Dynamic Regulation of LFA-1 Activation and Neutrophil Arrest on Intercellular Adhesion Molecule 1 (ICAM-1) in Shear Flow

Abstract

Neutrophil recruitment during acute inflammation is triggered by G-protein-linked chemotactic receptors that in turn activate ␤ 2 integrin (CD18), deemed a critical step in facilitating cell capture and arrest under the shear force of blood flow. A conformational switch in the I domain allosteric site (IDAS) and in CD18 regulates LFA-1 affinity for endothelial ligands including intercellular adhesion molecule 1 (ICAM-1). We examined the dynamics of CD18 activation in terms of the efficiency of neutrophil capture of ICAM-1, and we correlated this with the membrane topography of 327C, an antibody that recognizes the active conformation of CD18 I-like domain. Adhesion increased in direct proportion to chemotactic stimulus rising 7-fold over a log range of interleukin-8 (IL-8). A threshold dose of ϳ75 pM IL-8, corresponding to ligation of only ϳ10 -100 receptors, was sufficient to activate ϳ20,000 CD18 and a rapid boost in the capture efficiency on ICAM-1. This was accompanied by a rapid redistribution of active LFA-1, but not Mac-1, into membrane patches, a necessary component for optimum adhesion efficiency. Shear-resistant arrest on a monolayer of ICAM-1 was reversed within minutes of chemotactic stimulation correlating with a shift from high to low affinity CD18 and dispersal of patches of active CD18. Mobility of active CD18 into high avidity patches was dependent on phosphatidylinositol 3-kinase activity and not F-actin polymerization. The data reveal that the number of chemotactic receptors bound and the topography and lifetime of high affinity LFA-1 tightly regulate the efficiency of neutrophil capture on ICAM-1.Neutrophils are among the first cells to respond to acute inflammation through a multistep process of specific bond formation with adhesion molecules up-regulated on the surface of activated endothelium (1, 2). Endothelial and leukocyte selectins function to capture leukocytes from the circulation by rapid bond formation. However, selectins form transient bonds that last a second or less in shear flow and only mediate cell capture and rolling on endothelium (3, 4). Unlike selectins, ␤ 2 integrins (CD18) do not constitutively recognize ligand but require cellular activation to form stable shear-resistant bonds with endothelial ligands including ICAM-1.

Inflammatory potential of neutrophils detected in sickle cell disease

“…Recently, we reported that neutrophil arrest on the endothelial ligand ICAM-1 is tightly controlled by IL-8 receptor occupancy and CD18 activation [18]. Adhesion was triggered by stimulating neutrophils with a threshold concentration of IL-8 ($0.1 nM) and increased 4-fold up to maximal adhesion at 1 nM of stimulation [18].…”

The CD11a and Endothelial Protein C Receptor Marker Combination Simplifies and Improves the Purification of Mouse Hematopoietic Stem Cells

“…CD11a (integrin alpha L, or Itgal ) heterodimerizes with the β2‐integrin CD18 to form LFA1. LFA1 interacts with ICAM‐1 and has roles in transendothelial migration, activation, and differentiation of lymphocytes 15, 16, 17, 18. We found that while CD11a is expressed on nearly all hematopoietic lineages, it is downregulated on HSCs 19.…”

Vascular mimetics based on microfluidics for imaging the leukocyte–endothelial inflammatory response

“…This weakening of adhesion strength correlates with a reversibility in high affinity b2 integrin as reported for neutrophils exposed to soluble IL-8 over the same timecourse. 29 In contrast, exposure to a concentration of 0.01 nM or lower IL-8 had no detectable impact on neutrophil arrest efficiency over the course of 3 min. Neutrophil arrest to an L-E monolayer is dependent on the activation of the b2-integrin Mac-1, which is rapidly upregulated on the plasma membrane upon neutrophil activation.…”

“…Based on our previously reported relation between chemokine concentration and integrin activation, we estimate that as few as 15 000 active b2 integrins on the surface of a neutrophil are capable of effecting arrest. 29 The reversibility of adhesion strength following chemokine exposure reveals that neutrophil recruitment from the circulation requires precise cooperation between chemotactic signal and the ligation and activation of integrins.…”