Which cells are required for the development of TLR-induced inflammation in the urinary tract? Evidence suggests that both epithelial and non-epithelial cell types may play a role. For instance, when TLR4 mutant C3H/Hej mice were transplanted with wild-type hematopoietic cells, the mice were unable to mount the necessary response to UPEC (30) . By contrast, in a model of cisplatin-induced renal injury, the development of inflammation was dependent on competent TLR4 signaling in resident renal parenchymal cells, as demonstrated in the study of TLR4-/-bone marrow chimeras (31) . Additional work is required to define more accurately the relative roles of TLR signaling within the epithelium versus the leukocytes in the development of mucosal inflammation in the epithelial tract.