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

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 IFN, 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-1, IL-6, and TNF, but without significant changes in T-cell and ILC associated IL-17A, IL-22, and IFN, 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 IFN-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. Author summary The nervous system is an active contributor to the regulation of immune responses. Prior studies have identified a unique CD4(+) T-cell population that can relay signals from the sympathetic nervous system. These specialized T-cells express the enzyme choline acetyltransferase (ChAT) and produce acetylcholine (ACh). Release of ACh in response to neurotransmitters from the sympathetic innervation was previously shown to aberrant immune cell activation, reducing mortality during septic shock. Also, these CD4(+) ChAT(+) T-cells were previously found to control host-commensal interactions in naive mice, but their role during enteric bacterial infection was unknown. Here we demonstrate that infection with C. rodentium induces ChAT(+) T-cell recruitment and that expression of ChAT by this T-cell population significantly augments host defenses. These data support a diverse and expanding role of ACh in host immune responses.