Project Summary The skin functions as a protective physical barrier as well as an immunologic organ that protects the host from pathogens but is also subject to autoinflammatory disease. Immunity in the skin involves the development of inflammatory cytokine cascades between different cell types that both promote host defense but are pathogenic in disease. For example, IL-23 from dermal dendritic cells drives production of IL-17 from T cells resulting inn host defense against extracellular pathogens but this cascade is also pathogenic in diseases such as psoriasis vulgaris and hidradenitis suppurative. A similar cascade involving IL-4 and IL-13 has been described for defense against parasites and atopic dermatitis. Recently, it has become appreciated that TRPV1-expressing cutaneous neurons play an obligate role in cutaneous inflammation across a wide variety of contexts, but the exact mechanism remains unknown. In the past cycle of this grant we explored whether activation of TRPV1-expressing neurons in the absence of any tissue damage could trigger inflammation. Using optogenetics, we found that multiple rounds of activation of TRPV1-expressing neurons with laser light was sufficient to trigger Type-17 inflammation which was dependent on the neuropeptide CGRP released from sensory nerve terminals and dermal dendritic cells. Host defense against epicutaneous C. albicans and S. aureus infection was augmented, and both the Type-17 inflammation and host defense extended beyond the site of stimulation through a nerve reflex arc providing regional anticipatory immunity. The temporal precision of optogenetic stimulation allows us to interrogate the early stages of TRPV1- mediated neuroinflammation. In this proposal we seek to test the hypothesis that neuroinflammation triggered by TRPV1-expressing neurons initially activates mast cells resulting in clustering of immune cells which then allows for CGRP-dependent production of IL-23 from dermal dendritic cells. We will also test whether TRPV1-expressing neurons not only trigger inflammation but also provide a positive feed-back loop that is required to maintain ongoing inflammation. Finally, we examine whether stimulation of TRPV1-expressing neurons affect adaptive immunity and is sufficient to trigger Th17 differentiation and reactivation of cutaneous resident memory Th17. Our expectation is that by more fully delineating neuroinflammatory pathways, we will obtain basic insight into the development of innate immune responses and allow for potential therapeutic intervention. Moreover, modulation of adaptive immunity by TRPV1-expressing neurons would link neuroinflammation with flares in established Type-17 autoimmune diseases such as psoriasis as well as potentially with the development of autoimmunity associated with chronic pain