Innate immune responses to bladder infection
The urinary tract (UT) consists of the kidneys, ureters, bladder, and urethra, all of which with the exception of the lower urethra are presumed to be sterile. Because of its close proximity to the gut, the lower UT is constantly exposed to a barrage of gut bacteria. However, the bladder remains for the most part free of infection. The resistance of the bladder to active microbial colonization is due to both anatomical design as well as secreted antimicrobial compounds of the urothelium. The apical face of the urothelium is covered by uroplakin plaques and is coated by mucus, which discourages adherence and invasion of most microorganisms (1, 2). Because of its role in storing urine for extended periods of time, the urothelium of the bladder has an additional role in protecting the underlying tissue from urine and its many toxic constituents. Since the bladder and urinary system as a whole need to constantly maintain the integrity of the urothelium, immune responses in the UT are often tightly regulated to minimize the extent of damage by quelling inflammation in a timely manner.