Pyelonephritis continues to result in considerable morbidity, mortality and health care expense. To develop new treatment strategies, a more thorough understanding of the kidney’s role in the innate defense of the kidney and urinary tract is needed. Our research has identified a murine intercalated cell deficiency model that is susceptible to pyelonephritis. We have also demonstrated that human and murine intercalated cells produce and secrete antimicrobial peptides. Others have demonstrated that intercalated cells act as the first site in the kidney that responds to Gram-negative organisms via pattern recognition receptor signaling pathways. Thus, surmounting evidence suggests that intercalated cells perform a critical role in the innate defense of the kidney. In prior studies we performed single cell mRNA sequencing on human kidneys following stimulation with uropathogenic E. coli. “Phagosome maturation” was a key intercalated cell pathway. We then developed methodology to visualize bacteria phagocytosing bacteria and demonstrated this function in real-time. We hypothesize that intercalated cells employ the processes to phagocytose bacteria that they utilize to regulate acid-base balance and that this phagocytosis may be enhanced during UTI. We know that intercalated cells can phagocytose bacteria. We will explore the role of carbonic anhydrase and V-ATPase in intercalated cell phagocytosis using real time imaging in live mice (Aim 1a), complementary flow cytometry studies (Aim 1b) and on pyelonephritis susceptibility (Aim 1c) Our long-term research goal is to develop new pyelonephritis treatment strategies that reduce antibiotic exposure and preserve renal function in populations at risk. The proposed research will provide the foundation to include modulation of intercalated cells in pyelonephritis management, thereby expanding treatment scope beyond antibiotics.