Regulation of human eosinophil transmigration across lung epithelium

Sammanfattning: Eosinophil infiltration into the lung tissues and airways is a hallmark of allergic asthma. To reach the lung lumen, eosinophils migrate across the vascular endothelium, through the interstitial matrix and across lung epithelium. The present investigation deals with the regulatory mechanisms of human eosinophil transmigration across lung epithelium. The model used consisted of human lung epithelial cell monolayers grown to confluence on a permeable membrane support, through which purified eosinophils were made to migrate toward chemoattractants placed on the opposite side of the membrane. Pronounced eosinophil transepithelial migration was induced when platelet-activating factor (PAF) was combined with another eosinophil chemoattractant such as complement fragment C5a. In this transmigration process, PAF acts as both a chemoattractant and a priming agent for eosinophils. PAF also activates lung epithelial cells to regulate eosinophil transmigration. Because neutrophils are involved and infiltrate the lungs during an asthma attack, the transmigration of eosinophils in the presence of neutrophils was also investigated. Neutrophils dramatically enhanced eosinophil transepithelial migration toward the complement fragment C5a, but not toward other chemoattractants. The results suggest that human neutrophils are able to maintain the steepness of the C5a chemotactic gradient across an epithielial monolayer by inactivating diffused C5a, thus facilitating eosinophil transmigration. In this study, the role of Ca2+ in eosinophil transmigration across lung epithelial monolayers was investigated. We show a distinctive regulatory role of intracellular and extracellular Ca2+ for each of the two cell types involved in this process. The transmigration of human eosinophils across a lung epithelial cell monolayer is regulated by the intracellular Ca2+ in eosinophils and also by the extracellular Ca2+ for the functional changes of lung epithelial cells to allow eosinophil passage. Using blocking antibodies, we found that the transmigration of human eosinophils across a lung epithelial monolayer is dependent on the α Mβ2 integrin. By inducing Ca2+ entry into eosinophils as a consequence of depletion of Ca2+ from intracellular stores, thapsigargin primes eosinophils for αMβ2 -dependent transepithelial migration. Thapsigargin-induced priming of eosinophil transepithelial migration relies on the extracellular Ca2+-mediated up-regulation of αMβ2 integrin, suggesting the importance of store-operated Ca2+ entry in the priming of eosinophil transmigration.