Acute kidney injury (AKI) is a significant factor predisposing chronic kidney disease (CKD), however the factors mediating CKD progression are not clear. T-helper 17 cells (Th17) represent a primary lymphocyte population and may play a central role in coordinating immune and renal cell activity in AKI and subsequent CKD induced by exposure to high salt diet. Studies from the recent project period demonstrated that impairment of IL17 activity attenuates both AKI and progression of CKD and hypertension. We also demonstrated the dependence of Th17 activity on the store-operated calcium channel, Orai1. However, there remains important questions regarding Th17 effects on AKI and CKD. First, the phenotype Th17 cells at different stages of AKI or CKD is not known; second, the physiological regulatory factors modulate Th17 reactivation associated with CKD are not defined; third, the effect of Th17 activity on the variety of potential renal cell targets is incompletely defined. We hypothesize that the dynamic regulation of Th17 cells plays a central role in the development of kidney injury, repair and progression to chronic kidney disease. We propose that Ca2+ signaling stimulated by high-salt diet increases the pathogenicity of Th17 cells by changing their cytokine profile, and further propose that the pleiotropic activity Th17 cytokines such as IL17A and GM-CSF alters parenchymal, innate, and adaptive immune cell function to promote kidney injury. Aim 1 of the proposal will utilize IL17A reporter mice to more completely define the phenotype and localization of Th17 cells using FACS, imaging tissue cytometry and evaluate spatial distribution of Th17 with developing tertiary lymphoid structures (TLS). A Th17 fate- tracing model will be used to characterize whether quiescent Th17 cells following recovery from AKI, express the Orai1- Ca2+ channel, contribute T-memory populations, differentiate to other T-helper populations, or are essential for the reactivation of Th17 cells during progression of CKD. Finally, we will determine if inhibition of these pathways using an FDA approved SOCC blocker following the establishment of AKI during the recovery phase, impairs the secondary activation of Th17 cells associated with progression of CKD. In aim 2, we will expand studies to define alterations in the transcriptional signature of Th17 cells during progressive CKD induced by high salt diet. In addition, we will determine how inhibition of the Th17 pathway by pharmacological and gene knockout approaches affects immune and renal cell transcriptional responses to injury and investigate specific alterations in B-cells and formation of TLS. Finally, we will examine the potential contribution of GM-CSF, a factor co-secreted byTh17 cells, during AK and the AKI to CKD transition.