Nitric oxide regulates human eosinophil adhesion mechanisms in vitro by changing integrin expression and activity on the eosinophil cell surface

1 The nitric oxide synthase (NOS) inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME), inhibits both rat and human eosinophil chemotaxis in vitro. Here, the role of nitric oxide (NO) in human eosinophil cell surface integrin expression and function was investigated. 2 Human peripheral blood eosinophils were treated With L-NAME (0.01 - 1.0 mM) and their adhesion to human fibronectin and serum observed. Adhesion of cells to fibronectin and serum increased by 24.0 +/-4.6 and 43.8 +/-4.7%, respectively, when eosinophils were treated with 1.0 mM L-NAME. Increased adhesion by L-NAME could be abolished when cells were co-incubated with VLA-4- and Mac-1-specific monoclonal antibodies (mAbs). 3 The NO donor, sodium nitroprusside (2.5 mM), significantly inhibited eosinophil adhesion to fibronectin and serum by 34.3 +/-4.5 and 45.2 +/-5.6%, respectively. This inhibition was accompanied by a 4 fold increase in the levels of intracellular cyclic GMP. 4 Flow cytometrical analysis demonstrated that L-NAME induced an increased expression of CD11b (Mac-1) on the eosinophil cell surface of 36.3 +/-7.4%, L-NAME had no effect upon CD49d (VLA-4) expression. 5 Treatment of human eosinophils, in vitro, with H-[1,2,4] oxadiazolo quinoxatin-1-one (ODQ) (0.1 mM), an inhibitor of soluble guanylate cyclase, also significantly increased eosinophil adhesion to fibronectin and serum by 73.5 +/- 17.9 and 91.7 +/- 12.9%, respectively. This increase in adhesion could also be inhibited by co-incubation with the Mac-1 and VLA-4-specific mAbs. 6 In conclusion, results indicate that NO, via a cyclic GMP-dependent mechanism, inhibits the adhesion of human eosinophils to the extracellular matrix (ECM). This inhibition is accompanied by a decrease in the expression and function of the eosinophil's adhesion molecules, in particular, the expression of the Mac-1 integrin and the function of the VLA-4 integrin.