Project Summary/Abstract The cutaneous sensory nervous system plays an essential role in the recognition of allergens and activation of the allergic immune response. Protease allergens directly activate pruriceptive, or itch-inducing, sensory neurons, leading to the sensation of itch and the local release of Substance P, which then activates and promotes the migration of allergic-skewing dendritic cells into the draining lymph node. Our laboratory is focused on understanding these neuro-immune interactions, specifically in identifying how pruriceptive sensory neurons detect allergens, what subsets of pruriceptive neurons are involved in this detection, and how sensory neuron-dendritic cell interactions are maintained in the skin. In order to better understand the neuro-immune mechanisms controlling the initiation of the allergic immune response, we propose to study how aging leads to defects in these mechanisms. Despite our continued exposure to new and novel allergens, the development of new allergic sensitizations is inversely correlated with age. At the same time, the itch response in the elderly is dysfunctional, with chronic pressure-induced itch being one of the most frequent symptoms in individuals over 65 years of age. If allergen-induced activation of pruriceptive neurons is directly upstream of allergic sensitization, what explains the low incidence of novel allergic sensitization in the very population with the highest prevalence of itch? Our central hypothesis is that aging leads to altered neuro-immune interactions within the dorsal root ganglia (the anatomical location of sensory neuron cell bodies) and the skin, resulting in dysfunctional itch responses and defective neuronal responses to allergens. Building upon our laboratory’s expertise in innate immunology, allergy and neuro-immunology, and taking the novel approach of comparing allergen sensitive young adult mice with allergen insensitive aged mice, we will use the tools of single cell and single nuclear transcriptomics, cellular immunology, and neurobiology to gain a fundamental understanding of the neuro-immune interactions required to initiate and maintain allergic immunity. We will test our central hypothesis in two specific aims: (1) identify the age-related changes that alter the sensory neuronal response to allergens, and (2) determine the role of age-related changes in sensory neuron function in the initiation of allergic immune responses. Aim 1 will examine how immune cell infiltration into aged dorsal root ganglia alters sensory neuronal populations and the sensitivity of those neurons to allergen-induced activation in both mice and humans. Aim 2 will focus on the skin, the site of allergen exposure, and address how aging alters the interactions between pruriceptive neurons and dendritic cells, and how age-induced alterations then impact the initiation of the allergic immune response. By studying the physiologic processes that control itch and allergic immune initiat...