Hostile bile limits anti-cancer immunity.

Various microbial metabolites promote cell transformation. In this issue of Immunity, Cong et al. show that deoxycholic acid (DCA), a microbial metabolite of bile, promotes tumor growth by suppressing antitumor CD8+ T cell responses via dysregulation of calcium efflux.

TCF-1 limits intraepithelial lymphocyte antitumor immunity in colorectal carcinoma.

Intraepithelial lymphocytes (IELs), including αß and γδ T cells (T-IELs), constantly survey and play a critical role in maintaining the gastrointestinal epithelium. We show that cytotoxic molecules important for defense against cancer were highly expressed by T-IELs in the small intestine. In contrast, abundance of colonic T-IELs was dependent on the microbiome and displayed higher expression of TCF-1/TCF7 and a reduced effector and cytotoxic profile, including low expression of granzymes. Targeted deletion of TCF-1 in γδ T-IELs induced a distinct effector profile and reduced colon tumor formation in mice. In addition, TCF-1 expression was significantly reduced in γδ T-IELs present in human colorectal cancers (CRCs) compared with normal healthy colon, which strongly correlated with an enhanced γδ T-IEL effector phenotype and improved patient survival. Our work identifies TCF-1 as a colon-specific T-IEL transcriptional regulator that could inform new immunotherapy strategies to treat CRC.

Neonatal antibiotics have long term sex-dependent effects on the enteric nervous system.

Infants and young children receive the highest exposures to antibiotics globally. Although there is building evidence that early life exposure to antibiotics increases susceptibility to various diseases including gut disorders later in life, the lasting impact of early life antibiotics on the physiology of the gut and its enteric nervous system (ENS) remains unclear. We treated neonatal mice with the antibiotic vancomycin during their first 10 postnatal days, then examined potential lasting effects of the antibiotic treatment on their colons during young adulthood (6 weeks old). We found that neonatal vancomycin treatment disrupted the gut functions of young adult female and male mice differently. Antibiotic-exposed females had significantly longer whole gut transit while antibiotic-treated males had significantly lower faecal weights compared to controls. Both male and female antibiotic-treated mice had greater percentages of faecal water content. Neonatal vancomycin treatment also had sexually dimorphic impacts on the neurochemistry and Ca2+ activity of young adult myenteric and submucosal neurons. Myenteric neurons of male mice were more disrupted than those of females, while opposing changes in submucosal neurons were seen in each sex. Neonatal vancomycin also induced sustained changes in colonic microbiota and lasting depletion of mucosal serotonin (5-HT) levels. Antibiotic impacts on microbiota and mucosal 5-HT were not sex-dependent, but we propose that the responses of the host to these changes are sex-specific. This first demonstration of long-term impacts of neonatal antibiotics on the ENS, gut microbiota and mucosal 5-HT has important implications for gut function and other physiological systems of the host. KEY POINTS: Early life exposure to antibiotics can increase susceptibility to diseases including functional gastrointestinal (GI) disorders later in life. Yet, the lasting impact of this common therapy on the gut and its enteric nervous system (ENS) remains unclear. We investigated the long-term impact of neonatal antibiotic treatment by treating mice with the antibiotic vancomycin during their neonatal period, then examining their colons during young adulthood. Adolescent female mice given neonatal vancomycin treatment had significantly longer whole gut transit times, while adolescent male and female mice treated with neonatal antibiotics had significantly wetter stools. Effects of neonatal vancomycin treatment on the neurochemistry and Ca2+ activity of myenteric and submucosal neurons were sexually dimorphic. Neonatal vancomycin also had lasting effects on the colonic microbiome and mucosal serotonin biosynthesis that were not sex-dependent. Different male and female responses to antibiotic-induced disruptions of the ENS, microbiota and mucosal serotonin biosynthesis can lead to sex-specific impacts on gut function.

Antibiotic exposure postweaning disrupts the neurochemistry and function of enteric neurons mediating colonic motor activity.

