Kinetics of LFA-1 mediated adhesion of human neutrophils to ICAM-1--role of E-selectin signaling post-activation.

LFA-1 and Mac-1 are the two integrins involved in the arrest and firm adhesion of neutrophils. LFA-1 plays a role in the early stage of cell arrest while Mac-1 stabilizes firm adhesion. Here, we further elucidated the kinetics of LFA-1 activation and its role in mediating neutrophil adhesion to ICAM-1 in the presence of E-selectin interaction. We confirm that LFA-1 activation to high affinity is transient in nature, decaying back to low affinity within 1 min after chemotactic stimulation. However, we show for the first time that this downshift in LFA-1 affinity does not return back to the low affinity state when E-selectin interaction is present and active, but rather E-selectin signals an intermediate LFA-1 conformation through PI3-Kinase that maintains an intermediate level of neutrophil firm adhesion. We further show that this E-selectin signaling is capable of returning LFA-1 to the intermediate affinity conformation outside the 1-min window previously reported for LFA-1 functionality. While our work confirms a role for PI3-Kinase in neutrophil firm adhesion, we show that PI3-Kinase may not be important in the initial transition from rolling to firm arrest (i.e. LFA-1 shift from low to high affinity conformation occurring within seconds of chemotactic stimulation).