A new antihistamine levocetirizine inhibits eosinophil adhesion to vascular cell adhesion molecule-1 under flow conditions

Summary Background We previously demonstrated that low concentrations of a new antihistamine levocetirizine inhibited eosinophil transmigration through human microvascular endothelial cells. Objective Here, the inhibitory effect of levocetirizine on eosinophil adhesion to recombinant human vascular cell adhesion molecule‐1 (rhVCAM)‐1 was examined under conditions of shear stress using an in vitro model of the post‐capillary venules. Methods Eosinophils isolated from normal subjects were pre‐incubated with a concentration range of levocetirizine (10−6–10−10 m) or negative dilution control. Resting or granulocyte macrophage‐colony stimulating factor (GM‐CSF)‐stimulated cells were pumped through rhVCAM‐1 (10 μg/mL) coated capillary tubes using a microfluidic syringe pump at a precise and constant flow rate (1 dyn/cm2). Images of rolling and firmly adherent eosinophils were captured using real‐time video microscopy. Results Levocetirizine significantly inhibited resting eosinophil adhesion to rhVCAM‐1 with maximal effect at 10−8 M with an EC50 of 10−9 m. Levocetirizine almost abolished resting eosinophil adhesion by the 15 min time‐point. GM‐CSF significantly enhanced eosinophil adhesion and their ability to flatten on rhVCAM‐1. Both phenomena were inhibited by levocetirizine in a dose‐dependent manner, at both 5 and 15 min (optimal concentration of 10−8 m with an EC50 of 10−9 m). Real‐time imaging revealed that the effect of levocetirizine on post‐adhesion behaviour (detachment, flatness) contributed to its inhibitory action on eosinophil adhesion to rhVCAM‐1. In contrast, very late antigen (VLA)‐4 mAb inhibited eosinophil adhesion to rhVCAM‐1 from the earliest time‐points. Conclusion Physiologically relevant concentrations of levocetirizine inhibit resting and GM‐CSF‐stimulated firm eosinophil adhesion to rhVCAM‐1 under flow conditions.