A key role of dendritic cells in probiotic functionality.

Area of Science:

• Immunology
• Microbiology
• Gastroenterology

Background:

• Intestinal homeostasis disruption and loss of tolerance to microbiota are key in inflammatory bowel disease (IBD).
• Probiotics, unlike pathogenic bacteria, can reduce inflammation.
• Dendritic cells (DCs) are crucial for immune regulation and tolerance induction.

Purpose of the Study:

• To investigate the role of dendritic cells (DCs) in mediating the anti-inflammatory effects of probiotic lactic acid bacteria (LAB).
• To explore the mechanisms by which probiotics interact with DCs to modulate immune responses.

Main Methods:

• Selected LAB strains were incubated with DCs in vitro.
• Probiotic-treated DCs were transferred to mice to assess protection against 2, 4, 6-trinitrobenzenesulfonic acid (TNBS)-induced colitis.
• Analysis of inflammatory markers, gene expression (including indoleamine 2,3-dioxygenase [IDO]), and immune cell populations (CD4+ CD25+ regulatory cells) was performed.
• Involvement of signaling pathways (MyD88, TLR2, NOD2) and cytokines (IL-10) was investigated.

Main Results:

• Probiotic LAB induced partial maturation of DCs in vitro.
• Transfer of probiotic-treated DCs significantly protected against TNBS-induced colitis, reducing inflammation and pro-inflammatory gene expression.
• Protection was linked to increased local IDO expression and required MyD88-, TLR2-, and NOD2-dependent signaling.
• Induction of CD4+ CD25+ regulatory cells occurred via an IL-10-independent pathway.

Conclusions:

• Selected probiotics can enhance DC regulatory functions through specific pattern-recognition receptors and signaling pathways.
• DCs play a significant role in mediating the immune interactions of probiotics.
• These findings suggest a potential therapeutic role for probiotic-modulated DCs in treating IBD.