increasing evidence revealed that another subset of T cells, namely γδ T cells, could even play a dominant role as the source of IL-17 in vivo. We found that γδ T cells in the peritoneal cavity produced IL-17 immediately after Escherichia coli infection, which is critical to the infiltration of neutrophils 10. Furthermore, it was reported that IL-17 production in pulmonary infection see more with BCG was mediated by γδ T cells 11. In the present study, we found BCG treatment in murine bladder also induced IL-17 production by γδ T cells, which play essential role in local neutrophil infiltration and antitumor effect against bladder cancer. Recent studies demonstrated that neutrophils infiltrated in the bladder after BCG treatment played a key role in the antitumor effect 2. In this study, we first examined the kinetics of neutrophil infiltration induced by weekly treatment with BCG. Significant infiltration of neutrophils was observed from one wk after starting BCG treatment, and it gradually increased during the observation period (Fig. 1A). We
then examined Cisplatin in vitro intravesical IL-17 production after single BCG administration. As shown in Fig. 1B, IL-17 production was induced as early as 1 day after BCG injection, but lasted less than 5 days. During the course of repeated BCG administration, similar level of IL-17 production was induced after each injection (Fig. 1C). In order to determine the importance of IL-17 in the infiltration of neutrophils after BCG treatment, we examined the number of intravesical neutrophils in IL-17-deficient mice 22 day after starting BCG treatment. Infiltration of neutrophils was significantly reduced in IL-17-deficient mice (Fig. 2A). Therefore, IL-17 was involved in the infiltration of neutrophils into the bladder after BCG treatment. To examine the significance of IL-17-induced neutrophil infiltration in the antitumor effect of BCG therapy, IL-17 KO mice were inoculated with MB49 bladder cancer cells before BCG treatment
(Fig. 2B). The control B6 mice treated with PIK3C2G BCG exhibited significantly longer survival compared to PBS-treated mice. On the other hand, there was no difference in the survival between BCG- and PBS-treated IL-17-deficient mice. There was also no difference in the survival of PBS-treated B6 and IL-17-deficient mice. We confirmed that depletion of neutrophils completely abrogated the antitumor effect of BCG therapy (data not shown), as was previously demonstrated by others 2. Thus, it was revealed that IL-17-induced neutrophil infiltration was essential for the antitumor effect of intravesical treatment of BCG. In contrast to our results, there have been reports implicating IL-17 with tumor progression. By acting on stromal cells and fibroblasts, IL-17 induces angiogenesis factors, which enhances tumor growth 12, 13.