Additive blockade of β2-integrin adhesion of eosinophils by salmeterol and fluticasone propionate

Migration of human eosinophils is regulated by integrin expression, conformational change, and activation of cytosolic phospholipase A(2) (cPLA(2)). Corticosteroids have been shown to inhibit cPLA2 hydrolysis in human eosinophils. The objective of this study was to determine the mechanisms of fluticasone propionate (FP) alone or in combination with salmeterol (SM) in blocking adhesion mediated by beta(2)-integrin in human eosinophils. Human eosinophils were isolated by negative magnetic selection. O-2-integrin-mediated eosinophil adhesion was measured by residual eosinophil peroxidase activity. Eosinophils were pretreated for 12 h to 24 with FP and with or without SM for 30 min. Both SM alone and FP alone inhibited eosinophil adhesion in concentration- and time-dependent manner. SM alone modestly (similar to30%) inhibited interleukin (IL)-5-induced eosinophil adhesion. Blockade of IL-5-induced eosinophil adhesion caused by 10(-7) M FP at 24 h was augmented by 10(-7) M SM from 41.5%, to 72.5%. Similar blockade was also observed for eotaxin-induced eosinophil adhesion. Neither SM, FP, nor FP+SM blocked either: 1) upregulation of CD11b surface expression; or 2) phosphorylation of ePLA(2). Blockade of beta(2)-integrin-mediated eosinophil adhesion by fluticasone propionate is augmented by salmeterol. Decreased adhesion results from augmented blockade of nuclear translocation of cytosolic phospholipase A(2) caused by addition of salmeterol to fluticasone.