Physiological relevance of LL-37 induced bladder inflammation and mast cells

We established the physiological relevance of LL-37 induced bladder inflammation. We hypothesized that 1) human urinary LL-37 is increased in pediatric patients with spina bifida, 2) LL-37 induced inflammation occurs in our mouse model via urothelial binding and is dose dependent and 3) LL-37 induced inflammation involves mast cells.

To test our first hypothesis, we obtained urine samples from 56 pediatric patients with spina bifida and 22 normal patients. LL-37 was measured by enzyme-linked immunosorbent assay. Our second hypothesis was tested in C57Bl/6 mice challenged with 7 LL-37 concentrations intravesically for 1 hour. At 24 hours tissues were examined histologically and myeloperoxidase assay was done to quantitate inflammation. In separate experiments fluorescent LL-37 was instilled and tissues were obtained immediately (time = 0) and at 24 hours (time = 24). To test our final hypothesis, we performed immunohistochemistry for mast cell tryptase and evaluated 5 high power fields per bladder to determine the mean number of mast cells per mm(2).

Urinary LL-37 was 89-fold higher in patients with spina bifida. Mouse LL-37 dose escalation experiments revealed increased inflammation at higher LL-37 concentrations. Fluorescent LL-37 demonstrated global urothelial binding at time = 0 but was not visible at time = 24. Immunohistochemistry for tryptase revealed mast cell infiltration in all tissue layers. At higher concentrations the LL-37 challenge led to significantly greater mast cell infiltration.

Urinary LL-37 was significantly increased in pediatric patients with spina bifida. To our knowledge we report for the first time that LL-37 can elicit profound, dose dependent bladder inflammation involving the urothelium. Finally, inflammation propagation involves mast cells.