The effect of transendothelial migration on eosinophil function

In bronchial asthma, eosinophils found in the airways have an enhanced infl ammatory capacity. We hypothesized that, at least in part, changes in funct ional phenotype are due to the effect of transendothelial migration. To mod el in vivo eosinophil trafficking to the lung, we cultured human pulmonary microvascular endothelial cell (HPMEC) monolayers on Transwell filters. The HPMECs were activated with interleukin (IL)-1 beta to increase cell expres sion of intercellular adhesion molecule (ICAM)-1 and, hence, eosinophil tra nsmigration. Peripheral blood eosinophils from allergic patients were added to HPMEC-covered Transwell filters and incubated for 3 h at 37 degrees C. The eosinophils were collected from below (migrated cells) and above (nonmi grated cells) the HPMEC monolayer to determine surface receptor expression, in vitro survival, and oxidative burst. Eosinophils never exposed to HPMEC s were used as controls. Eosinophil cell surface expression of CD69, human leukocyte-associated antigen-DR (HLA-DR), and CD54 (ICAM-1) was significant ly increased after transendothelial migration through IL-1 beta-treated HPM ECs compared with control cells (CD69: P < 0.0005; HLA-DR and CD54: P < 0.0 5) and nonmigrated eosinophils (CD69 and HLA-DR: P < 0.05). Moreover, the p ercent in vitro survival (48 h) of migrated eosinophils was also significan tly greater (P < 0.0001 by trypan blue exclusion, P < 0.05 by flow cytometr y) than that of control or nonmigrated eosinophils. Prolonged survival of m igrated eosinophils was inhibited by addition of anti-granulocyte macrophag e colony-stimulating factor (GM-CSF) antibodies (P < 0.05) to the 48-h surv ival culture, suggesting that autocrine production of GM-CSF was, at least partially, responsible for increased eosinophil survival. Although GM-CSF p rotein was not measurable in survival culture supernates, CM-CSF messenger RNA (mRNA) was expressed in both nonmigrated and migrated eosinophils but n ot in control cells. Similarly, the eosinophils' oxidative burst induced by platelet-activating factor, formylmethionyl leucylphenylalanine, or phorbo l myristate acetate was equally, and significantly, increased in both nonmi grated and migrated eosinophils (P < 0.05 versus control). Therefore, where as exposure of eosinophils to cytokine-activated HPMECs can increase surfac e receptor expression, in vitro survival, GM-CSF mRNA, and the respiratory burst, transendothelial migration can further potentiate receptor expressio n and survival in migrated cells. These results suggest that the process of transendothelial migration selectively participates in determining the eve ntual phenotype of airway eosinophils.