title: Fc-binding components: a virulence factor in Actinobacillus actinomycetemcomitans?
abstract: Actinobacillus actinomycetemcomitans (ATCC 33384) can produce and release components that bind to the Fc part of IgG. Fc-binding components were observed in whole bacteria, capsular material and medium from broth cultures. The components were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotted with biotinylated Fc-fragments and myeloma proteins. In a phagocytosis assay with human granulocytes and sheep erythrocytes, preincubation of opsonized erythrocytes with protein A reduced phagocytosis by 90%. In contrast, preincubation of the opsonizing antibody with medium components from a culture of A. actinomycetemcomitans enhanced the opsonizing effect of the antibody. The enhanced binding of erythrocytes may be caused by formation of aggregates between opsonizing antibody and bacterial Fc-binding components. Aggregated IgG can bind to low-affinity Fc gamma II and gamma III receptors that cannot bind monomeric IgG. Release of Fc-binding components from bacteria may contribute to the periodontal lesion through interference with the phagocytic activity of granulocytes and with the complement system. Fc-binding components may also interfere with downregulation of the B-cell response.
authors.affiliation: Institute of Microbiology, University of Oslo, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Tolo
authors.forename: K
authors.initials: K
authors.lastname: Helgeland
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000276:immunology* / Q000472:pathogenicity; D000907:Antibodies, Bacterial / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology*; D004591:Electrophoresis, Polyacrylamide Gel; D006098:Granulocytes / Q000276:immunology; D006801:Humans; D015151:Immunoblotting; D007141:Immunoglobulin Fc Fragments / Q000276:immunology*; D007074:Immunoglobulin G / Q000276:immunology; D009895:Opsonin Proteins / Q000276:immunology; D010518:Periodontitis / Q000276:immunology / Q000382:microbiology; D010587:Phagocytosis / Q000276:immunology*; D011485:Protein Binding; D011961:Receptors, Fc / Q000276:immunology*; D014774:Virulence
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D009895:Opsonin Proteins; D011961:Receptors, Fc