title: Neisseria meningitidis and Escherichia coli are protected from leukocyte phagocytosis by binding to erythrocyte complement receptor 1 in human blood.
abstract: The initial interaction of Gram-negative bacteria with erythrocytes and its implications on leukocyte phagocytosis and oxidative burst in human whole blood were examined. Alexa-labeled Escherichia coli, wild-type H44/76 N. meningitidis and the H44/76lpxA lipopolysaccharide (LPS)-deficient mutant were incubated with whole blood using lepirudin as anticoagulant which has no adverse effects on complement. Bacteria free in plasma, bound to erythrocytes or phagocytized by granulocytes and monocytes were quantified using flow cytometry. The effects of the C3 inhibitor compstatin, a C5a receptor antagonist (C5aRa) and a complement receptor 1 (CR1)-blocking antibody (3D9) were examined. Most bacteria (80%) immediately bound to erythrocytes. The binding gradually declined over time, with a parallel increase in phagocytosis. Complement inhibition with compstatin reduced erythrocyte binding and bacterial C3 opsonization. In contrast, the C5aRa efficiently reduced phagocytosis, but did not affect the binding of bacteria to erythrocytes. The anti-CR1 blocking mAb dose-dependently reduced bacterial binding to erythrocytes to nil, with subsequent increased phagocytosis and oxidative burst. LPS had no effect on these processes since similar results were obtained using an LPS-deficient N. meningitidis mutant. In vivo experiments in a pig model of sepsis showed limited binding of bacteria to erythrocytes, consistent with the facts that erythrocyte CR1 receptors are absent in non-primates and that the bacteria were mainly found in the lungs. In conclusion, complement-dependent binding of Gram-negative bacteria to erythrocyte CR1 decreases phagocytosis and oxidative burst by leukocytes in human whole blood.
authors.affiliation: Department of Laboratory Medicine, Nordland Hospital, Bodø, Norway; Institute of Medical Biology, University of Tromsø, Tromsø, Norway. ole.lars.brekke@nlsh.no
authors.forename: Ole-Lars
authors.initials: OL
authors.lastname: Brekke
authors.forename: Bernt Christian
authors.initials: BC
authors.lastname: Hellerud
authors.forename: Dorte
authors.initials: D
authors.lastname: Christiansen
authors.forename: Hilde
authors.initials: H
authors.lastname: Fure
authors.forename: Albert
authors.initials: A
authors.lastname: Castellheim
authors.forename: Erik Waage
authors.initials: EW
authors.lastname: Nielsen
authors.forename: Anne
authors.initials: A
authors.lastname: Pharo
authors.forename: Julie Katrine
authors.initials: JK
authors.lastname: Lindstad
authors.forename: Grethe
authors.initials: G
authors.lastname: Bergseth
authors.forename: Graham
authors.initials: G
authors.lastname: Leslie
authors.forename: John D
authors.initials: JD
authors.lastname: Lambris
authors.forename: Petter
authors.initials: P
authors.lastname: Brandtzaeg
authors.forename: Tom Eirik
authors.initials: TE
authors.lastname: Mollnes
mesh_terms: D000818:Animals; D002469:Cell Separation; D003165:Complement System Proteins; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D004912:Erythrocytes / Q000276:immunology* / Q000378:metabolism; D004926:Escherichia coli / Q000276:immunology / Q000378:metabolism; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D016905:Gram-Negative Bacterial Infections / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007962:Leukocytes / Q000276:immunology* / Q000378:metabolism; D009345:Neisseria meningitidis / Q000276:immunology / Q000378:metabolism; D010587:Phagocytosis / Q000276:immunology*; D017463:Receptors, Complement 3b / Q000378:metabolism*; D016897:Respiratory Burst; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018805:Sepsis / Q000276:immunology / Q000378:metabolism; D013552:Swine
chemical_list: C509991:CR1 protein, human; D017463:Receptors, Complement 3b; D003165:Complement System Proteins