Grass pollen immunotherapy inhibits seasonal increases in basophils and eosinophils in the nasal epithelium

Background Symptoms of allergic rhinitis are accompanied by infiltration of the nasal mucosa with inflammatory cells, predominantly eosinophils and me tachromatic cells (basophils and mast cells). Specific immunotherapy (IT) r educes mucosal eosinophilia and numbers of metachromatic cells in the epith elium. A specific marker distinguishing basophils from mast cells was recen tly developed. Objectives The basophil-specific manoclanal antibody 2D7 was used to determ ine the influence of subcutaneous IT on numbers of nasal mucosal basophils compared with the effects of IT on neutrophils, eosinophils and mast cells. Method During a randomized, placebo-controlled trial of grass pollen IT in 44 adults with severe summer hay fever, nasal biopsies were taken at baseli ne, out of the pollen season, and at the peak of the pollen season followin g 2 years treatment. Biopsies were processed for immunohistochemistry far b asophils (2D7(+)), mast cells (AA1(+)), eosinophils (MBP+) and neutrophils (neutrophil elastase(+)). Results In placebo-treated (PL) patients there were significant seasonal in creases in basophils (P<0.01), mast cells (P<0.05) and eosinophils (P=0.002 ) irt the nasal submucosa. In IT-treated patients significant increases in 2D7 cells (P<0.01) and eosinophils (P=0.01) but not AA1(+) cells (P=0.9) we re observed. These differences were significant between groups for eosinoph ils (P<0.05). In the epithelium there were seasonal increases in AA1(+) cel ls and eosinophils in both groups (PL: P<0.01, IT: P<0.05 far both). The be tween-group difference was significant for eosinophils (P=0.05). Basophils were observed in the epithelium of six out of 17 in the placebo group and o ne out of 20 in the IT group (P=0.03). Neutrophil numbers remained constant in both epithelium and submucosa. Conclusion Successful grass pollen immunotherapy was associated with inhibi tion of seasonal increases in basophils and eosinophils, but not mast cells or neutrophils within the nasal epithelium. Immunotherapy may act, at leas t in part, by reducing seasonal recruitment of basophils and eosinophils in to the epithelium.