Induction of apoptotic cell death in peripheral blood mononuclear and polymorphonuclear cells by an oral bacterium, Fusobacterium nucleatum - PubMed (original) (raw)

Induction of apoptotic cell death in peripheral blood mononuclear and polymorphonuclear cells by an oral bacterium, Fusobacterium nucleatum

A Jewett et al. Infect Immun. 2000 Apr.

Abstract

It is largely unknown why a variety of bacteria present in the oral cavity are capable of establishing themselves in the periodontal pockets of nonimmunocompromised individuals in the presence of competent immune effector cells. In this paper we present evidence for the immunosuppressive role of Fusobacterium nucleatum, a gram-negative oral bacterium which plays an important role in the generation of periodontal disease. Our studies indicate that the immunosuppressive role of F. nucleatum is largely due to the ability of this organism to induce apoptotic cell death in peripheral blood mononuclear cells (PBMCs) and in polymorphonuclear cells (PMNs). F. nucleatum treatment induced apoptosis of PBMCs and PMNs as assessed by an increase in subdiploid DNA content determined by DNA fragmentation and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling assays. The ability of F. nucleatum to induce apoptosis was abolished by either heat treatment or proteinase digestion but was retained after formaldehyde treatment, suggesting that a heat-labile surface protein component is responsible for bacterium-mediated cell apoptosis. The data also indicated that F. nucleatum-induced cell apoptosis requires activation of caspases and is protected by NF-kappaB. Possible mechanisms of F. nucleatum's role in the pathogenesis of periodontal disease are discussed.

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Figures

FIG. 1

FIG. 1

Dose-dependent induction of apoptotic cell death of PBMCs by F. nucleatum. PBMCs were cocultured in the presence of F. nucleatum at the indicated ratios. The levels of apoptotic cell death were determined by using flow cytometric analysis of propidium iodide-stained cells.

FIG. 2

FIG. 2

Inhibition of _F. nucleatum_-mediated apoptotic cell death of PBMCs by the ICE inhibitor. Jurkat cells were cocultured in the presence of F. nucleatum and P. intermedia (30:1 bacterium-cell ratio) overnight. Equal amounts of DNA (2 μg) extracted from equal numbers of cells for each sample were loaded onto a 2% agarose gel and run on a gel electrophoresis assay. Lanes: 1, molecular weight marker; 2, untreated Jurkat cells; 3, Jurkat cells treated with viable P. intermedia; 4, Jurkat cells treated with viable F. nucleatum; 5, Jurkat cells treated with 1% formaldehyde-treated F. nucleatum; 6, Jurkat cells treated with viable F. nucleatum and 500 μM ICE inhibitor YVAD; 7, Jurkat cells treated with 1% formaldehyde-treated F. nucleatum and YVAD; 8, Jurkat cells treated with anti-FAS antibody; 9, Jurkat cells treated with Anti-FAS antibody and YVAD.

FIG. 3

FIG. 3

Inhibition of _F. nucleatum_-induced apoptotic cell death of PBMCs by pronase. F. nucleatum was cultured for 18 h in the presence or absence of pronase (10 mg/ml) (protease type XIV; EC 3.4.24.31) prior to its addition to Jurkat cells. The Jurkat cells were then cocultured for 18 h with either the pronase-treated F. nucleatum (+ Pronase) or control untreated F. nucleatum (− Pronase). Jurkat cell apoptosis was determined by flow cytometric analysis of propidium iodide-stained cells.

FIG. 4

FIG. 4

Induction of cell death in peripheral blood PMNs by F. nucleatum. PMNs at a concentration of 2 × 106 per ml were cocultured in the presence of F. nucleatum for 16 h. The numbers of viable cells were counted by trypan blue staining.

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