Respiratory syncytial virus (RSV) infection isimmunological synapse ͉ virus evasion ͉ virulence mechanism ͉ adaptive immunity R espiratory syncytial virus (RSV) is the worldwide leading cause of infant hospitalization related to airway diseases. RSV infects Ͼ70% of children in the first year of life and by age 2, almost 100% of children have been infected at least once with this virus (1, 2). In addition, RSV reinfection is extremely frequent, suggesting that naturally acquired adaptive immunity to RSV is either inefficient or transient (2-4). It is thought that clearance of RSV would require the induction of a balanced Th1/Th2 adaptive immune response capable of inducing the production of neutralizing antibodies and IFN-␥-secreting cytotoxic CD8 ϩ T cells (CTLs) (5, 6). However, RSV-specific T cell responses generally fail to efficiently clear infection (7-9). Although functional RSV-specific memory CTLs and helper T cells can be observed in the blood and spleens of infected hosts, these cells show impaired effector function in infected lung tissues (10)(11)(12)(13)(14).Dendritic cells (DCs) are ubiquitous professional antigenpresenting cells (APCs) found in lymphoid and nonlymphoid tissues, where they locate strategically to capture antigens and present them to T cells as peptides bound to either MHC class I or II molecules (15, 16). These features render DCs as key components for the initiation and modulation of T cell immunity against pathogens, such as virus. Thus, several virulent microorganisms have developed molecular mechanisms to impair DC function and prevent clearance by adaptive immunity (17-21). RSV infection causes a significant increase in the number of mature DCs in mouse lungs (22,23) and has the capacity to infect and replicate within these cells (24-27), rendering them inefficient at inducing proliferation and IFN-␥ secretion by antigenspecific T cells (24,25). Inhibition of T cell activation by RSV has been suggested to be mediated by soluble molecules secreted by RSV-infected DCs, which reduce their capacity to induce IFN-␥ secretion by T cells (28). Although recent data indicate that RSV-induced secretion of IFN-and -␣ by human DCs can impair T cell activation (29), this phenomenon could also be observed upon T cell culture with RSV particles or cells expressing RSV antigens on their surface (30, 31). However, whether RSV-mediated inhibition applies to cognate pMHC recognition by T cells and the mechanism responsible for this inhibition remain unknown.Here, we have approached these questions by evaluating the effect of RSV infection on the capacity of murine DCs to activate T cells. We observed that DCs are efficiently infected by RSV and, although these cells mature upon infection, they are rendered unable to promote T cell activation in response to cognate-, allo-, and superantigen stimuli. Upon exposure to RSV-infected DCs, T cell proliferation and IL-2 secretion were significantly impaired, and T cells became unresponsive to subsequent stimulation with anti-CD3. Inhibition was not medi...

Emerging evidence has demonstrated that CD4+ T cells infiltrate into the substantia nigra (SN) in Parkinson's disease (PD) patients and in animal models of PD. SN-infiltrated CD4+ T cells bearing inflammatory phenotypes promote microglial activation and strongly contribute to neurodegeneration of dopaminergic neurons. Importantly, altered expression of dopamine receptor D3 (D3R) in PBLs from PD patients has been correlated with disease severity. Moreover, pharmacological evidence has suggested that D3R is involved in IFN-γ production by human CD4+ T cells. In this study, we examined the role of D3R expressed on CD4+ T cells in neurodegeneration of dopaminergic neurons in the SN using a mouse model of PD. Our results show that D3R-deficient mice are strongly protected against loss of dopaminergic neurons and microglial activation during 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD. Notably, D3R-deficient mice become susceptible to MPTP-induced neurodegeneration and microglial activation upon transfer of wild-type (WT) CD4+ T cells. Furthermore, RAG1 knockout mice, which are devoid of T cells and are resistant to MPTP-induced neurodegeneration, become susceptible to MPTP-induced loss of dopaminergic neurons when reconstituted with WT CD4+ T cells but not when transferred with D3R-deficient CD4+ T cells. In agreement, experiments analyzing activation and differentiation of CD4+ T cells revealed that D3R favors both T cell activation and acquisition of the Th1 inflammatory phenotype. These findings indicate that D3R expressed on CD4+ T cells plays a fundamental role in the physiopathology of MPTP-induced PD in a mouse model.

Dendritic cells (DCs) are responsible for priming T cells and for promoting their differentiation from naive T cells into appropriate effector cells. Emerging evidence suggests that neurotransmitters can modulate T cell-mediated immunity. However, the involvement of specific neurotransmitters or receptors remains poorly understood. In this study, we analyzed the role of dopamine in the regulation of DC function. We found that DCs express dopamine receptors as well as the machinery necessary to synthesize, store, and degrade dopamine. Notably, the expression of D5R decreased upon LPS-induced DC maturation. Deficiency of D5R on the surface of DCs impaired LPS-induced IL-23 and IL-12 production and consequently attenuated the activation and proliferation of Ag-specific CD4+ T cells. To determine the relevance of D5R expressed on DCs in vivo, we studied the role of this receptor in the modulation of a CD4+ T cell-driven autoimmunity model. Importantly, D5R-deficient DCs prophylactically transferred into wild-type recipients were able to reduce the severity of experimental autoimmune encephalomyelitis. Furthermore, mice transferred with D5R-deficient DCs displayed a significant reduction in the percentage of Th17 cells infiltrating the CNS without differences in the percentage of Th1 cells compared with animals transferred with wild-type DCs. Our findings demonstrate that by contributing to CD4+ T cell activation and differentiation to Th17 phenotype, D5R expressed on DCs is able to modulate the development of an autoimmune response in vivo.