Direct observations in vivo on the role of endothelial selectins and α4 integrin in cytokine-induced leukocyte-endothelium interactions in the mouse aorta

Abstract

The molecular mechanisms underlying leukocyte recruitment in large arteries have been extensively studied using histological techniques on fixed tissues. However, there are no reports that address the dynamics of leukocyte recruitment in large arteries in vivo. We developed an intravital microscopy technique for direct observation of leukocyte-endothelium interactions in the mouse aorta. Circulating leukocytes were labeled intravasally with rhodamine 6G and microscopically visualized within the aorta, allowing direct analysis of leukocyte rolling and adhesion. In untreated vessels, leukocyte- endothelium interactions were virtually absent. However, local pretreatment with cytokines interleukin-1β and tumor necrosis factor-α induced clear-cut leukocyte rolling and adhesion, compatible with normal blood flow and wall shear rate. High shear decreased rolling leukocyte flux and increased leukocyte rolling velocity, thus decreasing the tendency for firm adhesion. Leukocyte rolling was almost abolished by an antibody blocking the function of P-selectin, whereas function-blocking antibodies against E-selectin and the α4-integrin subunit decreased rolling leukocyte flux to 51±34% (mean±SD) and 59±11% of the value before antibody treatment, respectively. In addition, inhibition of E-selectin function, but not of α4 integrin, resulted in increased leukocyte rolling velocity (from 48±32 to 71±32 μm per second). Taken together, we introduce the first model for direct studies of leukocyte-endothelium interactions in a large artery in vivo and demonstrate cytokine-induced shear-sensitive leukocyte rolling that is critically dependent on P-selectin and modulated by E-selectin and α4 integrin.