Bovine respiratory syncytial virus infection influences the impact of α<inf>4</inf>- and β<inf>2</inf>-integrin-mediated adhesion of peripheral blood neutrophils

Neutrophil migration into the airways and pulmonary tissue is a common finding in bovine respiratory syncytial virus (BRSV) infections. Although neutrophil trans-endothelial migration in general depends on β2-integrins, alternative integrins such as the α4-integrins have been implicated. In this study, rolling and firm adhesion of peripheral blood neutrophils isolated from healthy and BRSV-infected calves to tumour necrosis factor (TNF)-α activated pulmonary endothelium was investigated under flow conditions in vitro. For neutrophils obtained from healthy animals, inhibition of the β2-integrin reduced firm adhesion to 63% and inhibition of α4-integrin to 73% compared with untreated controls. Inhibition of both integrins reduced firm adhesion to 25%. Rolling velocity, which is used as a parameter for integrin involvement in neutrophil rolling, increased 1·7-fold by blocking β2-integrin and was significantly augmented to 2·5-fold by blocking both α4- and β2-integrins. For neutrophils obtained from BRSV-infected animals, however, rolling velocities at 10 days after infection (p.i.) were not influenced by blocking adhesion of α4- and β2-integrins, indicating that these integrins did not support neutrophil rolling. In addition, the inhibition of firm adhesion by blocking both α4- and β2-integrins was reduced significantly 9 days post-infection, resulting in a residual 68% neutrophil binding at 9 days p.i. Non-blocked firm adherence was not reduced, indicating that binding was achieved by other mechanisms than through α4- and β2-integrins. These results demonstrate an important function for α4- and β2-integrins in rolling and firm adherence of bovine neutrophils, to TNF-α-activated endothelium and show the dynamic use of these integrins for adhesion and migration by neutrophils in the course of BRSV infection.