Infant intestinal Enterococcus faecalis down-regulates inflammatory responses in human intestinal cell lines

Area of Science:

• Microbiology
• Immunology
• Gastroenterology

Background:

• Intestinal inflammation is a significant health concern.
• Lactic acid bacteria (LAB) are known for their potential health benefits, including immune modulation.
• Understanding the specific mechanisms by which LAB interact with the host immune system is crucial.

Purpose of the Study:

• To investigate the immunomodulatory capacity of various Lactic acid bacteria (LAB) strains on human intestinal cell lines.
• To identify specific LAB strains and their components responsible for regulating inflammatory responses.
• To explore the role of Toll-like receptors (TLRs) in LAB-mediated immune modulation.

Main Methods:

• Treatment of human intestinal cell lines (Caco-2, HT-29, HCT116) with different LAB strains.
• Quantification of IL-8 and TGF-beta protein secretion using ELISA.
• Assessment of cytokine and Toll-like receptor (TLR) gene expression via RT-PCR.
• Analysis of bacterial components (conditional medium, sonicated, UV-killed bacteria) and surface molecules (carbohydrates, proteins) for their effects.
• Adhesion assays to evaluate bacterial interaction with intestinal cells.

Main Results:

• Enterococcus faecalis demonstrated significant immunomodulatory effects, downregulating IL-8 and upregulating TGF-beta secretion.
• The observed immunomodulation was strain-specific, with only a subset of tested E. faecalis strains showing this effect.
• E. faecalis appears to modulate inflammatory responses through TLR3, TLR4, TLR9, and TRAF6 pathways.
• Bacterial cell surface carbohydrates were identified as key factors in both adhesion and immune regulation.

Conclusions:

• Specific strains of E. faecalis possess a unique ability to modulate intestinal mucosal immunity.
• These findings highlight the strain-dependent nature of LAB's immunomodulatory effects.
• E. faecalis may play a role in maintaining colonic homeostasis and regulating inflammatory responses through its surface carbohydrates and interaction with TLRs.