The innate response to uropathogens: the urothelial defendome.

Urinary tract infections (UTIs) will affect half of the female population within their lifetime. The urothelium, the epithelial lining which lines the urinary tract, plays an important role in mediating the defense against UTIs. Recent work has suggested that significant differences exist between normal human urothelial cell responses to uropathogenic stimuli and the responses observed in murine and cancer cell models. The work described in this thesis aimed to investigate the urothelial defendome: the soluble component of urothelial innate immunity, with a specific focus on antimicrobial peptides (AMPs), using in vitro models of uropathogenic E. coli (UPEC) interaction with normal human urothelial (NHU) cells.
NHU cells expressed several antimicrobial peptide (AMP) genes constitutively and in response to UPEC. Beta-defensin 2 and 4 were upregulated in response to UPEC and isolated UPEC flagellin, but not in response to other isolated virulence factors. Despite expressing the flagellin receptor Toll-like receptor 5, barrier-presenting differentiated NHU cells did not exhibit an AMP response to UPEC or UPEC-derived flagellin. Damaging the urothelial barrier before flagellin exposure induced AMP expression, a response previously not shown in vivo or in vitro. Immunolocalisation studies revealed TLR5 to be expressed sub-apically, suggesting a possible novel mechanism of immunomodulation by the urothelium.
These results strongly support the concept of human urothelium as the crux of innate immune functionality in the urinary tract. The damage-dependent response exhibited by biomimetically differentiated NHU cells to uropathogenic stimuli suggests that the state of the urothelial barrier may play an important role in controlling urothelial immunity.