The structural motif glycine 190-valine 202 of the fibrinogen gamma chain interacts with CD11b/CD18 integrin (alpha M beta 2, Mac-1) and promotes leukocyte adhesion.
The leukocyte-restricted integrin CD11b/CD18 (alpha M beta 2, Mac-1) is a receptor for fibrinogen on stimulated monocytes and neutrophils. At variance with platelet alpha IIb beta 3 or endothelial cell alpha v beta 3 integrins, CD11b/CD18 interacts with a approximately 30-kDa plasmic fragment D (D30) of fibrinogen that lacks the Arg-Gly-Asp sequences in the A alpha chain and the carboxyl terminus of the gamma chain. Using epitope-mapped antibodies and synthetic peptidyl mimicry, we have now identified a unique linear sequence in fibrinogen that mediates ligand binding to CD11b/CD18. Anti-fibrinogen antibodies directed to the gamma chain region 95-264 inhibited 125I-fibrinogen or 125I-D30 binding to chemoattractant-stimulated neutrophils or monocytic THP-1 cells in a dose-dependent fashion. Partially overlapping synthetic peptides reproducing this gamma chain region were tested for their ability to inhibit fibrinogen binding to leukocytes. A synthetic peptide designated P1, duplicating gamma chain Gly190-Val202, inhibited 125I-fibrinogen binding to stimulated neutrophils or THP-1 cells and blocked adhesion of these cells to immobilized fibrinogen in a dose-dependent fashion. Increasing concentrations of P1 inhibited 125I-fibrinogen binding to isolated CD11b/CD18 in a cell-free system. Consistent with genuine peptidyl mimicry, 125I-P1 bound saturably to THP-1 cells in a reaction inhibited by molar excess of unlabeled peptide, fibrinogen, or D30. Finally, immobilized P1 effectively supported adhesion of THP-1 cells in a CD11b/CD18-dependent manner. These data suggest that the fibrinogen gamma chain region Gly190-Val202 functions as a minimal recognition sequence for the leukocyte integrin CD11b/CD18. Given the participation of fibrinogen:leukocyte interaction in inflammation and atherogenesis, antagonists based on this unique structural motif would effectively interfere with aberrant leukocyte adhesion mechanisms without affecting Arg-Gly-Asp-directed vascular integrins.
Altieri
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DC
Committee on Vascular Biology, Scripps Research Institute, La Jolla, California 92037.
Plescia
J
J
Plow
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EF
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000378:metabolism*; D018845:CD11 Antigens; D018821:CD18 Antigens; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D005340:Fibrinogen / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D005998:Glycine / Q000737:chemistry; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D007962:Leukocytes / Q000502:physiology*; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008969:Molecular Sequence Data; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D014633:Valine / Q000737:chemistry
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018845:CD11 Antigens; D018821:CD18 Antigens; D016023:Integrins; D010446:Peptide Fragments; D009240:N-Formylmethionine Leucyl-Phenylalanine; D005340:Fibrinogen; D014633:Valine; D005998:Glycine