The period during and immediately after weaning is an important developmental window when marked shifts in gut microbiota can regulate the maturation of the enteric nervous system (ENS). Because microbiota-derived signals that modulate ENS development are poorly understood, we examined the physiological impact of the broad spectrum of antibiotic, vancomycin-administered postweaning on colonic motility, neurochemistry of enteric neurons, and neuronal excitability. The functional impact of vancomycin on enteric neurons was investigated by Ca2+ imaging in Wnt1-Cre;R26R-GCaMP3 reporter mice to characterize alterations in the submucosal and the myenteric plexus, which contains the neuronal circuitry controlling gut motility. 16S rDNA sequencing of fecal specimens after oral vancomycin demonstrated significant deviations in microbiota abundance, diversity, and community composition. Vancomycin significantly increased the relative family rank abundance of Akkermansiaceae, Lactobacillaceae, and Enterobacteriaceae at the expense of Lachnospiraceae and Bacteroidaceae. In sharp contrast to neonatal vancomycin exposure, microbiota compositional shifts in weaned animals were associated with slower colonic migrating motor complexes (CMMCs) without mucosal serotonin biosynthesis being altered. The slowing of CMMCs is linked to disruptions in the neurochemistry of the underlying enteric circuitry. This included significant reductions in cholinergic and calbindin+ myenteric neurons, neuronal nitric oxide synthase+ submucosal neurons, neurofilament M+ enteric neurons, and increased proportions of cholinergic submucosal neurons. The antibiotic treatment also increased transmission and responsiveness in myenteric and submucosal neurons that may enhance inhibitory motor pathways, leading to slower CMMCs. Differential vancomycin responses during neonatal and weaning periods in mice highlight the developmental-specific impact of antibiotics on colonic enteric circuitry and motility.

The enteric nervous system undergoes significant chemical and synaptic maturation during adolescence in mice.

Adolescence is a critical period of development. It is very likely that there is significant maturation of the enteric nervous system (ENS) of the gut during this stage of life, especially since there are substantial changes in factors known to influence the ENS including diet and microbiota during this time, but this remains unknown. To examine maturation of the ENS during adolescence, we performed immunohistochemistry using advanced microscopy and analytical methods to compare enteric neurons and glia of the duodenum and colon of mice taken prior to weaning with those of young adult mice. We found significant changes in the architecture of both myenteric and submucosal plexuses and surprisingly found subsets of enteric cells that co-expressed the pan-neuronal marker, Hu, and either glial markers Sox10 or S100ß, not both. About 70% and 35% of all Hu â€‹+ â€‹neurons in the submucous plexus of the young adult duodenum and colon respectively also expressed S100ß. The proportion of Hu+/Sox10 â€‹+ â€‹cells in the duodenal myenteric plexus decreased, while the proportion of Hu+/S100ß+ cells in the colonic submucosal plexus increased during adolescence. In the submucous plexus, there were significant increases in the proportions of vasoactive intestinal peptide+ and choline acetyltransferase â€‹+ â€‹secretomotor neurons, of neurofilament M (NFM)+ neurons in the colon and of calretinin â€‹+ â€‹neurons in the duodenum during adolescence. There were no age-dependent changes in the neurochemistry of various myenteric neuronal subtypes, including those immunoreactive for neuronal nitric oxide synthase (nNOS), Calbindin, Calretinin or NFM. There were significant increases in the somata sizes of Calretinin â€‹+ â€‹submucosal and myenteric neurons, and nNOS â€‹+ â€‹myenteric neurons, and these enteric neurons received significantly more synaptophysin â€‹+ â€‹contacts onto their cell bodies during adolescence. This is the first study showing that enteric neurons and glia in the gut undergo significant changes in their anatomy and chemistry during adolescence. Notably changes in synaptic contacts within the enteric circuitry strongly suggest maturation in gastrointestinal function occurs during this time.