PMNs' role on clearance of E. faecalis from oral cavity

Abstract

Objectives: The goal of this study was to measure 1) the ability of polymorphonuclear neutrophils (PMNs) leukocytes to kill oral Enterococcus faecalis strains, 2) upregulation of inflammatory mediators by PMNs cells in interaction with E. faecalis, and 3) the ability of E. faecalis to cause inflammation in mouse muscle tissue. Methods: Fifteen endodontic and nine salivary strains of E. faecalis were isolated and identified by specific 16S-rRNA primers. The bacteria were grown in BHI broth and incubated with mouse PMN cells in appropriate media to determine the ability of the PMNs cells to kill the bacteria. In other experiments upregulation of IL-1á, TNF-á, MMP-8 and COX-2 mRNA by the PMNs was measured after exposure of the leukocytes to the bacteria using real time PCR. Finally, the inflammatory potential of and PMN response to E. faecalis suspension in mouse muscle tissue was examined from histological sections using hematoxylin-eosin and immunostaining. Results: Murine PMNs killed about 80% of the E. faecalis cells in one hour, irrespective of the source of isolation of the strains. Quantitative PCR results showed that IL-1á, TNF-á, MMP-8 and COX-2 mRNA were markedly up-regulated in E. faecalis-stimulated PMNs or in E. faecalis-invaded muscular tissues. MMP-8 mRNA level was positively related to COX-2 mRNA level. Histological evaluation and immunostaining disclosed that all E. faecalis strains could recruit PMNs to the local infectious sites and cause abscess formation. Conclusions: E. faecalis strains from saliva and infected root canals have the potential to recruit PMNs in the infectious sites leading to inflammation via up-regulation of PMN IL-1á, TNF-á, MMP-8 and COX-2. PMNs cells can also play a role in killing of E. faecalis.