PROJECT SUMMARY Helminth parasites, including hookworms, infect approximately 2 billion people worldwide and represent a significant public health concern. To combat these parasites, the mammalian immune system has evolved mechanisms to maintain a delicate balance between promoting beneficial inflammation needed to reduce parasitic burdens, but also subsequently restricting that inflammation once the infectious threat is eliminated. When properly regulated, this allows for protective immunity to be achieved without the development of unwanted immunopathology. It is well established that type 2 inflammation, characteristic of helminth-induced immune responses in humans and mice, is initiated via the production of type 2 cytokines by group 2 innate lymphoid cells (ILC2s) and type 2 T helper (TH2) cells. The activation of both innate and adaptive lymphocytes results in the induction of smooth muscle contraction, eosinophilia, mucus production and the population expansion of basophils. Despite our knowledge of the factors that promote type 2 inflammation, the mechanisms that restrict its ability to promote immunopathology remain poorly defined. Our preliminary studies revealed that helminth-induced ILC2 responses, type 2 cytokine production, lung eosinophilia and mucus production are significantly elevated following the depletion of basophils. Moreover, depletion of basophils resulted in dramatic lung pathology and decreased lung function. Strikingly, our new studies also revealed that ILC2s activated in the absence of basophils failed to upregulate expression of the receptor for the neuropeptide neuromedin b (Nmb). Further, delivery of Nmb to helminth-infected mice resulted in reduced ILC2 responses, eosinophilia and mucus production. These data suggest that Nmb is a potent inhibitor of type 2 inflammation. Nmb belongs to the bombesin-like family of neuropeptides consisting of neuromedin B, N, S and U. Importantly, neuromedin U was recently shown to be an important positive regulator of helminth- induced ILC2 responses. Collectively, our studies suggesting that Nmu and Nmb operate as neuropeptide ‘rheostat’ that properly balances helminth-induced inflammation. Based on our strong preliminary studies and generation of novel Nmbr-floxed and Nmur-Cre mouse models, three specific aims will address the following questions: (i) Do helminth-induced basophils regulate Neuromedin b receptor expression on immune cells, (ii) Does Nmb restrict the activation of multiple immune cells in a manner that properly regulates helminth-induced inflammation, and (iii) Do Nmu and Nmb directly counterbalance each other and operate as a neuropeptide rheostat? Collectively, these studies will interrogate novel mechanisms through which type 2 cytokine- mediated immunity and inflammation are negatively regulated. Defining the mechanisms through which basophils initiate a Nmu/Nmb-mediated rheostat may inform new therapeutic strategies to treat helminth- induced immunopathology.