Antibodies that selectively inhibit leukocyte function-associated antigen 1 binding to intercellular adhesion molecule-3 recognize a unique epitope within the CD11a I domain.
Several studies indicate that the I domain located in the alpha chain (CD11a) of leukocyte function-associated antigen-1 (LFA-1; CD11a/CD18) plays an essential role in ligand recognition. We recently identified three distinct epitopes (IdeA, IdeB, and IdeC) within the CD11a I domain, recognized by antibodies that block binding of LFA-1 to intercellular adhesion molecules (ICAM) 1, 2, and 3. In the present study, we used a series of human/murine CD11a I domain chimeras, to localize a fourth I domain epitope (IdeD), recognized by three independently derived anti-CD11a antibodies that selectively block the binding of LFA-1 to ICAM-3, but not to ICAM-1. The IdeD epitope depended on human CD11a residues Asp182 and Ser184 and was not present in CD11b or CD11c. Although mutation of Asp182 and Ser184 failed to abolish ICAM-3 adhesion of LFA-1 transfectants, alignment of these residues with the crystal structure of the CD11a I domain suggested that the IdeD epitope is located in close proximity to residues (Ile126 and Asn129) recently implicated in the ICAM-3 binding site. Interestingly, the IdeB and IdeC epitopes appeared to be in close proximity of a divalent cation binding pocket within the CD11a I domain that regulates both ICAM-1 and ICAM-3 adhesion. Taken together, these data indicate that distinct regions of the CD11a I domain contain epitopes for antibodies that either selectively inhibit binding of LFA-1 to ICAM-3, or interfere with both ICAM-1 and ICAM-3 binding of LFA-1.
Binnerts
M E
ME
Department of Tumor Immunology, University of Nijmegen, 6525 EX Nijmegen, The Netherlands.
van Kooyk
Y
Y
Edwards
C P
CP
Champe
M
M
Presta
L
L
Bodary
S C
SC
Figdor
C G
CG
Berman
P W
PW
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D000937:Antigen-Antibody Reactions; D015703:Antigens, CD; D000943:Antigens, Differentiation; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000276:immunology*; D004789:Enzyme Activation; D018604:Epitope Mapping; D006801:Humans; D016169:Lymphocyte Function-Associated Antigen-1 / Q000276:immunology*; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D015815:Cell Adhesion Molecules; C483616:ICAM3 protein, human; D016169:Lymphocyte Function-Associated Antigen-1