title: Ig-like transcript 4 as a cellular receptor for soluble complement fragment C4d.
abstract: Complement regulation leads to the generation of complement split products (CSPs) such as complement component (C)4d, a marker for disease activity in autoimmune syndromes or antibody-mediated allograft rejection. However, the physiologic role of C4d has been unknown. By screening murine thymoma BW5147 cells expressing a cDNA library generated from human monocyte-derived dendritic cells with recombinant human C4d, we identified Ig-like transcript (ILT)4 and ILT5v2 as cellular receptors for C4d. Both receptors, expressed on monocytes, macrophages, and dendritic cells, also interacted with the CSPs C3d, C4b, C3b, and iC3b. However, C4d did not bind to classic complement receptors (CRs). Interaction between cell surface-resident ILT4 and soluble monomeric C4d resulted in endocytosis of C4d. Surprisingly, binding of soluble ILT4 to C4d covalently immobilized to a cellular surface following classic complement activation could not be detected. Remarkably, C4d immobilized to a solid phaseviaits intrinsic thioester conferred a dose-dependent inhibition of TNF-α and IL-6 secretion in monocytes activatedviaFc-cross-linking of up to 50% as compared to baseline. Similarly, C4d conferred an attenuation of intracellular Ca(2+)flux in monocytes activatedviaFc-cross-linking. In conclusion, ILT4 represents a scavenger-type endocytotic CR for soluble monomeric C4d, whereas attenuation of monocyte activation by physiologically oriented C4d on a surface appears to be dependent on a yet to be identified C4d receptor.-Hofer, J., Forster, F., Isenman, D. E., Wahrmann, M., Leitner, J., Hölzl, M. A., Kovarik, J. K., Stockinger, H., Böhmig, G. A., Steinberger, P., Zlabinger, G. J. Ig-like transcript 4 as a cellular receptor for soluble complement fragment C4d.
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Johannes
authors.initials: J
authors.lastname: Hofer
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Florian
authors.initials: F
authors.lastname: Forster
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: David E
authors.initials: DE
authors.lastname: Isenman
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Markus
authors.initials: M
authors.lastname: Wahrmann
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Judith
authors.initials: J
authors.lastname: Leitner
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Markus A
authors.initials: MA
authors.lastname: Hölzl
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Johannes J
authors.initials: JJ
authors.lastname: Kovarik
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Hannes
authors.initials: H
authors.lastname: Stockinger
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Georg A
authors.initials: GA
authors.lastname: Böhmig
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada peter.steinberger@meduniwien.ac.at gerhard.zlabinger@meduniwien.ac.at.
authors.forename: Peter
authors.initials: P
authors.lastname: Steinberger
authors.affiliation: *Division of Clinical Experimental Immunology and Division of Immune Receptors and T Cell Activation, Institute of Immunology, Molecular Immunology Unit, Institute for Hygiene and Applied Immunology, Centre for Pathophysiology, Infectiology, and Immunology, and Division of Nephrology and Dialysis, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria; and Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada peter.steinberger@meduniwien.ac.at gerhard.zlabinger@meduniwien.ac.at.
authors.forename: Gerhard J
authors.initials: GJ
authors.lastname: Zlabinger
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D003179:Complement C3b / Q000378:metabolism; D015933:Complement C3d / Q000378:metabolism; D015935:Complement C4b / Q000378:metabolism*; D003713:Dendritic Cells / Q000378:metabolism; D004705:Endocytosis; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D015850:Interleukin-6 / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D009000:Monocytes / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism*; D011485:Protein Binding; D011951:Receptors, Complement / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D015850:Interleukin-6; C491341:LILRB2 protein, human; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D011951:Receptors, Complement; D011971:Receptors, Immunologic; D014409:Tumor Necrosis Factor-alpha; D003179:Complement C3b; D015933:Complement C3d; D015935:Complement C4b; C032261:complement C4d; D002118:Calcium
keywords: antibody-mediated rejection; autoimmunity; complement receptor; homeostasis; scavenger receptor