Tuft cell-derived acetylcholine promotes epithelial chloride secretion and intestinal helminth clearance.

Epithelial cells secrete chloride to regulate water release at mucosal barriers, supporting both homeostatic hydration and the "weep" response that is critical for type 2 immune defense against parasitic worms (helminths). Epithelial tuft cells in the small intestine sense helminths and release cytokines and lipids to activate type 2 immune cells, but whether they regulate epithelial secretion is unknown. Here, we found that tuft cell activation rapidly induced epithelial chloride secretion in the small intestine. This response required tuft cell sensory functions and tuft cell-derived acetylcholine (ACh), which acted directly on neighboring epithelial cells to stimulate chloride secretion, independent of neurons. Maximal tuft cell-induced chloride secretion coincided with immune restriction of helminths, and clearance was delayed in mice lacking tuft cell-derived ACh, despite normal type 2 inflammation. Thus, we have uncovered an epithelium-intrinsic response unit that uses ACh to couple tuft cell sensing to the secretory defenses of neighboring epithelial cells.

A Tuft Act to Follow: Leukotrienes Take the Stage in Anti-worm Immunity.

Tuft cells are specialized taste-chemosensory cells that detect the presence of intestinal parasites and orchestrate type 2 immunity. In this issue of Immunity, McGinty et al. discover that parasitic worms, but not commensal protists, stimulate tuft cells to release cysteinyl leukotrienes to amplify anti-helminth immunity in the small intestine.

The Taste Receptor TAS1R3 Regulates Small Intestinal Tuft Cell Homeostasis.

Tuft cells are an epithelial cell type critical for initiating type 2 immune responses to parasites and protozoa in the small intestine. To respond to these stimuli, intestinal tuft cells use taste chemosensory signaling pathways, but the role of taste receptors in type 2 immunity is poorly understood. In this study, we show that the taste receptor TAS1R3, which detects sweet and umami in the tongue, also regulates tuft cell responses in the distal small intestine. BALB/c mice, which have an inactive form of TAS1R3, as well as Tas1r3-deficient C57BL6/J mice both have severely impaired responses to tuft cell-inducing signals in the ileum, including the protozoa Tritrichomonas muris and succinate. In contrast, TAS1R3 is not required to mount an immune response to the helminth Heligmosomoides polygyrus, which infects the proximal small intestine. Examination of uninfected Tas1r3-/- mice revealed a modest reduction in the number of tuft cells in the proximal small intestine but a severe decrease in the distal small intestine at homeostasis. Together, these results suggest that TAS1R3 influences intestinal immunity by shaping the epithelial cell landscape at steady-state.

A single-cell survey of the small intestinal epithelium.

Intestinal epithelial cells absorb nutrients, respond to microbes, function as a barrier and help to coordinate immune responses. Here we report profiling of 53,193 individual epithelial cells from the small intestine and organoids of mice, which enabled the identification and characterization of previously unknown subtypes of intestinal epithelial cell and their gene signatures. We found unexpected diversity in hormone-secreting enteroendocrine cells and constructed the taxonomy of newly identified subtypes, and distinguished between two subtypes of tuft cell, one of which expresses the epithelial cytokine Tslp and the pan-immune marker CD45, which was not previously associated with non-haematopoietic cells. We also characterized the ways in which cell-intrinsic states and the proportions of different cell types respond to bacterial and helminth infections: Salmonella infection caused an increase in the abundance of Paneth cells and enterocytes, and broad activation of an antimicrobial program; Heligmosomoides polygyrus caused an increase in the abundance of goblet and tuft cells. Our survey highlights previously unidentified markers and programs, associates sensory molecules with cell types, and uncovers principles of gut homeostasis and response to pathogens.

ChePep controls Helicobacter pylori Infection of the gastric glands and chemotaxis in the Epsilonproteobacteria.

UNLABELLED: Microbes use directed motility to colonize harsh and dynamic environments. We discovered that Helicobacter pylori strains establish bacterial colonies deep in the gastric glands and identified a novel protein, ChePep, necessary to colonize this niche. ChePep is preferentially localized to the flagellar pole. Although mutants lacking ChePep have normal flagellar ultrastructure and are motile, they have a slight defect in swarming ability. By tracking the movement of single bacteria, we found that ΔChePep mutants cannot control the rotation of their flagella and swim with abnormally frequent reversals. These mutants even sustain bursts of movement backwards with the flagella pulling the bacteria. Genetic analysis of the chemotaxis signaling pathway shows that ChePep regulates flagellar rotation through the chemotaxis system. By examining H. pylori within a microscopic pH gradient, we determined that ChePep is critical for regulating chemotactic behavior. The chePep gene is unique to the Epsilonproteobacteria but is found throughout this diverse group. We expressed ChePep from other members of the Epsilonproteobacteria, including the zoonotic pathogen Campylobacter jejuni and the deep sea hydrothermal vent inhabitant Caminibacter mediatlanticus, in H. pylori and found that ChePep is functionally conserved across this class. ChePep represents a new family of chemotaxis regulators unique to the Epsilonproteobacteria and illustrates the different strategies that microbes have evolved to control motility. IMPORTANCE: Helicobacter pylori strains infect half of all humans worldwide and contribute to the development of peptic ulcers and gastric cancer. H. pylori cannot survive within the acidic lumen of the stomach and uses flagella to actively swim to and colonize the protective mucus and epithelium. The chemotaxis system allows H. pylori to navigate by regulating the rotation of its flagella. We identified a new protein, ChePep, which controls chemotaxis in H. pylori. ChePep mutants fail to colonize the gastric glands of mice and are completely outcompeted by normal H. pylori. Genes encoding ChePep are found only in the class Epsilonproteobacteria, which includes the human pathogen Campylobacter jejuni and environmental microbes like the deep-sea hydrothermal vent colonizer Caminibacter mediatlanticus, and we show that ChePep function is conserved in this class. Our study identifies a new colonization factor in H. pylori and also provides insight into the control and evolution of bacterial chemotaxis.