Signaling functions of L-selectin in neutrophils: Alterations in the cytoskeleton and colocalization with CD18

Ligation and clustering of L-selectin by Ab ("cross-linking") or physiologi c ligands results in activation of diverse responses that favor enhanced mi crovascular sequestration and emigration of neutrophils, The earliest respo nses include a rise in intracellular calcium, enhanced tyrosine phosphoryla tion, and activation of extracellular signal-regulated kinases. Additionall y, cross-linking of L-selectin induces sustained shape change and activatio n of beta(2) integrins, leading to neutrophil arrest under conditions of sh ear flow. In this report, we examined several possible mechanisms whereby t ransmembrane signals from L-selectin might contribute to an increase in the microvascular retention of neutrophils and enhanced efficiency of emigrati on. In human peripheral blood neutrophils, cross-linking of L-selectin indu ced alterations in cellular biophysical properties, including a decrease in cell deformability associated with F-actin assembly and redistribution, as well as enhanced adhesion of microspheres bound to beta(2) integrins, L-se lectin and the beta(2) integrin became spatially colocalized as determined by confocal immunofluorescence microscopy and fluorescence resonance energy transfer. We conclude that intracellular signals from L-selectin may enhan ce the microvascular sequestration of neutrophils at sites of inflammation through a combination of cytoskeletal alterations leading to cell stiffenin g and an increase in adhesiveness mediated through alterations in beta(2) i ntegrins.