´╗┐Interleukin-17 receptor deficiency results in impaired synovial expression of interleukin-1 and matrix metalloproteinases 3, 9, and 13 and prevents cartilage destruction during chronic reactivated streptococcal cell wall-induced arthritis

´╗┐Interleukin-17 receptor deficiency results in impaired synovial expression of interleukin-1 and matrix metalloproteinases 3, 9, and 13 and prevents cartilage destruction during chronic reactivated streptococcal cell wall-induced arthritis. mice. These data demonstrate that IL-17 mediated responses promote tumor development through the induction of tumor promoting microenvironments at tumor sites. IL-17 mediated regulation of MDSC is a primary mechanism for its tumor promoting effects. The study provides novel insights into the role of IL-17 in tumor development and has major implications for targeting IL-17 in treatment of tumors. strong class=”kwd-title” Keywords: IL-17, tumor, myeloid derived suppressor cells, CD8 T cells, IFN- INTRODUCTION Immune responses have paradoxical roles in tumor development (1, 2). On one side, immune responses play a key role in immune-surveillance for prevention of tumor development. Numerous studies indicate that anti-tumor immune responses are able to prevent and eliminate tumors. On the other side, however, immune responses, especially in a form of chronic inflammation, promote tumor development in many cases (3, 4). A prominent feature of tumor promoting immune responses is the increased number of myeloid derived suppressor cells (MDSC) in the blood, spleen and bone marrow and abundant infiltration of Mmp17 MDSC at the tumor site (5C8). Heavy infiltration of MDSC has been considered as a major cause for immunosuppression at tumor sites (5, 8, 9). MDSC are considered as an immature form of myeloid cells which are mostly identified as CD11b and Gr-1 double positive cells in mice (7, 10). MDSC are able to suppress anti-tumor immune responses and promote tumor growth (5, 8). Recent studies have shown that MDSC are composed of two subpopulations, which suppress T cell responses by different mechanisms (11, 12). Inflammatory cytokines and tumor derived mediators have been reported to regulate MDSC (5C8). However, mechanisms for the development and function of MDSC remain to be fully elucidated. IL-17 is an inflammatory cytokine secreted by CD4 Th17 and CD8 Tc17 cells (13C17). Six IL-17 family members (IL-17A-F) have been described and the prototype member of the family is IL-17A, often termed IL-17 in literature. The receptor for IL-17A and IL-17F is IL-17RA, generally termed IL-17R Guanosine 5′-diphosphate disodium salt which is expressed ubiquitously (14). IL-17 plays an important role in the regulation of leukocyte migration in inflammatory reactions and a defect in IL-17R decreases the expression of cytokines, chemokines and reduces the infiltration of inflammatory cells, especially neutrophils (18C23). The role of IL-17 in inflammatory and autoimmune diseases has been extensively studied (13, 15, 16, 24). Although IL-17 producing cells are detected in cancer patients and tumor bearing mice (25C28), the role of IL-17 in tumor development is controversial (22, 29C35). Recent reports indicate that tumor growth is Guanosine 5′-diphosphate disodium salt increased in IL-17?/? mice and that the mechanism is associated with IFN- producing NK and T cells (32, 35). It implicates that IL-17 mediated responses are protective against tumor development. However, another recent report shows that tumor growth is suppressed in IL-17?/? and IL-17/IFN- double knockout mice (31). A mechanism is that Guanosine 5′-diphosphate disodium salt IL-17 induces the production of IL-6 by tumor cells, which in turn promotes tumor growth in a Stat-3 dependent pathway. Interestingly, the report shows that the production of IFN- by tumor infiltrating T cells from IL-17?/? mice is increased (31). Although IFN- plays a role in the regulation of anti-tumor immune responses (36C38), CTL activity of tumor specific T cells is an important mechanism for T cell mediated tumor rejection. It is not examined whether IL-17 regulates the CTL activity of tumor specific CD8 T cells. Moreover, it is largely unknown whether IL-17 mediated effects on innate immune cells, such as MDSC, play a role in tumor immune responses. It is often observed that T cells from tumor patients retain the ability to respond to tumor antigens. However, immune responses in peripherals are not correlated with tumor rejection (39C41). Mechanisms for immunosuppression include failure of immune T cell infiltration into tumors and presence of Treg cells and immune suppressive myeloid cells at tumor sites (8, 42C44). The infiltration of immune T cells in tumors is associated with good prognosis (45) whereas infiltration of MDSC is associated with poor prognosis.