Experimental autoimmune encephalomyelitis (EAE) is the most commonly used experimental model for the human inflammatory demyelinating disease, multiple sclerosis (MS). EAE is a complex condition in which the interaction between a variety of immunopathological and neuropathological mechanisms leads to an approximation of the key pathological features of MS: inflammation, demyelination, axonal loss and gliosis. The counter-regulatory mechanisms of resolution of inflammation and remyelination also occur in EAE, which, therefore can also serve as a model for these processes. Moreover, EAE is often used as a model of cell-mediated organ-specific autoimmune conditions in general. EAE has a complex neuropharmacology, and many of the drugs that are in current or imminent use in MS have been developed, tested or validated on the basis of EAE studies. There is great heterogeneity in the susceptibility to the induction, the method of induction and the response to various immunological or neuropharmacological interventions, many of which are reviewed here. This makes EAE a very versatile system to use in translational neuro-and immunopharmacology, but the model needs to be tailored to the scientific question being asked. While creating difficulties and underscoring the inherent weaknesses of this model of MS in straightforward translation from EAE to the human disease, this variability also creates an opportunity to explore multiple facets of the immune and neural mechanisms of immune-mediated neuroinflammation and demyelination as well as intrinsic protective mechanisms. This allows the eventual development and preclinical testing of a wide range of potential therapeutic interventions. LINKED ARTICLESThis article is part of a themed issue on Translational Neuropharmacology. To view the other articles in this issue visit http://dx.doi.org/10. 1111/bph.2011.164.issue-4 Abbreviations ADEM, acute disseminated encephalomyelitis; ADNP, activity dependent neuroprotective protein; AHR, aryl hydrocarbon receptor; APC, antigen-presenting cells; APL, altered peptide ligand; AT, adoptive transfer; C1 and CB2 receptors, cannabinoid receptors 1 and 2; CIS, clinically isolated syndrome; CNS, central nervous system; DA, dark agouti; DMT, disease-modifying treatment; EAE, experimental autoimmune (allergic) encephalomyelitis; EAN, experimental autoimmune (allergic) neuritis; EBV, Epstein-Barr virus; GA, glatiramer acetate; IFN, interferon; IL, interleukin; IL-1RA, interleukin 1 receptor antagonist; JCV, John Cunningham virus; MBP, myelin basic protein; MOG, myelin oligodendrocyte glycoprotein; MRI, magnetic resonance imaging; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; NABT, normal appearing brain tissue; NAWM, normal appearing white matter; NMO, neuromyelitis optica; NK1 receptor, neurokinin 1 receptor; PGE, prostaglandin E; PLP, proteolipid protein; PP, primary progressive; PR, progressive relapsing; ROR, retinoid orphan receptor; RR, relapsing-remitting; SP, secondary progressive; TCR, T-cell receptor; TGF, transforming growth...

Recently the rationale for combining targeted therapy with immunotherapy has come to light, but our understanding of the immune response during MAPK pathway inhibitor treatment is limited. We discovered that the immune-microenvironment can act as source of resistance to MAPK pathway-targeted therapy, and moreover during treatment this source becomes reinforced. In particular, we identified macrophage-derived TNFα as a crucial melanoma-growth factor that provides resistance to MAPK pathway inhibitors through the lineage-transcription factor MITF. Most strikingly, in BRAF mutant melanomas of patients and BRafV600E-melanoma allografts MAPK pathway inhibitors increased the number of tumor-associated macrophages, and TNFα and MITF expression. Inhibiting TNFα-signaling with IκB-kinase inhibitors profoundly enhanced the efficacy of MAPK pathway inhibitors by targeting not only the melanoma cells, but also the microenvironment. In summary, we identify the immune-microenvironment as a novel source of resistance and reveal a new strategy to improve the efficacy of targeted therapy in melanoma.

