Direct evidence for two affinity states for lymphocyte function-associated antigen 1 on activated T cells

• Published in: The Journal of biological chemistry 1993-10, Vol.268 (29), p.21693-21700
• Main Authors: LOLLO, B. A, CHAN, K. W. H, HANSON, E. M, MOY, V. T, BRIAN, A. A
• Format: Article
• Language: English
• Subjects: Animals; Binding, Competitive; Biological and medical sciences; Cell Adhesion Molecules - metabolism; Cell Line; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Hybridomas; Immunobiology; Immunoglobulin Fab Fragments - metabolism; Intercellular Adhesion Molecule-1; Kinetics; Lymphocyte Activation; Lymphocyte Function-Associated Antigen-1 - metabolism; Lymphoid cells: ontogeny, maturation, markers, receptors, circulation and recirculation; Mice; T-Lymphocytes - drug effects; T-Lymphocytes - immunology; T-Lymphocytes - metabolism; Tetradecanoylphorbol Acetate - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(20)80597-3

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.