Enteric neuro-immune interactions in host defense

Abstract

The enteric nervous system (ENS) can profoundly influence gut immune cell function and the inflammatory response. However, despite the numerous examples of ENS-derived neuropeptides modulating immune cell function, our understanding of how enteric neurons directly sense inflammatory cues produced during infection is considerably lacking. Therefore, a thorough characterization of the mediators capable of being sensed by enteric neurons is critical to understanding enteric neuron function and dysfunction in gastrointestinal disease. To survey the expression of immune-related receptors on enteric neurons, we integrated three publicly available single-cell RNA-sequencing (scRNA-seq) datasets profiling enteric neurons of the small intestine, finding that the single cluster of primary enteric sensory neurons (PSNs) co-expressing Nmu and Calcb, encoding the immunomodulatory neuropeptides NMU and CGRPβ, was highly enriched in genes encoding the receptor for the type 2 cytokines IL-4 and IL-13 and its essential signaling components. Using in vitro enteric neuro-glial cultures and in vivo mouse models of PSN-specific Il13ra1 deletion, we discovered that direct PSN recognition of IL-4 and IL-13 is sufficient to upregulate NMU and CGRPβ expression. Furthermore, deletion of Il13ra1 in PSNs impaired host defense to the gastrointestinal helminth H. polygyrus and significantly diminished duodenal PSN neuropeptide expression, PSN innervation to the villi, and PSN abundance in the myenteric plexus. Moreover, PSN Il13ra1 deletion blunted anti-helminth type 2 immune responses in a site-specific manner, reducing Il5 expression in muscularis ILC2s, eosinophil recruitment to the muscularis, and muscularis macrophage (MMφ) expression of genes involved in tissue repair and anti-helminthic immunity, like Arg1/arginase-1. Importantly, co-administration of NMU23 and CGRPβ rescued helminth clearance deficits and restored type 2 immunity and MMφ arginase-1 expression. In summary, our work illustrates the importance of direct cytokine sensing by PSNs during gastrointestinal helminth infection and delineates a mechanism of site-specific anti-helminth immunity in the muscularis externa. We further define how the highly correlated NMU and CGRPβ expression in PSNs promotes appropriate muscularis-specific anti-helminth immunity while buffering inflammatory tissue-damage, highlighting the essential bi-directional neuro-immune crosstalk regulating intestinal type 2 inflammation.