Oral Microbiol Imtntmol 1991: 6: 'il2 aetinomycetemcomitans produces simi-

% active celis

50 -

40

In iig/ml A. aetinomycetemcomitans

Fig. 4. Rabbit antiserum to sheep erythrocytes was incubated for 30 min with components recovered from the medium of a culture of A. aetinomyeetemeomitans. Sheep erythrocytes were added and the suspension was incubated for 1 h at 37°C, washed and incubated with human granulocytes. The medium was withdrawn and the granulocytes were washed, fixed and examined in phase-contrast microscopy.

components may engage a large number of gamme II and gamma III Fc receptors on the granulocytes and also bind to the erythrocytes by the Fab activity. This mechanism might explain the observation of an increased proportion of phagocytically active cells. Aggregates of IgG contribute to cross-linking of Fc gamma II and gamma i n receptors of B-suppressor cells and are considered to trigger downregulation of B-cell proliferation and the humoral immune response (10). In periodontitis, bacterial Fc-binding components may interfere with the

downregulation by blocking the Fc of the aggregating IgG. Such blocking may contribute to the proliferation of B-cells observed in association with the periodontal lesions. Leukotoxin from A. aetinomyeetemeomitans is recognized for its selective killing of cells of the myelomonoeytic cell line (1, 24, 27). Leukocidal activity was recently also observed in Staphyloeoeeus aureus that produces protein A but not in 6 other staphylococci strains negative for Fc-binding components. (18). The apparent association between Fc-binding components and leukocidal

lar components, binding of aggregated components to C3R may have occurredi The Fc receptors in Haemophilus somnus are nonimmunogenic (6, 7), and all isolates of H. somnus recovered fron? cattle with disease syndromes displayed Fc receptors (30), indicating that Fc rdr ceptors constitute a virulence factor m such infections. This may also be the case in periodontal lesions infected with A. aetinomycetemcomitans or other bacteria capable of releasing Fc-binding components. DNA fragments coding for Fc-binding components can be transferred by plasmids (3). The effect of interactions between IgG, bacterial Fc-binding components and phagocytic cells on clearing of bacteria probably depends on the relative proportions of the reactants. In the periodontal lesion the concentration of bacterial Fc-binding components may reach concentrations that contribute to the progression of periodontitis. Viable A. aetinomyeetemeomitans has been recovered from biopsies in juvenile periodontitis (5) and from circulating blood in patients with pericarditis (11), indicating that the bacterium resists the bactericidal activity of serum. Transmission electron microscopy of human epithelial cells cocultured with A. actinomycetem-

Fc-binding components and Aetinobacillus actinomycetemcomitans

377

tors influencing neutrophil defects in 22, Potts TV, Zambon JJ, Genco RJ. Reasperiodontal disease, J Dent Res 1986: 65: signment of Aetinobaeillus aetinomyeet1379-1391, emeomitans to the genus Hemophilus as Hemophiius aetinomyeetemeomitans. Int 10, Heyman B. The immune complex: possJ Syst Bacteriol 1985: 35: 337-341, ible ways of regulating the antibody response. Immunol Today 1990: 11: 23, Schalen CT, Lennart T, Christensen KK, 10-312, Christensen P, Blocking of antibody 11, Horowitz EA, Pugsley MP, Turbes PG, complement-dependent effector funcClark RB. Pericarditis caused by Aetinotions by streptococcal IgG Fc-receptor and staphylococcal protein A, Acta Pabaeillus aetinomveetemeomitans. J Infect thol Microbiol Scand [B] 1985: 93: Dis 1987: 155: 152-153, 395-400. 12, Humphrey JD, Stephens LR, HemophiReferences lus somnus: a review. Vet Bull 1983: 53: 24, Simpson DL, Berthold P, Taichman NS. Killing of human myelomonoeytic leuke987-1004, 1, Baehmi P, Tsai CC, McArthur WP, mia and lymphocytic cell lines by Aetino13, Kaplan AH, Weber DJ, Oddone EZ, Hammond BF, Taichman NS. Interacbaeillus aetinomyeetemeomitans. Infect Perfect JR. Infection due to Aetinotion of inflammatory cellp and oral Immun 1988: 56: 1162-1166, baeiilus aetinomyeetemeomitans. 15 cases microorganisms. VIII. Detection of leu25, Sundqvist G, Johansson E, Bactericidal and review. Rev Infect Dis 1989: 11: kocytic activity of a plaque-derived effect of pooled human serum on Bacter46-63, gram-negative microorganism. Infect oides melaninogenieus, Baeteroides asae14, Kronwall G, A surface component in Immun 1979: 24; 233-243, eharolytieus and Aetinobaeillus aetinogroup A, C and G streptococci with non2, Blackwell JH, Ezekowitz RA, Roberts myeetemeomitans. Scand J Dent Res immune reactivity for immunoglobulin MB, Channon JY, Sims RB, Gordon S, 1982: 90: 29-36, G, J Immunol 1973: 111: I401-I406. 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Infect Immun 1984: 43: 157-252. factor and IgG and IgA Fc-receptors. 700-705, 17, Lederer JA, Brown JF, Czuprynski CJ, Acta Pathol Scand [B] 1983: 91: 61-67. 28, von Mering GO, Boyle MDR Compari"Hemophilus somnus": a facultative in4, Bayum A. Separation of blood leukoson of type III Fc receptors associated tracellular pathogen of bovine monocytes, granulocytes and lymphocytes. with group C and group G streptococci, nuclear phagocytes. Infect Immun 1987: Tissue Antigens 1974: 4: 269-274. Mol Immunol 1986: 23: 811-821. 55: 381-387. 5, Christersson LA, VikesJ0 UME, Albini 29, Widders PR, Smith JW, Yarnall M, 18, Masayasu I, Slots J, Berthold P, TaichB, Zambon JJ, Genco RJ, Tissue localizMcGuire TC, Corbeil LB, Non-immune man NS. Leukocidial activity of staphylation of Aetinobaeillus aetinomyeetemeoimmunoglobulin binding by Hemopitiius ococci isolated from human periodontal mitans in human periodontitis, J Periosomnus. J Med Microbiol 1988: 26: lesions. 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comitans in our laboratory showed morphologically intact bacteria in the human cells (Schlytte Blix et al, in preparation). In conclusion, release of Fcbinding components from bacteria may interfere with the phagocytic activity, complement function and downregulation of B-cell proliferation in the periodontal infiltrates.

Fc-binding components: a virulence factor in Actinobacillus actinomycetemcomitans?

Actinobacillus actinomycetemcomitans (ATCC 33384) can produce and release components that bind to the Fc part of IgG. Fc-binding components were obser...
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