α<inf>4</inf>-integrin (CD49d) expression on bovine peripheral blood neutrophils is related to inflammation of the respiratory system

Abstract

Neutrophil emigration from the pulmonary vasculature, is mediated by cellular adhesion molecules (CAM) expressed on the outer membranes of endothelial cells and neutrophils. Although β2-integrin-dependent migration is a major mechanism of neutrophil migration, which was demonstrated by extensive invasion of neutrophils in pulmonary tissue of calves suffering from a genetic deficit in expression of β2-integrins, termed bovine leukocyte adhesion deficiency (LAD), the role of alternative CAM is still unclear. We investigated whether an alternate CAM for β2-integrin function, i.e. the α4-integrin, was expressed on peripheral blood neutrophils of calves. As we detected basal but significant expression, the effect of naturally acquired pulmonary infection on the expression of either integrin was determined, as an indication for its function in the migration process. In our experiments, basal expression of α4-integrins on peripheral blood neutrophils from clinically healthy calves was detected. On neutrophils of calves, experiencing field outbreaks of enzootic bronchopneumonia, higher expression of the α4-integrin was detected, which returned to normal after successful treatment of the disease. In addition, its level of expression was linearly related to plasma acute phase protein (haptoglobin) concentrations, which is a sensitive parameter for severity of respiratory inflammation. Increased expression of the α4-integrin on peripheral blood neutrophils during pulmonary inflammation indicates a role for this CAM in neutrophil migration in the lung.