Induction of LFA-1-dependent neutrophil rolling on ICAM-1 by engagement of E-selectin

Objective: To study rolling of mouse neutrophils on E-selectin and ICAM-1 in an ex vivo flow chamber system. Methods: The authors developed a small autoperfused flow chamber (20 × 200-μm cross section) that allows direct visualization of cells with and without fluorescent labeling and does not require recirculation of blood. Results: Neutrophils rolled on E-selectin alone, but were unable to interact with immobilized ICAM-1. When ICAM-1 was co-immobilized with E-selectin, the number of cells that rolled was doubled, but no significant firm adhesion was observed. This phenomenon was specific for E-selectin, and no enhancement of rolling was observed when P-selectin was immobilized with ICAM-1. The increased neutrophil rolling seen on E-selectin and ICAM-1 substrates required β₂ integrins. Treating mice with antibodies to the β₂ integrins LFA-1 and Mac-1 showed that LFA-1 was primarily responsible for mediating rolling on ICAM-1 in this model. Increased rolling on E-selectin and ICAM-1 was significantly reduced following administration of a specific p38 mitogen-activated protein kinase (MAPK) inhibitor. Conclusion: The data show that neutrophil rolling on E-selectin leads to partial activation of LFA-1, enabling LFA-1-dependent rolling on ICAM-1. This mechanism is likely to amplify and accelerate neutrophil recruitment in inflammation.