title: Properdin-Mediated C5a Production Enhances Stable Binding of Platelets to Granulocytes in Human Whole Blood.
abstract: Enhanced levels of platelet/granulocyte aggregates (PGAs) are found in patients suffering from many different inflammatory vascular diseases, and their formation in animal models of vascular disease is associated with increased thromboinflammation and worsened outcomes. The complement system, a part of the innate immune system, influences PGA formation, but the mechanisms for its effects are unknown. In this study, we have defined complement-mediated mechanisms that enhance PGA formation in human whole blood stimulated with thrombin receptor-activating peptide (TRAP) using ex vivo flow cytometry assays. We demonstrate that physiological properdin, a positive regulator of complement alternative pathway activity, increases PGA formation when added to TRAP-stimulated blood. All physiological properdin forms increase PGA formation, but properdin tetramers are the most efficient at increasing complement activity and PGA formation. Inhibition of endogenous properdin, either circulating in the blood or produced locally by leukocytes, impairs TRAP-mediated PGA formation to the same level as specific inhibition of either the alternative or classical pathway. Additionally, blocking the interaction of C5a with its cellular receptor prevents properdin-mediated increases in PGA formation. Adding either properdin tetramers or C5a to whole blood increases CD11b expression on granulocytes, and this increase is prevented by blockade of the C5a-C5a receptor axis. Finally, we demonstrate that the effects of properdin on PGA formation are tightly regulated by Factor H. Cumulatively, our data indicate that properdin enhances PGA formation via increased production of C5a, and that inhibition of properdin function has therapeutic potential to limit thromboinflammation in diseases characterized by increased PGA formation.
authors.affiliation: Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, Ohio.
authors.forename: Adam Z
authors.initials: AZ
authors.lastname: Blatt
authors.affiliation: Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, Ohio.
authors.forename: Gurpanna
authors.initials: G
authors.lastname: Saggu
authors.affiliation: Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, Ohio.
authors.forename: Koustubh V
authors.initials: KV
authors.lastname: Kulkarni
authors.affiliation: Department of Biomedical Sciences, Oakland University William Beaumont School of Medicine, Rochester, Michigan.
authors.forename: Claudio
authors.initials: C
authors.lastname: Cortes
authors.affiliation: Department of Medicine, University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Thurman
authors.affiliation: Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Daniel
authors.initials: D
authors.lastname: Ricklin
authors.affiliation: Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: John D
authors.initials: JD
authors.lastname: Lambris
authors.affiliation: Vector Molecular Biology Section, LMVR, National Institute of Allergy and Infectious Diseases, NIH, Rockville, Maryland.
authors.forename: Jesus G
authors.initials: JG
authors.lastname: Valenzuela
authors.affiliation: Department of Medical Microbiology and Immunology, University of Toledo College of Medicine and Life Sciences, Toledo, Ohio.
authors.forename: Viviana P
authors.initials: VP
authors.lastname: Ferreira
mesh_terms: D001665:Binding Sites; D001792:Blood Platelets / Q000166:cytology* / Q000276:immunology; D002449:Cell Aggregation; D015936:Complement C5a / Q000032:analysis / Q000096:biosynthesis* / Q000276:immunology; D006098:Granulocytes / Q000166:cytology* / Q000276:immunology; D006801:Humans; D011414:Properdin / Q000276:immunology* / Q000302:isolation & purification
chemical_list: D011414:Properdin; D015936:Complement C5a