This demonstrates a STAT4-dependent, IL-12/IL-23-independent pathway of parasite control. Type I IFNs

are important in viral and other infections and can activate STAT4. We found that IFN-α/βR-deficient mice have a nonpersistent, early IFN-γ defect, and a persistent, early IL-10 defect, without changes in serum IL-12 or LN-derived nitric oxide. We found less IL-10 per cell in CD25+CD4+ T cells and possibly fewer IL-10-producing cells in the draining LN of IFN-α/βR-deficient vs. wild-type mice. IFN-α/βR-deficient mice have chronic, nonprogressive disease, like wild-type mice, suggesting that IL-10 and IFN-γ defects may balance each other. Our data indicate that although type I IFNs help promote early Th1 responses, they are not the missing activators of STAT4 responsible for partial control R788 clinical trial of L. mexicana. Also, the lack of lesion resolution in IFN-α/βR-deficient mice despite lower IL-10 levels indicates that other pathways independent of T cell IL-10 help prevent an IL-12-driven clearance of parasites. Leishmania (L.) mexicana, a New World intracellular protozoan parasite, causes chronic cutaneous infection in mice and humans. The immunology and outcome of infection

of L. mexicana are quite different from those of the better-studied Old World relative, L. major. In C57BL/6 (B6) Metformin chemical structure mice, L. major induces a strong Th1 response with interleukin (IL)-12-driven interferon (IFN)-γ from CD4+ T cells. This IFN-γ leads to an upregulation of inducible nitric oxide synthase (iNOS) in infected macrophages, which in turn generates nitric oxide, leading to killing of the intracellular L. major. The outcome is that rapidly growing lesions develop but then heal,

with very low persistent parasite burdens (typically <100 per lesion). In L. mexicana infection of B6 mice, a very weak IFN-γ response occurs and parasites induce chronic, but nonprogressive, lesions that plateau in size at around 10–12 weeks post-infection, with higher parasite burdens (generally 107–108 per lesion). Understanding the similarities and differences between these two related parasite infections is instructive in dissecting the immunological mechanisms. We have found that despite these Florfenicol differing outcomes, many of the pathways involved in control of L. mexicana parallel those seen in L. major infection. B6 mice lacking IFN-γ or iNOS have progressive disease with lesions that do not plateau in size and parasite burdens much higher than in wild-type (WT) mice (1). Interestingly, the Th2 response, as determined by IL-4 production, is not increased in the IFN-γ- and iNOS-deficient mice, showing that susceptibility is because of a lack of an adequate Th1 response rather than an increased Th2 response. We also found that mice lacking STAT4, an important signalling molecule, had progressive disease (1) similar to the increased susceptibility of STAT4 knockout (KO) mice to L. major (2).