[Abstract unavailable

Increasing evidence suggests that Alzheimer's disease pathogenesis is not restricted to the neuronal compartment but strongly interacts with immunological mechanisms in the brain. Misfolded and aggregated proteins bind to pattern recognition receptors on micro- and astroglia and trigger an innate immune response, characterized by the release of inflammatory mediators, which contribute to disease progression and severity. Genome wide analysis suggests that several genes, which increase the risk for sporadic Alzheimer's disease en-code for factors that regulate glial clearance of misfolded proteins and the inflammatory reaction. External factors, including systemic inflammation and obesity are likely to interfere with the immunological processes of the brain and further promote disease progression. This re-view provides an overview on the current knowledge and focuses on the most recent and exciting findings. Modulation of risk factors and intervention with the described immune mechanisms are likely to lead to future preventive or therapeutic strategies for Alzheimer's disease.

No abstract

The observation that the T-bet transcription factor allows tissue-specific upregulation of intracellular osteopontin (Opn-i) in plasmacytoid dendritic cells (pDCs) suggests that Opn might contribute to the expression of interferon-α (IFN-α) in those cells. Here we show that Opn deficiency substantially reduced Toll-like receptor 9 (TLR9)-dependent IFN-α responses but spared expression of transcription factor NF-κB-dependent proinflammatory cytokines. Shortly after TLR9 engagement, colocalization of Opn-i and the adaptor molecule MyD88 was associated with induction of transcription factor IRF7-dependent IFN-α gene expression, whereas deficient expression of Opn-i was associated with defective nuclear translocation of IRF7 in pDCs. The importance of the Opn-IFN-α pathway was emphasized by its essential involvement in crosspresentation in vitro and in anti-herpes simplex virus 1 IFN-α response in vivo. The finding that Opn-i selectively coupled TLR9 signaling to expression of IFN-α but not to that of other proinflammatory cytokines provides new molecular insight into the biology of pDCs.Increasing evidence that innate immune responses can determine both the type and intensity of adaptive immune responses has stimulated great interest in the underlying regulatory mechanisms. The recognition phase of innate responses depends on a series of patternrecognition receptors, including Toll-like receptors (TLRs) expressed by dendritic cells (DCs), which detect a wide range of pathogen-associated molecules carried by bacteria and viruses 1 . Engagement of the TLR9 family of endosomal receptors by microbe-derived DNA triggers the production of large amounts of interferons α and β (IFN-αβ) 2 , key mediators that regulate the development of both innate and adaptive immunity [3][4][5][6] . However, the pathway initiated by TLR9 engagement that culminates in IFN-αβ production is not fully understood.

The mouse protein Qa-1 (HLA-E in humans) is essential for immunological protection and immune regulation. Although Qa-1 has been linked to CD8 T cell-dependent suppression, the physiological relevance of this observation is unclear. We generated mice deficient in Qa-1 to develop an understanding of this process. Qa-1-deficient mice develop exaggerated secondary CD4 responses to foreign and self peptides. Enhanced responses to proteolipid protein self peptide were associated with resistance of Qa-1-deficient CD4 T cells to Qa-1-restricted CD8 T suppressor activity and increased susceptibility to experimental autoimmune encephalomyelitis. These findings delineate a Qa-1-dependent T cell-T cell inhibitory interaction that prevents the pathogenic expansion of autoreactive CD4 T cell populations and consequent autoimmune disease.

SUMMARY Mechanisms that prevent inappropriate or excessive interleukin-17-producing T helper (Th17) cell responses after microbial infection may be necessary to avoid autoimmunity. Here, we define a pathway initiated by engagement of Type-I IFN receptor (IFNAR) expressed by dendritic cells (DC) that culminated in suppression of Th17 cell differentiation. IFNAR-dependent inhibition of an intracellular translational isoform of Osteopontin, termed Opn-i, de-repressed interleukin-27 (IL-27) secretion and prevented efficient Th17 responses. Moreover, Opn-i expression in DC and microglia regulated the type and intensity of Experimental Autoimmune Encephalomyelitis (EAE). Mice containing DC deficient in Opn-i produced excessive amounts of IL-27 and developed a delayed disease characterized by an enhanced Th1 response compared with the dominant Th17 response of Opn sufficient mice. Definition of the IFNAR Opn-i axis that controls Th17 development provides insight into regulation of Th sublineage development and the molecular basis of Type I interferon therapy for MS and other autoimmune diseases.

The NLRP3 inflammasome is a multiprotein complex consisting of three kinds of proteins, NLRP3, ASC, and pro-caspase-1, and plays a role in sensing pathogens and danger signals in the innate immune system. The NLRP3 inflammasome is thought to be involved in the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). However, the mechanism by which the NLRP3 inflammasome induces EAE is not clear. In this study, we found that the NLRP3 inflammasome played a critical role in inducing T-helper cell migration into the CNS. To gain migratory ability, CD4 + T cells need to be primed by NLRP3 inflammasome-sufficient antigen-presenting cells to up-regulate chemotaxis-related proteins, such as osteopontin, CCR2, and CXCR6. In the presence of the NLRP3 inflammasome, dendritic cells and macrophages also induce chemotactic ability and up-regulate chemotaxis-related proteins, such as α4β1 integrin, CCL7, CCL8, and CXCL16. On the other hand, reduced Th17 cell population size in immunized Nlrp3 −/− and Asc −/− mice is not a determinative factor for their resistance to EAE. As currently applied in clinical interventions of MS, targeting immune cell migration molecules may be an effective approach in treating MS accompanied by NLRP3 inflammasome activation.

Interferon-β (IFN-β) is widely used to treat multiple sclerosis (MS), and its efficacy was demonstrated in the setting of experimental autoimmune encephalomyelitis (EAE), an animal model of MS; however, IFN-β is not effective in treating all cases of MS. Here, we demonstrate that signaling by IFNAR (the shared receptor for IFN-α and IFN-β) on macrophages inhibits activation of Rac1 and the generation of reactive oxygen species (ROS) through suppressor of cytokine signaling 1 (SOCS1). The inhibition of Rac1 activation and ROS generation suppressed the activity of the NLRP3 inflammasome, which resulted in attenuated EAE pathogenicity. We further found that two subsets of EAE could be defined on the basis of their dependency on the NLRP3 inflammasome and that IFN-β was not an effective therapy when EAE was induced in an NLRP3 inflammasome–independent fashion. Thus, our study demonstrates a previously uncharacterized signaling pathway that is involved in the suppression of EAE by IFN-β and characterizes NLRP3-independent EAE, which cannot be treated with IFN-β.