Naturally occurring CD4+CD25+FOXP3+ regulatory T cells suppress the activity of pathogenic T cells and prevent development of autoimmune responses. There is growing evidence that TLRs are involved in modulating regulatory T cell (Treg) functions both directly and indirectly. Specifically, TLR2 stimulation has been shown to reduce the suppressive function of Tregs by mechanisms that are incompletely understood. The developmental pathways of Tregs and Th17 cells are considered divergent and mutually inhibitory, and IL-17 secretion has been reported to be associated with reduced Treg function. We hypothesized that TLR2 stimulation may reduce the suppressive function of Tregs by regulating the balance between Treg and Th17 phenotype and function. We examined the effect of different TLR2 ligands on the suppressive functions of Tregs and found that activation of TLR1/2 heterodimers reduces the suppressive activity of CD4+CD25hiFOXP3lowCD45RA+ (naive) and CD4+CD25hiFOXP3hiCD45RA− (memory or effector) Treg subpopulations on CD4+CD25−FOXP3−CD45RA+ responder T cell proliferation while at the same time enhancing the secretion of IL-6 and IL-17, increasing RORC, and decreasing FOXP3 expression. Neutralization of IL-6 or IL-17 abrogated Pam3Cys-mediated reduction of Treg suppressive function. We also found that, in agreement with recent observations in mouse T cells, TLR2 stimulation can promote Th17 differentiation of human T helper precursors. We conclude that TLR2 stimulation, in combination with TCR activation and costimulation, promotes the differentiation of distinct subsets of human naive and memory/effector Tregs into a Th17-like phenotype and their expansion. Such TLR-induced mechanism of regulation of Treg function could enhance microbial clearance and increase the risk of autoimmune reactions.

Osteoarthritis (OA) is a multifactorial, often progressive, painful disease. OA often progresses with an apparent irreversible loss of articular cartilage, exposing underlying bone, resulting in pain and loss of mobility. This cartilage loss is thought to be permanent due to ineffective repair and apparent lack of stem/progenitor cells in that tissue. However, the adjacent synovial lining and synovial fluid are abundant with mesenchymal progenitor/stem cells (synovial mesenchymal progenitor cells [sMPCs]) capable of differentiating into cartilage both in vitro and in vivo. Previous studies have demonstrated that MPCs can home to factors such as monocyte chemotactic protein 1 (MCP‐1/CCL2) expressed after injury. While MCP‐1 (and its corresponding receptors) appears to play a role in recruiting stem cells to the site of injury, in this study, we have demonstrated that MCP‐1 is upregulated in OA synovial fluid and that exposure to MCP‐1 activates sMPCs, while concurrently inhibiting these cells from undergoing chondrogenesis in vitro. Furthermore, exposure to physiological (OA knee joint synovial fluid) levels of MCP‐1 triggers changes in the transcriptome of sMPCs and prolonged exposure to the chemokine induces the expression of MCP‐1 in sMPCs, resulting in a positive feedback loop from which sMPCs cannot apparently escape. Therefore, we propose a model where MCP‐1 (normally expressed after joint injury) recruits sMPCs to the area of injury, but concurrently triggers changes in sMPC transcriptional regulation, leading to a blockage in the chondrogenic program. These results may open up new avenues of research into the lack of endogenous repair observed after articular cartilage injury and/or arthritis. Stem Cells 2013;31:2253–2265

Summary Background The coagulation cascade has been shown to participate in chronic liver injury and fibrosis, but the contribution of various thrombin targets, such as protease activated receptors (PARs) and fibrin(ogen), has not been fully described. Emerging evidence suggests that in some experimental settings of chronic liver injury, platelets can promote liver repair and inhibit liver fibrosis. However, the precise mechanisms linking coagulation and platelet function to hepatic tissue changes following injury remain poorly defined. Objectives To determine the role of PAR-4, a key thrombin receptor on mouse platelets, and fibrin(ogen) engagement of the platelet αIIbβ3 integrin in a model of cholestatic liver injury and fibrosis. Methods Biliary and hepatic injury was characterized following 4 week administration of the bile duct toxicant α-naphthylisothiocyanate (ANIT) (0.025%) in PAR-4-deficient mice (PAR-4−/− mice), mice expressing a mutant form of fibrin(ogen) incapable of binding integrin αIIbβ3 (FibγΔ5), and wild-type mice. Results Elevated plasma thrombin-antithrombin and serotonin levels, hepatic fibrin deposition and platelet accumulation in liver accompanied hepatocellular injury and fibrosis in ANIT-treated wild-type mice. PAR-4 deficiency reduced plasma serotonin levels, increased serum bile acid concentration, and exacerbated ANIT-induced hepatocellular injury and peribiliary fibrosis. Compared to PAR-4-deficient mice, ANIT-treated FibγΔ5 mice displayed more widespread hepatocellular necrosis accompanied by marked inflammation, robust fibroblast activation and extensive liver fibrosis. Conclusions Collectively, the results indicate that PAR-4 and fibrin-αIIbβ3 integrin engagement, pathways coupling coagulation to platelet activation, each exert hepatoprotective effects during chronic cholestasis.

