Type B coxsackievirus (CVB) is a common cause of acute and chronic myocarditis, meningitis and pancreatitis, often leading to heart failure and pancreatic deficiency. dendritic cells up-regulate CD80 and CD86 to a less degree than WT cells. Instead, they up-regulated the inhibitory molecule PD-L1 and secreted considerably PIK-293 lower levels of TNF- PIK-293 and IL-10 and a higher level of IL-23. T lymphocyte proliferation in co-culture with CVB3-infected dendritic cells was increased by TLR3-expressing DCs and other cells. Furthermore, in the absence of TLR3, the T lymphocyte response was shifted toward a Th17 Adamts4 profile, which was previously reported to be deleterious for the host. TLR3-deficient mice were very susceptible to CVB3 infection, with increased pancreatic injury and extensive inflammatory infiltrate in the heart that was associated with uncontrolled viral replication. Adoptive transfer of TLR3+ dendritic cells slightly improved the survival of TLR-deficient mice following CVB3 infection. Therefore, our findings highlight the importance of TLR3 signaling in DCs and in other cells to PIK-293 induce activation and polarization of the CD4+ T lymphocyte response toward a Th1 profile and consequently for a better outcome of CVB3 infection. These data provide new insight into the immune-mediated mechanisms by which CVBs are recognized and cleared in order to prevent the development of myocarditis and pancreatitis and may contribute to the design of therapies for enteroviral infections. Introduction Type B coxsackieviruses (CVBs) are single-stranded (+)-sense RNA viruses that belong to the enterovirus genus and family. They are highly cytolytic and can induce a wide range of acute and chronic diseases, such as myocarditis, meningitis and pancreatitis, with some serotypes being associated with the development of diabetes [1C4]. With a prevalence of 45% amongst infants and adolescents with acute myocarditis or dilated cardiomyopathy, CVB infection is considered one of the most common causes of infectious myocarditis [5C7]. The clinical course of the diseases caused by CVB varies from limited cardiac and pancreatic acinar damage to heart failure and pancreatic deficiency, with increasing patient morbidity and mortality . CVB persistence has been related to chronic cardiomyopathy and pancreatitis , indicating that the virus is able to evade immune surveillance in some circumstances. Accordingly, CVB3 infection causes chronic myocarditis in some mouse strains, such as A.BY/SnJ, A/J and SWR/J , whereas the virus is controlled during the acute phase in other strains, such as 129Sv/J and C57BL/6 [10C12]. In resistant strains, CVB3-induced myocarditis and pancreatitis are abrogated by T lymphocyte-dependent mechanisms, despite the fact that CVB can evade CD8+ T cell responses by reducing its presentation on MHC-I (major histocompatibility complex) . CD4+ T cell priming and polarization as well as the balance of adaptive cytokines are key factors in the outcome of CVB-induced disease. Although the Th1 response contributes to some degree of tissue damage , interferon (IFN)–producing Th1 cells are responsible for controlling CVB and resolving the infection . In contrast, a Th17-skewed immune response is harmful to the host, as it is unable to control viral replication and contributes to tissue damage, worsening the CVB infection scenario [16,17]. Th2 cytokines are associated with both improvement [18,19] and aggravation  of CVB-induced disease. The intensity of the response and the microenvironment in which these cytokines are produced might influence the balance of the immune response and the outcome of infection. Indeed, a Th1 response together with the PIK-293 presence of regulatory T cells in target tissues is crucial in providing the regulation necessary for preventing tissue injury [21C23]. The priming and polarization of T lymphocyte responses depend on viral recognition by antigen-presenting cells. Viral RNA is sensed by toll-like receptors (TLRs) and RIG-I-like receptors (RLRs). RIG-I and MDA-5 are cytosolic helicases that detect distinct forms of dsRNA that accumulate in the cytosol upon viral replication. Their expression is induced by type I interferon (IFN-I) in most cell types . Among the TLRs, TLR3 and TLR7/8 recognize dsRNA and ssRNA, respectively. Viral RNA becomes accessible to these receptors in the endosome either upon phagocytosis of infected apoptotic cells, the internalization of immune complexes with viral RNA, or by autophagy of cytoplasmic RNA. Although some stromal cells express RNA-recognizing TLRs, these receptors are mainly expressed by antigen-presenting cells, especially dendritic cells (DCs) and macrophages [25,26]. TLRs activate overlapping but different signaling pathways upon stimulation. The intracellular adaptor protein MyD88, which is activated by all TLRs except TLR3, worsens CVB3-induced cardiac injury . In contrast, TLR3- and TLR4-dependent TRIF signaling is essential for the antiviral response and has been implicated in the improvement of the disease [28,29]. TLR3-TRIF signaling results in the phosphorylation and nuclear translocation of the transcription factors IRF3 and NF-B, which are crucial for the production of type I IFN and proinflammatory cytokines, respectively [30,31]. Innate immunity against CVB is.