra/mL to 1391.3 +/- 283.3 microgram/mL; P.03) and after allergen inhalation (139.2 +/- 36.5 microgram/mL to 629.1 +/- 196.3 microgram/mL; P.03).RIT decreases airway inflammation and airway hyperresponsiveness before and after bronchial provocation with allergen, possibly by inhibiting both allergen-specific T-cell- and mast cell-dependent pathways. RIT is an effective antiinflammatory treatment in allergic asthma.