# Dietary antigens drive the generation of functional cytotoxic intraepithelial lymphocytes for early defense against foodborne pathogens

## TL;DR

Dietary antigens, not gut bacteria, are key for creating immune cells that protect against foodborne pathogens in the gut.

## Contribution

This study reveals dietary antigens, not gut microbiota, are essential for generating functional cytotoxic IELs in the small intestine.

## Key findings

- IELs are severely depleted and lose function in antigen-free mice.
- Dietary antigen-induced IELs provide rapid protection against Listeria monocytogenes.
- IL-12 from intestinal dendritic cells supports IEL maintenance and function.

## Abstract

Intraepithelial lymphocytes (IELs) constitute the largest lymphocyte population in the body and exhibit direct cytotoxic effector functions. Despite their abundance and importance in mucosal immunity, the mechanisms governing the generation and maintenance of functional IELs remain incompletely understood. Given the predominance of dietary components in the small intestine, dietary antigens may play a critical role in regulating the generation, maintenance, and functional maturation of IELs.

To assess the relative contributions of gut microbiota and dietary antigens to IEL development and function, we analyzed IEL populations in germ-free (GF) and antigen-free (AF) mice, which are GF mice fed with an amino acid diet lacking intact dietary proteins. IEL generation, persistence, and effector function were evaluated, along with the role of IL-12 in IEL function. Resistance of foodborne pathogen was examined using Listeria monocytogenes.

Conventional TCRαβ+ CD4+ and CD8+ IEL populations are present in normal numbers in germ-free (GF) mice which lack microbiota. However, these IELs are severely depleted in AF mice, and the few remaining IELs in AF mice lack effector functions. Notably, while TCRαβ+ CD8αβ+ IELs in adult GF mice can persist for prolonged periods, they lose their effector function when fed with an AF diet. IL-12 presumably produced by intestinal dendritic cells plays a critical role in the maintenance of TCRαβ+ CD8αβ+ IELs and their effector functions. Importantly, mice lacking functional dietary antigen-induced TCRαβ+ CD8αβ+ IELs showed impaired early protection against oral infection with L. monocytogenes.

Collectively, these findings demonstrate that dietary antigens rather than gut microbiota, are critical for the generation of innate-like cytotoxic IELs in the small intestine. Dietary antigen-driven TCRαβ+ CD8αβ+ IELs provide rapid and local immune protection against foodborne-pathogens, highlighting a previously underappreciated role of dietary antigens in shaping intestinal immune defense.