To study the mechanisms involved in the movement of neutrophils from the blood stream into the lung airways, we investigated human neutrophil transmigration across a monolayer of human airway epithelial cells, both in the apical-to-basolateral direction and in the more physiologic basolateral-to-apical direction. Migration of human neutrophils across monolayers of human airway epithelial H292 cell-line cells and primary bronchial epithelial cells occured most efficiently in the basolateral-to-apical direction, both after the addition of chemoattractants to resting epithelial cells and across interleukin-1beta (IL-1beta)-stimulated epithelial cells. Blocking studies with monoclonal antibodies revealed that the migration of neutrophils was mediated by the CR3 adhesion molecule (CD11b/CD18) on the neutrophils. IL-1beta-treated epithelial cells caused neutrophil movement via the secretion of chemoattractants. The most potent chemoattractant released by the epithelial cells was found to be IL-8, because the IL-1beta-induced migration was inhibited for 75 +/- 10% by the addition of an antibody against IL-8. After apical stimulation of the epithelial cells with an optimal concentration of IL-1beta, 27 +/- 4 ng/ml IL-8 was found in the supernatant at the apical side of epithelial cells. Platelet-activating factor (PAF) synthesis by the epithelial cells did not play a role in neutrophil transmigration, as was demonstrated by the lack of inhibition of this process after addition of the PAF-receptor antagonist WEB 2086. We conclude that the movement of neutrophils across airway epithelial cell monolayers occurs preferentially in the physiologic basolateral-to-apical direction, indicating that the polarity of epithelial cells is important for neutrophil transmigration.