BACKGROUND: Allergic and nonallergic rhinitis with eosinophilia syndrome are characterized by tissue eosinophilia and nasal mucosal injury. Recently, it has been shown that the adherence of eosinophils and other leukocytes to epithelial cells is mediated by intercellular adhesion molecule-1 (ICAM-1) and related adherence-promoting glycoproteins. METHODS: In this study we examined the constitutive expression of ICAM-1 on human nasal epithelial cells (HNECs), and the effects of interferon-gamma, tumor necrosis factor-gamma eosinophil major basic protein, and eosinophil cationic protein on the regulation of ICAM-1 expression on these cells. Similar studies were performed with A549 pneumocytes as comparative epithelial cells. RESULTS: Constitutive expression of ICAM-1 was significantly higher on cultured HNECs than on A549 cells, although nasal epithelial cells in tissue specimens did not demonstrate detectable levels of ICAM-1. This spontaneous expression of ICAM-1 on cultured HNECs may explain the unique susceptibility of the nasal mucosa to rhinovirus infection, because ICAM-1 is the epithelial cell receptor for most rhinoviruses. Physiologic concentrations of major basic protein and eosinophil cationic protein stimulated significant upregulation of ICAM-1 on HNECs, which was comparable to that produced by interferon-gamma and tumor necrosis factor-alpha. In contrast, these eosinophil constituents did not stimulate ICAM-1 upregulation on A549 alveolar epithelial cells, although A549 cells did respond to interferon-gamma and tumor necrosis factor-alpha. CONCLUSION: The observation that eosinophil products upregulate ICAM-1 on HNECs suggests a positive feedback mechanism, in which the products released from migrating eosinophils might promote additional HNEC-leukocyte adherence by enhancing interactions between leukocyte beta 2 integrins (CD11/18) and nasal epithelial ICAM-1.