A growing body of evidence indicates that the kidneys contribute substantially to immune defense against pathogens in the urinary tract. In this issue, Paragas et al. report that α-intercalated cells (A-ICs) within the nephron collecting duct sense infecting Gram-negative bacteria, resulting in simultaneously secretion of the iron chelating protein lipocalin 2 (LCN2) and protons, which acidify the urine. A-IC-specific LCN2 and proton secretion markedly reduced the ability of infecting uropathogenicE. coli(UPEC) to grow and sustain infection. The capacity of A-ICs to sense and actively promote clearance of infecting bacteria in the lower urinary tract represents a novel function for these specialized kidney cells, which are best known for their role in modulating acid-base homeostasis.