T-cell derived acetylcholine aids host defenses during enteric bacterial infection with Citrobacter rodentium.

Valerie T Ramirez,Diane Tu,Patricia A Castillo,Mariana Barboza Gardner,Charles L Bevins,Jessica A Sladek,Melanie G Gareau,Eric B Nonnecke,Ingrid Brust-Mascher,Colin Reardon,Dayn R Godinez,Carlito B Lebrilla,Elaine N Miller,Dana J Philpott

doi:10.1371/journal.ppat.1007719

Abstract

The regulation of mucosal immune function is critical to host protection from enteric pathogens but is incompletely understood. The nervous system and the neurotransmitter acetylcholine play an integral part in host defense against enteric bacterial pathogens. Here we report that acetylcholine producing-T-cells, as a non-neuronal source of ACh, were recruited to the colon during infection with the mouse pathogen Citrobacter rodentium. These ChAT+ T-cells did not exclusively belong to one Th subset and were able to produce IFNγ, IL-17A and IL-22. To interrogate the possible protective effect of acetylcholine released from these cells during enteric infection, T-cells were rendered deficient in their ability to produce acetylcholine through a conditional gene knockout approach. Significantly increased C. rodentium burden was observed in the colon from conditional KO (cKO) compared to WT mice at 10 days post-infection. This increased bacterial burden in cKO mice was associated with increased expression of the cytokines IL-1β, IL-6, and TNFα, but without significant changes in T-cell and ILC associated IL-17A, IL-22, and IFNγ, or epithelial expression of antimicrobial peptides, compared to WT mice. Despite the increased expression of pro-inflammatory cytokines during C. rodentium infection, inducible nitric oxide synthase (Nos2) expression was significantly reduced in intestinal epithelial cells of ChAT T-cell cKO mice 10 days post-infection. Additionally, a cholinergic agonist enhanced IFNγ-induced Nos2 expression in intestinal epithelial cell in vitro. These findings demonstrated that acetylcholine, produced by specialized T-cells that are recruited during C. rodentium infection, are a key mediator in host-microbe interactions and mucosal defenses.

Highlights

The recently revealed degree of integration between the nervous and immune systems are remarkable [1]
We demonstrate that infection with C. rodentium induces choline acetyltransferase (ChAT)+ T-cell recruitment and that expression of ChAT by this T-cell population significantly augments host defenses
To assess if ChAT+ T-cells are recruited during infection, ChAT-GFP+ mice were infected with C. rodentium and the number of CD3+ ChAT-GFP+ T-cells determined by confocal microscopy on days 6, 10, 21, and 30 post-infection (p.i.)

Summary

Introduction

The recently revealed degree of integration between the nervous and immune systems are remarkable [1]. While it is well accepted that neurotransmitters can act on immune cells to alter cell activation and host immune response, recent evidence demonstrates that select immune cell populations respond but can produce neurotransmitters Among these immune cells are the CD4+ T-cells that express choline acetyltransferase (ChAT), the enzyme required for acetylcholine (ACh) biosynthesis [2,3,4]. Neural inhibition of inflammation can inhibit innate immune cell function in preclinical models of inflammatory bowel disease [5], rheumatoid arthritis [6], ischemia reperfusion injury [7, 8], and post-operative ileitis [9] Immune regulation in this pathway requires norepinephrine (NE) released from neurons to activate β2 adrenergic receptors (β2AR) on ChAT+ T-cells causing the release of ACh [2]

Methods

Results

Discussion

Conclusion