Project Summary Allergies affect millions of Americans and are exacerbated by bacterial infection. Despite mainstay therapies that suppress immune responses to allergy or bacteria, these health issues continue to persist. An unexplored target for new therapies lies with neural surveillance and regulation of immunity. However, this neural influence is poorly understood and seemingly paradoxical: immune responses are exacerbated in allergy, but in response to bacterial infection, the neural response reduces inflammation. How might this happen? One possibility is that the peripheral neural-immune sensing apparatus might be altered by such factors as immunoglobulin profiles, and gender, implying the participation of sex hormones. We hypothesize that such variables affect the transcriptome and thereby the excitability of the vagus and carotid bodies. Studies in AIM 1 will use single-cell RNAseq analysis of vagal and carotid body ganglia from male and female mice with asthma, pneumonia to identify how these nerves are changed in response to each condition. Then, we will assess nerve activity in response to immunoglobulin stimuli of each ganglia using state-of-the-art electrophysiological recording techniques. This project will reveal which neural cluster (vagus vs. carotid body) is the predominant sensory ganglia involved in regulating allergic vs. bacterial immune responses and how sex may affect neuro- immune signalling. Studies in AIM 2 will utilize DTR (diphtheria toxin receptor) technology in mice to selectively ablate cells where DTR expression is driven by TRPV1 (transient receptor potential vanilloid 1) or TH (tyrosine hydroxylase). Use of these transgenic mice will allow ablation of either vagal (TRPV1-DTR) or carotid body (TH- DTR) centers by direct neural microinjection of diphtheria toxin (DTX) into vagal or carotid body ganglia using saline injections as control. We will then expose mice to either allergen or bacterial infections. DTX injections will selectively abolish neuronal function and reveal which ganglion is the predominant neuro-immune sensor in the specified condition in male and female mice. These data will: 1) identify how the response to allergic or bacterial stimuli alters receptor gene expression in order to identify the phenotypic switch from anti- to pro-inflammatory neural-immune signalling; 2) establish a model and sex differences that will set the stage for further investigation involving targeted knockdown within neuro-immune sensing ganglia to discern function; 3) validate our models and methods for future investigations into the role of neural-immune sensing in disease states.