Involvement of the "I" domain of LFA-1 in selective binding to ligands ICAM-1 and ICAM-3.
To analyze the binding requirements of LFA-1 for its two most homologous ligands, ICAM-1 and ICAM-3, we compared the effects of various LFA-1 activation regimes and a panel of anti-LFA-1 mAbs in T cell binding assays to ICAM-1 or ICAM-3 coated on plastic. These studies demonstrated that T cell binding to ICAM-3 was inducible both from the exterior of the cell by Mn2+ and from the interior by an agonist of the "inside-out" signaling pathway. T cells bound both ICAM ligands with comparable avidity. A screen of 29 anti-LFA-1 mAbs led to the identification of two mAbs specific for the alpha subunit of LFA-1 which selectively blocked adhesion of T cells to ICAM-3 but not ICAM-1. These two mAbs, YTH81.5 and 122.2A5, exhibited identical blocking properties in a more defined adhesion assay using LFA-1 transfected COS cells binding to immobilized ligand. Blocking was not due to a steric interference between anti-LFA-1 mAbs and N-linked carbohydrate residues present on ICAM-3 but not ICAM-1. The epitopes of mAbs YTH81.5 and 122.2A5 were shown to map to the I domain of the LFA-1 alpha subunit. A third I domain mAb, MEM-83, has been previously reported to uniquely activate LFA-1 to bind ICAM-1 (Landis, R. C., R. I. Bennett, and N. Hogg. 1993. J. Cell Biol. 120:1519-1527). We now show that mAb MEM-83 is not able to stimulate binding of T cells to ICAM-3 over a wide concentration range. Failure to induce ICAM-3 binding by mAb MEM-83 was not due to a blockade of the ICAM-3 binding site on LFA-1. This study has demonstrated that two sets of functionally distinct mAbs recognizing epitopes in the I domain of LFA-1 are able to exert differential effects on the binding of LFA-1 to its ligands ICAM-1, and ICAM-3. These results suggest for the first time that LFA-1 is capable of binding these two highly homologous ligands in a selective manner and that the I domain plays a role in this process.
Landis
R C
RC
Leukocyte Adhesion Laboratory, Imperial Cancer Research Fund, London, United Kingdom.
McDowall
A
A
Holness
C L
CL
Littler
A J
AJ
Simmons
D L
DL
Hogg
N
N
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000378:metabolism*; D000943:Antigens, Differentiation; D002448:Cell Adhesion / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002478:Cells, Cultured; D000939:Epitopes / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D018799:Intercellular Adhesion Molecule-1; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D010703:Phorbol Esters / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013601:T-Lymphocytes / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D015815:Cell Adhesion Molecules; D000939:Epitopes; C483616:ICAM3 protein, human; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D010703:Phorbol Esters; D011993:Recombinant Fusion Proteins; D018799:Intercellular Adhesion Molecule-1; D008345:Manganese