PROJECT SUMMARY/ABSTRACT The immune response to Borrelia burgdorferi is complex and at times, enigmatic. Most of the studies that have been done on the immunology of Lyme disease have focused on the role of the lipoproteins that are abundant in the spirochetes. We have shown that B. burgdorferi has unique glycolipids (MGal) and cholesteryl glycolipids (CGal) that have important biological and structural properties and include the ability to induce formation of antibodies. Gamma-delta (γδ) T cells straddle innate and adaptive immunity and are well known for responding to lipid antigens, but responsiveness has only rarely been demonstrated toward a specific bacterial lipid antigen. Based on this information, we tested MGal and CGal for activity to stimulate a specialized γδ T cell capable of long-lived memory formation and co-production of interferon gamma (IFNγ) and IL-17A, cytokines important for anti-pathogen immunity. Surprisingly, MGal was nearly as efficient as live Borrelia in the induction of IFNγ and IL-17A from these nonconventional T cells. These findings led to this proposal whereby we will evaluate the the capacity for MGal and CGal preparations to activate distinct γδ T cell subsets that contribute to anti-pathogen immunity. The function of the γδ T cells will be evaluated using unbiased and large scale cytokine high throughput assays in vitro and in mice, and thereafter, we plan a mechanistic approach to evaluate how these Borrelia lipids elicit γδ T cell functional responses. Given the complexity of the immune response in Lyme disease, this proposal will explore the role of diverse γδ T cell subsets in the response to B. burgdorferi infection. The manner of lipid- elicited γδ T cell function will be determined, and the corresponding functional response of the γδ T cells will be evaluated mechanistically. We anticipate that the γδ T cell-Borrelia axis will be an important contributor to the immune response during Lyme disease.