In addition to its antiprotease and immunomodulatory activities, SLPI has been reported to inhibit the growth of E. coli (47), S. aureus (47), group A Streptococcus (86), and P. aeruginosa (64) in culture, and direct antimicrobial activity against UPEC would certainly explain our observation of increased urine titers in Slpi−/− mice during UTI. Here, SLPI is linked to bacterial urinary tract infection.