Divalent cation regulation of the function of the leukocyte integrin LFA-1.

Abstract

Abstract. The integrin lymphocyte function-associated antigen-1 (LFA-1) expressed on T cells serves as a useful model for analysis of leukocyte integrin functional activity. We have assessed the role of divalent cations Mg", Call, and Mn2+ in LFA-1 binding to ligand intercellular adhesion molecule-1 (ICAM-1) and induction of the divalent cation-dependent epitope recognized by mAb 24 . Manganese strongly promoted both expression of the 24 epitope and T cell binding to ICAM-1 via LFA1, suggesting that Mn2+ is able to directly alter the conformation of LFA1 in a manner that favors ligand binding. Since Mn2+ also promotes functional activity of other integrins, parallels in mechanism of ligand binding may span the integrin family. In contrast, induction of 24 epitope expression by Mg 21 required removal of Ca 2+ from T cell LFA1 with

Identification and characterization of a human monoclonal antagonistic antibody AL-57 that preferentially binds the high-affinity form of lymphocyte function-associated antigen-1

“…Like AL-57, ICAM-1 binds the IA I domain with IA (K d of 3-9 M), lower than that of the HA I domain (K d of 150 -360 nM) [22]. [29,43,44]. Our data with PMA were consistent with the detection of increased affinity for ligand after PMA stimulation, as measured by a sensitive ligand displacement assay using radiolabeled Fab fragments against the ␣ L subunit [18].…”

“…To minimize background caused by FcR binding, AL-57 IgG4 was used in the binding assay. Before staining with the antibody, PBMCs were incubated with inactivating buffer containing 2 mM CaCl 2 and 2 mM MgCl 2 [29,31,32]. Consistent with its specificity for the HA I domain, AL-57 IgG4 showed no binding to PBMCs in inactivating buffer but showed some binding in activating buffer (Fig.…”

Distinct Roles for the α and β Subunits in the Functions of Integrin αMβ2

“…A second manifestation of the MIDAS contribution is that different divalent cations exert differential effects on ligand binding. Mn 2ϩ enhances ligand binding function, Mg 2ϩ supports it, and Ca 2ϩ can be suppressive (35)(36)(37). The crystal structures of the ␣ M I domain or other I domains show that different cations differentially influence structure (29).…”

Immune Complex-induced Integrin Activation and L-plastin Phosphorylation Require Protein Kinase A

“…IC-induced activation of the leukocyte-specific integrin ␣ M ␤ 2 (Mac-1, CD11b/CD18) is required both for sustained adhesion to IC in vitro (12,16) and for a normal IC-induced inflammatory response in vivo (17). Thus, IC-induced ␣ M ␤ 2 activation is probably a critical event in an- 1 The abbreviations used are: PI 3-kinase, phosphatidylinositol 3-kinase; Fc␥R, receptor for the Fc piece of IgG; fMLP, formylmethionylleucylphenylalanine; IC, immune complex(es); LPL, L-plastin; PKA, cAMP-dependent protein kinase A; PKG, cGMP-dependent protein kinase G; PMA, phorbol 12-myristate 13-acetate; PMN, polymorphonuclear neutrophil(s); mPMN, murine PMN; S5A, synthetic peptide based on amino acids 2-19 of LPL in which Ser 5 has been changed to Ala; S7A, synthetic peptide based on amino acids 2-19 of LPL in which Ser 7 has been changed to Ala; SCR, synthetic peptide in which amino acids 2-19 of LPL have been scrambled; PKC, protein kinase C; 8-Br-cAMP and -cGMP, 8-bromo-cyclic AMP and GMP, respectively; HBSS, Hanks' balanced salt solution; BSA, bovine serum albumin.…”