Microbial Metabolites in Allergic Diseases: Beyond Short-Chain Fatty Acids

Area of Science:

• Microbiology
• Immunology
• Metabolomics

Background:

• The gut microbiota plays a crucial role in host homeostasis by producing bioactive metabolites.
• Short-chain fatty acids (SCFA) are well-known microbial metabolites linked to allergic diseases.
• Other microbial metabolites also significantly influence immune and inflammatory responses.

Purpose of the Study:

• To review microbial metabolites beyond SCFA involved in immune regulation.
• To explore the role of branched SCFA (BCFA), tryptophan and tyrosine derivatives, secondary bile acids (BA), sphingolipids (SL), histamine, polyamines, and odd-chain fatty acid (OCFA)-containing metabolites in immunity.
• To highlight their potential in managing allergic diseases.

Main Methods:

• Literature review of studies on gut microbial metabolites and immune function.
• Analysis of research linking specific metabolites to immune cell populations and inflammatory pathways.
• Synthesis of findings on the role of non-SCFA metabolites in allergic diseases.

Main Results:

• Branched SCFA (BCFA) contribute to allergic resolution and tolerance.
• Microbial tryptophan derivatives (e.g., indole-3-acetic acid) modulate T helper 17 (Th17) and regulatory T cells.
• Secondary bile acids (e.g., isolithocholic acid) inhibit Th17 responses, and sphingolipids maintain epithelial integrity.
• Alterations in polyamine and OCFA metabolism are observed in allergic diseases.

Conclusions:

• Gut microbial metabolites, beyond SCFA, are critical regulators of host immune responses.
• These metabolites, including BCFA, indole derivatives, and secondary BA, show promise in modulating allergic inflammation.
• Targeting microbial metabolism presents a potential avenue for personalized therapeutic strategies in allergic conditions.