Grass pollen immunotherapy: Symptomatic improvement correlates with reductions in eosinophils and IL-5 mRNA expression in the nasal mucosa during thepollen season

Background: Tissue eosinophilia and infiltration by T(H)2-type T tells are characteristic features of allergic rhinitis both after allergen challenge and during natural allergen exposure. Specific immunotherapy inhibits aller gen-induced nasal eosinophilia. Objectives: We sought to assess, in the context of a randomized trial, the relationships between symptomatic improvement after immunotherapy and eosin ophil numbers and IL-5 expression in the nasal mucosa during the pollen sea son. Methods: Nasal biopsy specimens were taken from 37 adults with severe summer hay fever at baseline (out of season) and at peak season after 2 yea rs of treatment with a depot grass pollen extract or placebo. Biopsy specim ens were processed for immunohistochemistry by using mAbs against eosinophi ls (EG2), T cells (CD3), and IL-2 receptor-positive cells (CD25), as well a s for in situ hybridization by using a sulfur 35-labeled antisense riboprob e directed against IL-5. Results: Immunotherapy significantly reduced symptoms (49%, P = .01) and me dication requirements (80%, P = .007) compared with placebo. There was a 40 0% increase (P = .004) in eosinophils during the pollen season in placebo-t reated patients, which was inhibited in the immunotherapy group (20% increa se, P = .04 between groups). Seasonal increases were also observed for CD25 (+) cells (P = .002), CD3(+) cells (P = .02), and IL-5 mRNA-expressing cell s (P = .03) in the placebo group but not in the immunotherapy group. A sign ificant correlation was observed between eosinophils and IL-5 expression (r = 0.5, P < .05). Both eosinophils (r = 0.6, P < .02) and IL-5 (r = 0.6, P < .02) correlated with symptoms after immunotherapy. Conclusion: Improvemen t in symptoms after grass pollen immunotherapy may result, at least in part , from inhibition of IL-5-dependent tissue eosinophilia during the pollen s eason. Conclusion: Improvement in symptoms after grass pollen immunotherapy may re sult, at least in part, from inhibition of IL-5-dependent tissue eosinophil ia during the pollen season.