A novel LFA-1 activation epitope maps to the I domain.
A panel of 21 alpha-subunit (CD11a) and 10 beta-subunit (CD18) anti-LFA-1 mAbs was screened for ability to activate LFA-1. A single anti-CD11a mAb, MEM-83, was identified which was able to directly induce the binding of T cells to purified ICAM-1 immobilized on plastic. This ICAM-1 binding could be achieved by monovalent Fab fragments of mAb MEM-83 at concentrations equivalent to whole antibody, was associated with appearance of the "activation reporter" epitope detected by mAb 24, and was completely inhibited by anti-ICAM-1 and LFA-1 blocking mAbs. The epitope recognized by mAb MEM-83 was distinct from that recognized by mAb NKI-L16, an anti-CD11a mAb previously reported to induce LFA-1 activation, in that it was constitutively present on freshly isolated peripheral blood mononuclear cells and was not divalent cation dependent for expression. The ICAM-1 binding activity induced by mAb MEM-83 was, however, dependent on the presence of Mg2+ divalent cations. Using an in vitro-translated CD11a cDNA deletion series, we have mapped the MEM-83 activation epitope to the "I" domain of the LFA-1 alpha subunit. These studies have therefore identified a novel LFA-1 activation epitope mapping to the I domain of LFA-1, thereby implicating this domain in the regulation of LFA-1 binding to ICAM-1.
Landis
R C
RC
Macrophage Laboratory, Imperial Cancer Research Fund, London, United Kingdom.
Bennett
R I
RI
Hogg
N
N
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology*; D018845:CD11 Antigens; D018821:CD18 Antigens; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002449:Cell Aggregation; D003001:Cloning, Molecular; D000939:Epitopes / Q000032:analysis*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D018799:Intercellular Adhesion Molecule-1; D008213:Lymphocyte Activation; D016169:Lymphocyte Function-Associated Antigen-1 / Q000276:immunology*; D046911:Macromolecular Substances; D016133:Polymerase Chain Reaction / Q000379:methods; D014176:Protein Biosynthesis; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013601:T-Lymphocytes / Q000276:immunology*; D014158:Transcription, Genetic
D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D015703:Antigens, CD; D018845:CD11 Antigens; D018821:CD18 Antigens; D015815:Cell Adhesion Molecules; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D016169:Lymphocyte Function-Associated Antigen-1; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D018799:Intercellular Adhesion Molecule-1