The LFA-1 Integrin Supports Rolling Adhesions on ICAM-1 Under Physiological Shear Flow in a Permissive Cellular Environment

Abstract

The LFA-1 integrin is crucial for the firm adhesion of circulating leukocytes to ICAM-1-expressing endothelial cells. In the present study, we demonstrate that LFA-1 can arrest unstimulated PBL subsets and lymphoblastoid Jurkat cells on immobilized ICAM-1 under subphysiological shear flow and mediate firm adhesion to ICAM-1 after short static contact. However, LFA-1 expressed in K562 cells failed to support firm adhesion to ICAM-1 but instead mediated K562 cell rolling on the endothelial ligand under physiological shear stress. LFA-1-mediated rolling required an intact LFA-1 I-domain, was enhanced by Mg2+, and was sharply dependent on ICAM-1 density. This is the first indication that LFA-1 can engage in rolling adhesions with ICAM-1 under physiological shear flow. The ability of LFA-1 to support rolling correlates with decreased avidity and impaired time-dependent adhesion strengthening. A β2 cytoplasmic domain-deletion mutant of LFA-1, with high avidity to immobilized ICAM-1, mediated firm arrests of K562 cells interacting with ICAM-1 under shear flow. Our results suggest that restrictions in LFA-1 clustering mediated by cytoskeletal attachments may lock the integrin into low-avidity states in particular cellular environments. Although low-avidity LFA-1 states fail to undergo adhesion strengthening upon contact with ICAM-1 at stasis, these states are permissive for leukocyte rolling on ICAM-1 under physiological shear flow. Rolling mediated by low-avidity LFA-1 interactions with ICAM-1 may stabilize rolling initiated by specialized vascular rolling receptors and allow the leukocyte to arrest on vascular endothelium upon exposure to stimulatory endothelial signals.

RhoA Is Involved in LFA-1 Extension Triggered by CXCL12 but Not in a Novel Outside-In LFA-1 Activation Facilitated by CXCL9

“…Substrates were subsequently overlaid with various concentrations of ICAM-1-Fc. Ligand densities were assessed as previously described (25). Isolated T cells were washed in 5 mM EDTA containing medium and were suspended in H/H medium (HBSS containing 2 mg/ml BSA and 10 mM HEPES, pH 7.4) in the presence of the indicated peptides or reagents.…”

Talin 1 and Paxillin Facilitate Distinct Steps in Rapid VLA-4-mediated Adhesion Strengthening to Vascular Cell Adhesion Molecule 1

“…Site densities of coated sVCAM-1 were determined as described (25,27). The polystyrene plates were each assembled on the lower wall of the flow chamber (260-m gap) (28).…”

The CD81 Tetraspanin Facilitates Instantaneous Leukocyte VLA-4 Adhesion Strengthening to Vascular Cell Adhesion Molecule 1 (VCAM-1) under Shear Flow

“…However, the ability of VLA-4 to tether cells and support their rolling on the endothelial ligand, VCAM-1, 1 under shear flow does not require high affinity to soluble ligands (9). In addition, previous studies suggested that VLA-4 and LFA-1 associations with the intracellular actincytoskeleton control integrin adhesiveness to ligand under shear flow and are independent of the intrinsic affinity of these integrins to their respective ligands (5,6). Accordingly, the ability of leukocyte integrins to self-cluster upon ligand binding has been predicted to facilitate the generation of high avidity tethers under disruptive shear forces even without acquisition of conformations with high affinity to monovalent ligands (10).…”

“…The firm adhesions are mediated exclusively by subsets of leukocyte integrins, which include ␣ 4 ␤ 7 , VLA-4 (␣ 4 ␤ 1 ), and LFA-1 (3,4). These integrins exhibit basal recognition of ligand under shear flow and enable leukocyte capture, rolling, and arrest on their respective endothelial ligands when present at sufficiently high densities (5,6). This basal integrin adhesiveness can be dramatically augmented by leukocyte exposure to appropriate endothelial chemokines in situ, which enhance integrin avidity through their respective G-protein-coupled receptors on tethered leukocytes (7,8).…”