title: 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 beta(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 approximately 75 pm IL-8, corresponding to ligation of only approximately 10-100 receptors, was sufficient to activate approximately 20,000 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.
authors.affiliation: Department of Biomedical Engineering, University of California, Davis, California 95616, USA.
authors.forename: Aaron F H
authors.initials: AF
authors.lastname: Lum
authors.forename: Chad E
authors.initials: CE
authors.lastname: Green
authors.forename: Garrett R
authors.initials: GR
authors.lastname: Lee
authors.forename: Donald E
authors.initials: DE
authors.lastname: Staunton
authors.forename: Scott I
authors.initials: SI
authors.lastname: Simon
mesh_terms: D000328:Adult; D000494:Allosteric Regulation; D000911:Antibodies, Monoclonal / Q000276:immunology; D018821:CD18 Antigens / Q000276:immunology; D002118:Calcium / Q000378:metabolism; D002634:Chemotaxis, Leukocyte; D005455:Fluorescent Antibody Technique; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D016209:Interleukin-8 / Q000494:pharmacology; D017136:Ion Transport; D007700:Kinetics; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D018375:Neutrophil Activation / Q000187:drug effects; D009504:Neutrophils / Q000166:cytology* / Q000187:drug effects
chemical_list: D000911:Antibodies, Monoclonal; D018821:CD18 Antigens; D016209:Interleukin-8; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1; D002118:Calcium