Dynamic shifts in LFA-1 affinity regulate neutrophil rolling, arrest, and transmigration on inflamed endothelium

Abstract

Polymorphonuclear leukocyte (PMN) recruitment to vascular endothelium during acute inflammation involves cooperation between selectins, G-proteins, and ␤ 2 -integrins. LFA-1 (CD11a/CD18) affinity correlates with specific adhesion functions because a shift from low to intermediate affinity supports rolling on ICAM-1, whereas high affinity is associated with shear-resistant leukocyte arrest. We imaged PMN adhesion on cytokine-inflamed endothelium in a parallel-plate flow chamber to define the dynamics of ␤ 2 -integrin function during recruitment and transmigration. After arrest on inflamed endothelium, high-affinity LFA-1 aligned along the uropod-pseudopod major axis, which was essential for efficient neutrophil polarization and subsequent transmigration. IntroductionNeutrophils are recruited at vascular sites of acute inflammation by the sequential binding of selectins, CXC chemokines, and ␤ 2 -integrins that function cooperatively to elicit rolling, arrest, and transmigration. From observations of neutrophil recruitment in the murine microcirculation and on endothelial monolayers grown in tissue culture, a number of rules of engagement have emerged. First, Mac-1 (␣ M ␤ 2 ) and LFA-1 (␣ L ␤ 2 ) are necessary and sufficient for neutrophil arrest and transmigration, with each subunit providing distinct adhesive contributions throughout the process from rolling to transmigration. 1-3 Second, polymorphonuclear leukocyte (PMN) rolling on a monolayer of cells coexpressing E-selectin and intercellular adhesion molecule-1 (ICAM-1) is sufficient to induce selectin ligand clustering (PSGL-1 and L-selectin) and to signal a shift in LFA-1 and Mac-1 from low to high affinity to bind ICAM-1. This process is synergistic with chemokine signaling on rolling PMN to amplify the efficiency of arrest. 4,5 LFA-1 appears to function early in this process in that it participates in tethering to ICAM-1 as it shifts from low to intermediate and high affinity. 6,7 How changes in conformation of the heterodimer result in changes in affinity to interact with ICAM-1 and mediate rolling, arrest, and outside-in signaling is only partially defined. 8 Structural studies of LFA-1 reveal that extension and activation of ICAM-1 binding involves an inserted or I-domain on the ␣-subunit and an I-like domain on the ␤-subunit that exerts a pull on the C-terminal ␣ 7 -helix of the ␣-subunit, leading to the open shape of the heterodimer and high-affinity ligand binding. 9,[10][11][12] This conformational shift to high affinity can be stabilized by binding of Mg 2ϩ or Mn 2ϩ or by inside-out signaling by chemokine receptors. 9,13,14 Once activated by a chemokine such as IL-8 or SDF-1, extension and opening of the LFA-1 heterodimer initiate rapid arrest on ICAM-1, as do activated I-domain mutants. 6,[15][16][17][18] Counteracting a shift to high affinity, small molecule allosteric anti-inflammatory inhibitors of LFA-1 function by effectively stabilizing the low-affinity state and antagonize binding to ICAM-1 and leukocyte adhesion. 19,20 XVA143 is one such ...

β2 Integrin–Mediated Crawling on Endothelial ICAM-1 and ICAM-2 Is a Prerequisite for Transcellular Neutrophil Diapedesis across the Inflamed Blood–Brain Barrier

“…In our study, LFA-1 was found to be the prevailing integrin mediating shear-resistant arrest of neutrophils on the LPS-stimulated BBB. Our results are in accordance with previous observations in which LFA-1 was shown to mediate arrest of human neutrophils on inflamed HUVECs under flow in vitro (50) and of neutrophils in inflamed cremaster muscle venules in vivo (20). Thus, LFA-1 mediates shear-resistant arrest of neutrophils on inflamed endothelial cells in different vascular beds.…”

Sickle red cells induce adhesion of lymphocytes and monocytes to endothelium

“…36,37 We therefore evaluated whether SS RBCs induced leukocyte ␤2 integrins and CD44 to mediate PBMC adhesion to ECs. Incubation of PBMCs with antibodies against ␤2 integrins and CD44 significantly inhibited (80% Ϯ 2.3% and 83% Ϯ 4.5% inhibition, respectively; P Ͻ .001) subsequent adhesion to ECs of activated PBMCs washed free of lysed epinephrine-treated SS RBCs ( Figure 4A,B).…”

Rolling on E- or P-selectin induces the extended but not high-affinity conformation of LFA-1 in neutrophils

“…[1][2][3] In Ficoll-isolated human neutrophils, this process leads to arrest from rolling, polarization, and firm adhesion to endothelial monolayers under flow. [4][5][6][7] The proximal signal transduction pathway leading from E-selectin binding to integrin-dependent adhesion is unknown. Whether neutrophil integrins assume the extended or high affinity conformation is also unknown.…”