Contribution of mast cells to bacterial clearance and their proliferation during experimental cystitis induced by type 1 fimbriated E. coli

Bacterial infections of the urinary bladder are very common, and the role of mast cells in these infections is invariably thought of as a detrimental one. However, recent studies have shown that mast cells play a key role in host defense against various enterobacterial infections. In this manuscript, using mast cell-deficient (WBB6F₁-W/W^v) and mast cell-sufficient (WBB6F₁-+/+) mice we have investigated the protective role of mast cells in urinary bladder infections in vivo. Our findings show that (i) the mast cells are activated by FimH-expressing E. coli, and release large amount of histamine in the urinary bladder; (ii) the number of surviving bacteria in the urine is dependent on the presence of mast cells, and (iii) mast cell number in the bladder increases following uropathogenic infection in mice which is likely due to an increase in the mast cell growth-promoting cytokine IL-3 in bacteria-activated mast cells. Taken together, these observations suggest a beneficial role of mast cells in urinary bladder infections in mice.