Metabolomic and functional analyses of small molecules secreted by intestinal nematodes in the activation of epithelial tuft cells.

INTRODUCTION: Intestinal helminth parasites trigger the host immune response through epithelial sensory tuft cells, but helminth-derived molecules that may activate tuft cells are poorly characterized. OBJECTIVES: The study aimed to identify small molecules released in vitro by two nematode parasites, that infect rodents (Nippostrongylus brasiliensis) and ruminants (Haemonchus contortus), and to test candidate ligands in an in vivo model of tuft cell differentiation. METHODS: Small molecules were analyzed by hydrophilic interaction liquid chromatography (HILIC) of material released by adult parasites incubated in serum-free media, followed by mass spectrometry; selected molecules were administered to mice and tuft cell expansion enumerated after 5 days. RESULTS: A range of different conditions (culture media, timing, oxygenation) were tested, and comparisons made between the conditions, and between the two nematode species at selected points. Common products across the conditions and species included carboxylic acids (malate, succinate), medium chain fatty acids (such as decanoic and undecanoic acids), purines (guanine, xanthine and their derivatives), and phosphocholine compounds. We selected 19 of the prominent molecules for in vivo testing by oral administration, including succinate, a known activator of tuft cell differentiation. Malate elicited a low but significant level of tuft cell expansion, while undecanoic acids with or without a bromine substitution were also able to induce significant differentiation comparable to succinate. Other molecules including phosphorylcholine had no effect. CONCLUSION: Multiple molecular species including decanoic and undecanoic acids released by helminths may contribute to activation of tuft cells in vivo.