During obstructive cholestasis, increased concentrations of bile acids activate ERK1/2 in hepatocytes, which up-regulates early growth response factor 1, a key regulator of proinflammatory cytokines, such as macrophage inflammatory protein 2 (MIP-2), which, in turn, exacerbates cholestatic liver injury. Recent studies have indicated that IL-17A contributes to hepatic inflammation during obstructive cholestasis, suggesting that bile acids and IL-17A may interact to regulate hepatic inflammatory responses. We treated mice with an IL-17A neutralizing antibody or control IgG and subjected them to bile duct ligation. Neutralization of IL-17A prevented up-regulation of proinflammatory cytokines, hepatic neutrophil accumulation, and liver injury, indicating an important role for IL-17A in neutrophilic inflammation during cholestasis. Treatment of primary mouse hepatocytes with taurocholic acid (TCA) increased the expression of MIP-2. Co-treatment with IL-17A synergistically enhanced up-regulation of MIP-2 by TCA. In contrast to MIP-2, IL-17A did not affect up-regulation of Egr-1 by TCA, indicating that IL-17A does not affect bile acid-induced activation of signaling pathways upstream of early growth response factor 1. In addition, bile acids increased expression of IL-23, a key regulator of IL-17A production in hepatocytes in vitro and in vivo. Collectively, these data identify bile acids as novel triggers of the IL-23/IL-17A axis and suggest that IL-17A promotes hepatic inflammation during cholestasis by synergistically enhancing bile acid-induced production of proinflammatory cytokines by hepatocytes.

Background: Macrophages are important targets and long-lived reservoirs of HIV-1, which are not cleared of infection by currently available treatments. In the primary monocyte-derived macrophage model of infection, replication is initially productive followed by a decline in virion output over ensuing weeks, coincident with a decrease in the levels of the essential viral transactivator protein Tat. We investigated two possible mechanisms in macrophages for regulation of viral replication, which appears to be primarily regulated at the level of tat mRNA: 1) differential mRNA stability, used by cells and some viruses for the rapid regulation of gene expression and 2) control of HIV-1 alternative splicing, which is essential for optimal viral replication.

Recent research has demonstrated that infection with the bacterial pathogen Helicobacter pylori is less common amongst patients with multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). We aimed to compare the prevalence of H. pylori amongst MS patients and healthy controls, and also investigated the impact of this infection on an animal model for MS, experimental autoimmune encephalomyelitis (EAE). The H. pylori status of 71 MS patients and 42 healthy controls was determined by serology. Groups of C57BL/6 mice were infected with H. pylori, or given diluent alone as a placebo, prior to inducing EAE. Clinical scores were assessed for all mice, and spleens and spinal cord tissue were harvested. CD4+ T cell subsets were quantified by flow cytometry, and T cell proliferation assays were performed. In MS patients the seroprevalence of H. pylori was half that of healthy controls (p = 0.018). Over three independent experiments, prior H. pylori infection had a moderate effect in reducing the severity of EAE (p = 0.012). In line with this, the antigen-specific T cell proliferative responses of infected animals were significantly reduced (p = 0.001), and there was a fourfold reduction in the number of CD4+ cells in the CNS. CD4+ populations in both the CNS and the spleens of infected mice also contained greatly reduced proportions of IFNγ+, IL-17+, T-bet+, and RORγt+ cells, but the proportions of Foxp3+ cells were equivalent. There were no differences in the frequency of splenic CD4+cells expressing markers of apoptosis between infected and uninfected animals. H. pylori was less prevalent amongst MS patients. In mice, the infection exerted some protection against EAE, inhibiting both Th1 and Th17 responses. This could not be explained by the presence of increased numbers of Foxp3+ regulatory T cells, or T cell apoptosis. This is the first direct experimental evidence showing that H. pylori may provide protection against inflammatory demyelination in the CNS.