Blockade of avidity and focal clustering of β2-integrin by cysteinyl leukotriene antagonism attenuates eosinophil adhesion

BackgroundCysteinyl leukotriene (cysLT) antagonism attenuates migration of eosinophils into airways during immune challenge in human subjects and animal models. The intracellular signaling mechanism by which this occurs has not been elucidated.ObjectiveWe sought to determine the relative efficacy and mechanism by which 5-lipoxygenase (5-LO) inhibition and cysLT1 receptor (cysLT1R) antagonism block β2-integrin adhesion in isolated human eosinophils in vitro.MethodsHuman blood eosinophils were isolated by means of immunomagnetic separation. Upregulation of CD11b expression, active conformation of CD11b, and focal clustering of β2-integrin caused by IL-5, eotaxin-1 or leukotriene (LT) B4 was assessed by means of flow cytometry and confocal microscopy. The effect and mechanism of cysLT1R or 5-LO blockade on these components of β2-integrin adhesion were determined.ResultsMontelukast, a cysLT1R antagonist, and AA861, a 5-LO enzyme inhibitor, blocked (1) avidity of β2-integrin, (2) β2-integrin–mediated adhesion to intercellular adhesion molecule 1, and (3) focal clustering of CD11b elicited by LTB4. However, adhesion caused by either IL-5 or eotaxin-1 was not attenuated for eosinophils pretreated with either montelukast or AA861.ConclusionOur data demonstrate that (1) LTB4 causes autocrine upregulation of adhesion through secretion of cysLTs, and (2) blockade of cysLT1R blocks the avidity and focal clustering of CD11b/CD18 for eosinophils activated by LTB4 but not by IL-5 or eotaxin-1.Clinical implicationsUnlike cysLT-induced adhesion, adhesion caused by IL-5 or eotaxin-1 is not regulated through the cysLT1R, suggesting that cysLTs have specific but limited potential to upregulate eosinophil adhesion.