PROJECT ABSTRACT Increased total serum IgE levels are associated with coronary artery disease (CAD). However, the causal role of antigen-specific IgE in CAD remains largely unexplored. Recent work from our group and others provide evidence that humans with IgE sensitization to the mammalian oligosaccharide allergen α-gal have larger coronary artery plaques and unstable plaque features signifying increased CAD compared to those without IgE to α-gal. Yet, whether IgE to α-gal directly promotes atherosclerotic plaque development and the molecular and cellular mechanisms mediating IgE sensitization to α-gal linked to atherosclerosis formation are unknown. Bites from the lone star tick induce IgE sensitization to α-gal and a subsequent severe allergic response when the subject ingests α-gal-containing foods such as red meat. However, the vast majority of individuals with IgE to α-gal do not manifest with delayed anaphylaxis and frequently have no outward identifying symptoms. As such, they continue to consume α-gal-containing food products (meat, dairy, etc.) which have the capacity to continue to stimulate IgE responses and inflammation in the vessel wall. Preliminary data provide the first evidence that humans with IgE sensitization to α-gal had a higher frequency of CCR6+ switched memory (SWM) B cells. Notably, consistent with the association of the IgE sensitization to α-gal and CAD, the amount of CCR6 on SWM B cells was associated with CAD severity. Transcriptomic analysis demonstrated that CCR6+ SWM B cells expressed higher IL-4R and STAT6 in subjects that were IgE α-gal+ compared to IgE α- gal-. Interestingly, IL-4 and STAT6 are important for B cell class switch recombination to IgE, suggesting that cells that make IL-4 may be important in IgE α-gal production. Studying IgE sensitization to α-gal in conventional murine models of atherosclerosis is not feasible as mice, like all lower mammals but unlike humans, express the enzyme galactosyltransferase, produce α-gal and do not develop an IgE response to α- gal. We have obtained a novel α-gal-/- mouse that mimics the human condition to study the role of IgE sensitization to α-gal in atherosclerosis. Comparing α-gal-/- mice to mice wildtype (WT) for α-gal, we show a significant induction of IgE to α-gal after exposure to lone star tick-derived lipids in the α-gal-/- but not the WT mouse. Moreover, preliminary data from mice deficient in NKT cells implicates iNKT cells in the regulation of IgE antibody production to lipids from lone star ticks. Based on these human and murine data, the overarching objective of this proposal is to investigate whether these factors and cells play a causal role in atherosclerosis development due to IgE sensitization to α-gal. We will use loss and gain of function studies in murine atherosclerosis models to define novel mechanisms of α-gal IgE production and the impact of tick-induced α- gal sensitization on diet-induced atherosclerosis, and test a larger cohort of hum...