title: Complement C3dg-mediated erythrophagocytosis: implications for paroxysmal nocturnal hemoglobinuria.
abstract: The clinical management of paroxysmal nocturnal hemoglobinuria (PNH), a rare but life-threatening hematologic disease, has fundamentally improved with the introduction of a therapeutic that prevents complement-mediated intravascular hemolysis. However, a considerable fraction of PNH patients show insufficient treatment response and remain transfusion dependent. Because the current treatment only prevents C5-induced lysis but not upstream C3 activation, it has been speculated that ongoing opsonization with C3 fragments leads to recognition and phagocytosis of PNH erythrocytes by immune cells. Here, for the first time, we provide experimental evidence for such extravascular hemolysis and demonstrate that PNH erythrocytes from anti-C5-treated patients are phagocytosed by activated monocytes in vitro. Importantly, we show that this uptake can be mediated by the end-stage opsonin C3dg, which is not traditionally considered a phagocytic marker, via interaction with complement receptor 3 (CR3). Interaction studies confirmed that C3dg itself can act as a ligand for the binding domain of CR3. The degree of C3dg-mediated erythrophagocytosis in samples from different PNH patients correlated well with the individual level of C3dg opsonization. This finding may guide future treatment options for PNH but also has potential implications for the description and management of other complement-mediated diseases.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA;
authors.forename: Zhuoer
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA; Institute of Pharmacology of Natural Products and Clinical Pharmacology, Ulm University, Ulm, Germany; and.
authors.forename: Christoph Q
authors.initials: CQ
authors.lastname: Schmidt
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA;
authors.forename: Sophia
authors.initials: S
authors.lastname: Koutsogiannaki
authors.affiliation: Hematology, Department of Clinical Medicine and Surgery, Federico II University of Naples, Naples, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Ricci
authors.affiliation: Hematology, Department of Clinical Medicine and Surgery, Federico II University of Naples, Naples, Italy.
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Risitano
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA;
authors.forename: John D
authors.identifier: http://orcid.org/0000-0002-9370-5776
authors.initials: JD
authors.lastname: Lambris
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA;
authors.forename: Daniel
authors.identifier: http://orcid.org/0000-0001-6140-0233
authors.initials: D
authors.lastname: Ricklin
mesh_terms: D003179:Complement C3b; D004912:Erythrocytes / Q000276:immunology / Q000473:pathology; D006457:Hemoglobinuria, Paroxysmal / Q000097:blood* / Q000276:immunology*; D006461:Hemolysis / Q000276:immunology; D006801:Humans; D016177:Macrophage-1 Antigen / Q000097:blood; D018448:Models, Immunological; D009895:Opsonin Proteins / Q000097:blood; D010446:Peptide Fragments / Q000097:blood*; D010587:Phagocytosis / Q000276:immunology
chemical_list: D016177:Macrophage-1 Antigen; D009895:Opsonin Proteins; D010446:Peptide Fragments; C045477:complement C3d,g; D003179:Complement C3b