Immunohistology and in situ hybridization were used to evaluate the presence, activation status, and cytokine mRNA profile of cells in the bronchial mucosa during human allergen-induced asthma. Fifteen atopic asthmatic subjects underwent inhalation challenge with allergen and with allergen diluent, performed in random order separated by an interval of at least 3 wk. Bronchial biopsies were obtained 24 h after challenge. Immunostaining revealed increases in the numbers of secreting eosinophils (EG2+; P< O. OS) and in interleukin-2 receptor (IL-2R)-positive cells (CD2S+; P< 0.01) after allergen compared with diluent challenge. No differences were observed in the numbers of total leukocytes (CD4S+), T lymphocytes (CD3+, CD4", and CD8+), elastase-positive neutrophils, macrophages (CD68+), or mast cell subtypes (MCT+ or MCTc"). In situ hybridization revealed significant increases in the numbers of cells expressing mRNA for IL-S (P< 0.02) and granulocyte/macrophage colony-stimulating factor (P< 0.01) after allergen compared with diluent challenge. A significant inverse relationship was observed between the number of cells expressing mRNA for IL-4 and for interferon-v (r=-0.7 S, P< 0.02). The results support the view that cytokines possibly from activated T lymphocytes may contribute to local eosinophil accumulation during allergen-induced asthma.

Allergen-induced late-phase responses are accompanied by increases in peripheral blood mediator concentrations (1-4), changes in blood eosinophils (S-8), and bronchoalveolar eosinophilia (9-12). Eosinophils may contribute to airway narrowing during late asthmatic responses and the increase in airways responsiveness (13) by release of newly formed mediators (14, IS) and a number of granule-derived toxic basic proteins (16-19). It is generally believed that eosinophils are recruited to sites of allergic inflammation as a consequence of the release of chemotactic factors after IgE-dependent mast cell activation (20, 21). However, recent studies have implicated T cells and'l-cell-derived cytokines in late responses occurring in the skin and nose (22-2S). Interleukin-S (IL-S), granulocyte/macrophage colony-stimulating factor (GM-CSF), and IL-3 promote in vitro eosino-