title: Direct evidence for two affinity states for lymphocyte function-associated antigen 1 on activated T cells.
abstract: Lymphocytes activated by antigen receptor cross-linking or phorbol esters adhere avidly to surfaces bearing intercellular adhesion molecule 1 (ICAM-1) through the adhesion receptor lymphocyte function-associated antigen 1 (LFA-1). It is not known whether avid adhesion by stimulated lymphocytes is due to higher affinity binding of ICAM-1 or due solely to post-receptor mechanisms. We have used a recombinant, soluble form of the ICAM-1 molecule to measure the affinity of binding to LFA-1 on unstimulated T cells and T cells stimulated with phorbol esters. The affinity was found to be too low for direct measurements, requiring instead the use of competition protocols in which ICAM-1 competes for binding with radiolabeled Fab from a monoclonal antibody specific for LFA-1. By analysis of the equilibrium and kinetics of competitive binding, we found that the affinity on unstimulated T cells is very low, about 100 microM. Activation of the T cells by phorbol esters caused a small increase in average binding affinity. Further analysis suggested that the change in average affinity reflected the conversion of a fraction of LFA-1 molecules to a state with a 200-fold higher affinity.
authors.affiliation: Department of Chemistry, University of California at San Diego, La Jolla 92093-0063.
authors.forename: B A
authors.initials: BA
authors.lastname: Lollo
authors.forename: K W
authors.initials: KW
authors.lastname: Chan
authors.forename: E M
authors.initials: EM
authors.lastname: Hanson
authors.forename: V T
authors.initials: VT
authors.lastname: Moy
authors.forename: A A
authors.initials: AA
authors.lastname: Brian
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002460:Cell Line; D006825:Hybridomas; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D018799:Intercellular Adhesion Molecule-1; D007700:Kinetics; D008213:Lymphocyte Activation; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D051379:Mice; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D015815:Cell Adhesion Molecules; D007140:Immunoglobulin Fab Fragments; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1; D013755:Tetradecanoylphorbol Acetate