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 methy l ester (L-NAME), inhibits both rat and human eosinophil chemotaxis in vitr o. Here, the role of nitric oxide (NO) in human eosinophil cell surface int egrin expression and function was investigated. 2 Human peripheral blood eosinophils were treated With L-NAME (0.01 - 1.0 m M) 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%, r espectively, when eosinophils were treated with 1.0 mM L-NAME. Increased ad hesion 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 eosi nophil adhesion to fibronectin and serum by 34.3 +/-4.5 and 45.2 +/-5.6%, r espectively. This inhibition was accompanied by a 4 fold increase in the le vels 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 quino xatin-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 cou ld also be inhibited by co-incubation with the Mac-1 and VLA-4-specific mAb s. 6 In conclusion, results indicate that NO, via a cyclic GMP-dependent mecha nism, inhibits the adhesion of human eosinophils to the extracellular matri x (ECM). This inhibition is accompanied by a decrease in the expression and function of the eosinophil's adhesion molecules, in particular, the expres sion of the Mac-1 integrin and the function of the VLA-4 integrin.