# Regulation of allergies across the body by microbial metabolites

## TL;DR

This review explains how gut bacteria and their metabolites influence allergies by regulating the immune system and suggests that improving gut health could help prevent or treat allergic diseases.

## Contribution

The paper systematically reviews the role of microbial metabolites in regulating allergic immune responses and identifies key metabolites for therapeutic potential.

## Key findings

- Individuals prone to allergies often have less diverse gut bacteria and altered microbial metabolite levels.
- Short-chain fatty acids and other microbial metabolites can regulate immune cells and reduce inflammation.
- Promoting gut health through diet and probiotics may help manage allergic diseases.

## Abstract

Allergies are adverse immune responses to typically harmless substances, known as allergens. While allergies can involve diverse immune responses, type 2 immune responses that induce acute hypersensitivity mediated by mast cells, eosinophils and basophils are the major mechanisms underlying allergic disorders. Allergic diseases include atopic dermatitis, allergic rhinitis, food allergies and asthma. The onset and persistence of allergic disorders are influenced by genetic factors, pre-existing illnesses, age, environmental conditions and other lifestyle factors. In particular, diet and microbiomes considerably affect the incidence of various allergic diseases in the skin, lung and intestine. Individuals prone to develop allergic diseases often have impaired and skewed microbial diversification over the first year of life, and this can lead to altered levels of microbial metabolites in the intestine and inflamed tissues. Microbial metabolites, such as short-chain fatty acids, indole metabolites and bile acids, can exert specific regulatory effects on the various components of the immune system, such as barrier epithelial cells and immune cells, including dendritic cells, macrophages, T cells, B cells, innate lymphoid cells and mast cells. Microbial metabolites can also promote immune tolerance to allergenic substances by strengthening regulatory T cells. Understanding the role of these metabolites can lead to better prevention and control of allergic diseases. Here, in this review, we examine current research progress on the interactive relationship between microbial metabolites and allergic diseases and identify functionally important metabolites that affect allergic immune responses.

Allergies, such as hay fever and asthma, are common and can be severe. They often result from the body’s reaction to harmless substances such as pollen or certain foods. This Review explores how gut bacteria and their metabolites influence allergies. Researchers found that people with allergies often have less diverse gut bacteria. This imbalance, known as dysbiosis, can lead to fewer beneficial metabolites such as short-chain fatty acids (SCFAs), which help regulate the immune system. The study reviewed various experiments and clinical data to understand how these microbial metabolites affect allergies. SCFAs, for example, can strengthen the gut lining and reduce inflammation, potentially lowering allergy risks. The research also highlighted the role of other metabolites in managing immune responses. The findings suggest that improving gut health and the immune system through diet,probiotics, and postbiotics might help prevent or treat allergies.

This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.