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Induction of macrophage procoagulant activity by Bacteroides fragilis
G A Rosenthal1, G Levy, O D Rotstein
1Department of Surgery, Toronto General Hospital, Ontario, Canada.
Abstract:
Fibrin deposition in the peritoneal cavity during acute peritonitis appears to predispose the host to abscess formation by providing an environment for bacterial proliferation protected from host defenses. The purpose of the present study was to determine whether the potent abscess-inducing anaerobe Bacteroides fragilis could promote fibrin deposition by inducing mononuclear cells to express procoagulant activity (PCA). B. fragilis stimulated PCA in a dose-dependent fashion, achieving a maximum at 10(7) CFU/ml. Heat-killed B. fragilis induced comparable levels of PCA, while a nonspecific phagocytic stimulus, latex beads, was not stimulatory. B. fragilis was capable of inducing PCA even when phagocytosis was blocked by preexposure of cells to latex beads. The results suggested that phagocytosis was neither necessary nor sufficient for the generation of PCA. Cell separation studies showed that PCA was solely produced by macrophages and that lymphocytes did not augment its production. These studies suggest one potential mechanism by which B. fragilis might initiate abscess formation.
Insights
Bacteroides fragilis can trigger fibrin deposition, a key step in abscess formation during peritonitis. This occurs when macrophages express procoagulant activity (PCA) in response to the bacteria.
Area of Science:
- Microbiology
- Immunology
- Pathology
Background:
- Fibrin deposition in peritonitis creates a protected environment for bacterial growth, promoting abscess formation.
- The potent abscess-inducing anaerobe Bacteroides fragilis is implicated in this process.
Purpose of the Study:
- To investigate if Bacteroides fragilis induces mononuclear cells to express procoagulant activity (PCA).
- To elucidate the role of PCA in abscess formation initiated by B. fragilis.
Main Methods:
- Mononuclear cells were stimulated with varying concentrations of B. fragilis.
- Procoagulant activity (PCA) was measured.
- Phagocytosis was blocked using latex beads.
- Cell separation studies identified the cell types responsible for PCA production.
Main Results:
- B. fragilis dose-dependently stimulated PCA, with maximum activity at 10(7) CFU/ml.
- Heat-killed B. fragilis induced PCA, indicating a non-viable component is involved.
- Phagocytosis was not required for PCA generation.
- Macrophages, not lymphocytes, were the sole producers of PCA.
Conclusions:
- Bacteroides fragilis induces macrophages to express procoagulant activity (PCA).
- This PCA induction is independent of phagocytosis.
- This mechanism contributes to fibrin deposition and potential abscess formation in peritonitis.