Understanding the Role of Tick Phospholipase A2 in Alpha-Gal Syndrome - Project Summary Alpha Gal Syndrome (AGS) is an allergy to red meat, which is induced by the bite of the lone star ticks (Amblyomma americanum). The unexpected increase in tick-borne diseases, including AGS, is a significant threat to human health without reliable diagnostic tools and preventive measures. Food allergies negatively affect ~32 million Americans, and the number of confirmed AGS cases has risen from 12 in 2009 to >450,000 in 2022 in the United States alone. Unfortunately, there is no cure for AGS or other food allergies. Given the strong evidence of Am. americanum bites give rise to a strong IgE response; the key question is how tick bites drive the human immune system towards developing a T-helper 2 (Th2) response leading to AGS development? Notably, the α-gal antigen is abundant in both Am. americanum, and Ixodes scapularis saliva, but only Am. americanum is associated with AGS, additional factors must be involved. Am. americanum saliva contains high titers of soluble phospholipase A2 (Aa_sPLA2) an enzyme that hydrolyses phospholipids such as phosphatidylcholine and phosphoethanolomine, generating arachidonic acid (AA). The salivary Aa_sPLA2 has been implicated in the refractoriness of A. americanum to Borrelia burgdorferi transmission. The lack of toxicity of I. scapularis saliva to B. burgdorferi, on the other hand, suggests that sPLA2 activity is low or absent in this species. AA generated by Aa_sPLA2 might contribute to AGS in multiple ways. In particular, AA is the substrate used to generate eicosanoids including cysteinyl leukotrienes (CysLTs) LTB4 and LTC4, and the prostaglandin PGD2 by immune cells including mast cells in the skin, with consequent immunomodulatory effects. CysLTs induce the production of the Th2 cytokines IL-4, IL-5, and IL-13 by ILC2-type lymphoid cells, and expansion of Th2 cells and eosinophils after allergen challenge. Altogether these observations lead us to the central hypothesis that it is the Aa_sPLA2 that interacts with the α-gal allergen in A. americanum saliva to generate AGS. In this study, we propose to use an α-gal-KO mouse model that mimics the human lack of α-gal to study the role of tick saliva secretory Phospholipase A2 in AGS development. In Aim 1, an RNA interference approach will deplete the Aa-sPLA2 in female adult ticks to assess the role in AGS development in an α-gal-KO mouse model. In Aim 2, we will use Aa_sPLAs silenced nymphs to sensitize the α-gal-KO mice to study the host immune responses, including the role of Cys-leukotrienes and prostaglandins, associated with AGS development. The results of these experiments will provide insight into how Am. americanum bites skew the immune response from TH1 toward TH2 immunity leading to AGS development and the production of α- gal sIgE. In addition, these experiments are expected to provide basic knowledge related to the role of tick saliva antigens in inducing AGS, which will subsequently direct targeted therapies.
