Abstract
The aim of this study was to clarify the phagocytic mechanisms of a heat-killed cell preparation of Enterococcus faecalis strain EC-12 (EC-12) by antigen-presenting cells (APCs). Fluorescein isothiocyanate (FITC)-labeled EC-12 was cocultured with peritoneal macrophage and the amount of EC-12 phagocytosed by peritoneal macrophages was measured using a microplate fluorometer. Peritoneal macrophages from toll-like receptor (TLR)2-, TLR7-, and MyD88-deficient knockout (KO) mice exhibited similar levels of EC-12 phagocytosis to those from wild-type mice. Similarly, dectin-1 neutralization of peritoneal macrophages had no effect on EC-12 phagocytosis. However, blockade of the mannose receptor (MR) significantly decreased the amount of EC-12 phagocytosed by peritoneal macrophages; the same effect was observed in bone marrow-derived macrophages and dendritic cells. Our findings suggest that MR plays a major role in EC-12 phagocytosis by the APCs.This aim of this study was to clarify the phagocytic mechanisms of a heat-killed cell preparation of Enterococcus faecalis strain EC-12 (EC-12) by antigen-presenting cells (APCs). Our findings suggest that mannose receptor (MR) plays a major role in EC-12 phagocytosis by the APCs.
Highlights
Lactic acid bacteria (LAB) are regarded as symbiotic microorganisms that confer beneficial effects, such as preventing tumor development, limiting allergic reactions, and fighting infection (Reid et al 1990; Cross et al 2001; Asahara et al 2004; Lee et al 2004; Inoue et al 2007)
While the mechanism of phagocytosis of pathogenic microorganisms by antigenpresenting cells (APCs) has been well clarified, few studies have assessed the type of receptors involved in LAB phagocytosis
In experiment 1, we examined the role of TLR2, TLR7, and MyD88 in EC-12 phagocytosis by peritoneal macrophages
Summary
Lactic acid bacteria (LAB) are regarded as symbiotic microorganisms that confer beneficial effects, such as preventing tumor development, limiting allergic reactions, and fighting infection (Reid et al 1990; Cross et al 2001; Asahara et al 2004; Lee et al 2004; Inoue et al 2007). Our previous study demonstrated that nucleic acids, especially RNA, from heat-killed cell preparations of Enterococcus faecalis strain EC-12 (EC-12) induced IL-12 production by the murine macrophage-like cell line J774.1. This effect was mediated by toll-like receptor (TLR) 7 (Inoue et al 2011). Because TLR7 is expressed in endosomes but not cell membranes, EC-12 phagocytosis by APCs is an important event for the initiation of probiotic-like effects derived by EC-12 (Kuramoto et al 2004; Tsuruta et al 2009; Yoshikawa et al 2009)
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