Moreover, MZMs have been shown to ingest dying cells and expressed IDO rapidly thereafter; MZM depletion abolished these tolerogenic responses to dying cells, Roxadustat mouse identifying MZMs as key arbiters

of regulatory responses to apoptotic cells [27]. However, the characteristic induction of regulatory cytokines (TGF-β, IL-10) and IDO by apoptotic cells was shown to be abolished in STING-deficient mice and proinflammatory IL-6 expression was induced instead, revealing that cytosolic DNA sensing to activate STING is required for tolerogenic responses to dying cells [33]. Similarly, microbial DNA sensing via STING in splenic or intestinal phagocytes that scavenge blood-borne (such as Streptococcus) or mucosal microbes to prevent sepsis or colitis may reinforce tolerance to protect tissues from immune-mediated damage [39, 40]. Conversely, DNA-induced regulatory responses may promote tumor progression. Tumor-associated inflammation inhibits anti-tumor immunity, and immune cells with regulatory phenotypes such as DCs, macrophages, monocyte-derived suppressor cells, and Treg cells, check details are prominent features of tumor microenvironments; however, the actual molecular pathways that drive regulatory responses to tumor growth are poorly defined. A potential model to explain DNA-induced regulatory responses that drive tumor growth is one

in which DNA from dying tumor cells is sensed via the Immune system STING/IFN-β pathway, which then induces regulatory

ISGs such as IDO, which is expressed in many tumor microenvironments [41]. Interestingly, STING signaling has been shown to induce IFN-αβ-dependent, tumor-specific CD8+ T-cell responses primed by CD8α+ DCs in tumor microenvironments, suggesting that cytosolic DNA sensing may promote effector T-cell responses [42, 43]. Key questions are whether DNA from dying tumor cells is sensed to activate STING and if IFN-αβ released promotes tolerogenic or immunogenic responses during tumor growth, and primes effector T-cell responses following immunotherapy. Similar considerations may be applicable to chronic infections such as leishmaniasis and murine leukemia virus in mice, and HIV-1 in humans, all of which establish localized inflammation that suppresses host immunity and activates host Treg cells [44-46]. DNP treatments have been shown to attenuate limb joint inflammation and cartilage destruction via an IDO-dependent mechanism in a murine model of antigen-induced arthritis [32]. DNP or cdiGMP treatments have also been shown to slow the onset and reduced the severity of MOG-induced EAE [47]. The therapeutic responses were shown to manifest when DNPs were applied either during MOG-immunization or later, when initial EAE symptoms were evident or after disease was fully established [47].