IgM and stromal cell-associated heparan sulfate/heparin as complement-independent ligands for CD19.
The more severe phenotype of mice lacking CD19 as compared to CD21 suggests that a complement-independent ligand for the CD19/CD21 complex exists. We sought ligands for CD19 by examining binding reactions with fusion proteins comprised of the extracellular region of CD19 and the Fc region of IgG1. A fusion protein containing the third extracellular domain (D3-Fc) bound to WEHI-231 cells, and this was competed by soluble IgM. This function of IgM was confirmed by the binding of D3-Fc to beads coated with IgM. A second ligand for D3-Fc was found on stromal cells, and was shown to be heparin/heparan sulfate. These two ligands would be considered to reside on follicular dendritic cells, and may account for the observed ability of D3-Fc to bind to sites in germinal centers containing these cells.
de Fougerolles
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AR
Wellcome Trust Immunology Unit, Department of Medicine, University of Cambridge School of Clinical Medicine, Cambridge, GB, UK.
Batista
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F
Johnsson
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Fearon
D T
DT
D000818:Animals; D018941:Antigens, CD19 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D003165:Complement System Proteins / Q000276:immunology; D003713:Dendritic Cells / Q000276:immunology; D018858:Germinal Center / Q000276:immunology; D006493:Heparin / Q000378:metabolism*; D006497:Heparan Sulfate / Q000378:metabolism*; D007074:Immunoglobulin G / Q000235:genetics; D007075:Immunoglobulin M / Q000276:immunology*; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017154:Stromal Cells / Q000737:chemistry / Q000276:immunology*
D018941:Antigens, CD19; D003165:Complement System Proteins; D006493:Heparin; D006497:Heparan Sulfate; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D008024:Ligands; D011993:Recombinant Fusion Proteins