Eosinophil adhesion to airway epithelium is believed to facilitate eosinophil accumulation and retention in asthmatic airways. Monoclonal antibodies (mAb) against intercellular adhesion molecule-1 (ICAM-1) and its CD18 leukocyte integrin ligands have been shown to inhibit airway eosinophilia in animal models of asthma, although the role of this pathway in eosinophil-epithelial adhesion is not fully understood. To investigate the role in vitro of CD18 and ICAM-1, we measured adhesion of fluorescently labeled human eosinophils to normal human bronchial epithelial cell (NHBEC) monolayers pretreated for 24 h with culture medium (low constitutive ICAM-1) or tumor necrosis factor-alpha (TNF-alpha; 1 ng/ml) and interferon-gamma (IFN-gamma) (10 ng/ml; increased ICAM-1). Stimulation of eosinophils with C5a (10(-7) M) increased adhesion measured at 30 min to unactivated NHBEC from 11.4 +/- 0.7 to 15.5 +/- 0.4% (n = 4), and this increase was CD18/ICAM-1-independent, whereas phorbolmyristate acetate (PMA) (10(-8) M)-induced adhesion (20.7 +/- 1.7%) was abolished by anti-CD18 and reduced by anti-ICAM-1. In contrast, C5a- and PMA-induced adhesion to TNF-alpha/IFN-gamma-activated NHBEC (increased from 11.1 +/- 1.3% to 21.9 +/- 1.0% and 27.6 +/- 1.9%, respectively) was CD18- and ICAM-1-dependent. Eotaxin, but not regulated on activation normal T cells expressed and secreted, macrophage inflammatory protein-1, formyl methionyl leucyl phenylalanine, leukotriene B4 or platelet-activating factor, also induced CD18/ICAM-1-dependent adhesion to activated NHBEC. In the absence of added chemoattractants, eosinophil adhesion to NHBEC increased with time and, at 120 min, was significantly greater (P < 0.01) to activated NHBEC (37.3 +/- 2.4%, n = 5) than to unactivated monolayers (24.3 +/- 1.9%); mAb against CD18 or ICAM-1 abolished increased, but not basal, adhesion. These results suggest that CD18/ICAM-1 mediated eosinophil adhesion to activated NHBEC but that adhesion to resting NHBEC was largely independent of this pathway.