Amy E. Lovett-Racke

Peroxisome Proliferator-Activated Receptor-γ Agonist 15-Deoxy-Δ12,1412,14-Prostaglandin J2 Ameliorates Experimental Autoimmune Encephalomyelitis

Peroxisome proliferator-activated receptors (PPAR) are members of a nuclear hormone receptor superfamily that includes receptors for steroids, retinoids, and thyroid hormone, all of which are known to affect the immune response. Previous studies dealing with PPAR-γ expression in the immune system have been limited. Recently, PPAR-γ was identified in monocyte/macrophage cells. In this study we examined the role of PPAR-γ in experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. The hypothesis we are testing is whether PPAR-γ plays an important role in EAE pathogenesis and whether PPAR-γ ligands can inhibit the clinical expression of EAE. Initial studies have shown that the presence of the PPAR-γ ligand 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2) inhibits the proliferation of Ag-specific T cells from the spleen of myelin basic protein Ac1–11 TCR-transgenic mice. 15d-PGJ2 suppressed IFN-γ, ΙL-10, and IL-4 production by both Con A- and myelin basic protein Ac1–11 peptide-stimulated lymphocytes as determined by ELISA and ELISPOT assay. Culture of encephalitogenic T cells with 15d-PGJ2 in the presence of Ag reduced the ability of these cells to adoptively transfer EAE. Examination of the target organ, the CNS, during the course of EAE revealed expression of PPAR-γ in the spinal cord inflammatory infiltrate. Administration of 15d-PGJ2 before and at the onset of clinical signs of EAE significantly reduced the severity of disease. These results suggest that PPAR-γ ligands may be a novel therapeutic agent for diseases such as multiple sclerosis.

Fumarates improve psoriasis and multiple sclerosis by inducing type II dendritic cells

Fumarates suppress Th1 responses by blocking IL-12 and IL-23 production by dendritic cells via distinct pathways.

T-bet Regulates the Fate of Th1 and Th17 Lymphocytes in Autoimmunity

IL-17-producing T cells (Th17) have recently been implicated in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. However, little is known about the transcription factors that regulate these cells. Although it is clear that the transcription factor T-bet plays an essential role in the differentiation of IFN-γ-producing CD4+ Th1 lymphocytes, the potential role of T-bet in the differentiation of Th17 cells is not completely understood. In this study, therapeutic administration of a small interfering RNA specific for T-bet significantly improved the clinical course of established EAE. The improved clinical course was associated with suppression of newly differentiated T cells that express IL-17 in the CNS as well as suppression of myelin basic protein-specific Th1 autoreactive T cells. Moreover, T-bet was found to directly regulate transcription of the IL-23R, and, in doing so, influenced the fate of Th17 cells, which depend on optimal IL-23 production for survival. We now show for the first time that suppression of T-bet ameliorates EAE by limiting the differentiation of autoreactive Th1 cells, as well as inhibiting pathogenic Th17 cells via regulation of IL-23R.

T-bet is essential for encephalitogenicity of both Th1 and Th17 cells.

The extent to which myelin-specific Th1 and Th17 cells contribute to the pathogenesis of experimental autoimmune encephalomyelitis (EAE) is controversial. Combinations of interleukin (IL)-1β, IL-6, and IL-23 with transforming growth factor β were used to differentiate myelin-specific T cell receptor transgenic T cells into Th17 cells, none of which could induce EAE, whereas Th1 cells consistently transferred disease. However, IL-6 was found to promote the differentiation of encephalitogenic Th17 cells. Further analysis of myelin-specific T cells that were encephalitogenic in spontaneous EAE and actively induced EAE demonstrated that T-bet expression was critical for pathogenicity, regardless of cytokine expression by the encephalitogenic T cells. These data suggest that encephalitogenicity of myelin-specific T cells appears to be mediated by a pathway dependent on T-bet and not necessarily pathway-specific end products, such as interferon γ and IL-17.

Peroxisome Proliferator-Activated Receptor α Agonists as Therapy for Autoimmune Disease

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. PPARγ ligands, which include the naturally occurring PG metabolite 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2), as well as thiazolidinediones, have been shown to have anti-inflammatory activity. The PPARα agonists, gemfibrozil, ciprofibrate, and fenofibrate, have an excellent track history as oral agents used to treat hypertriglyceridemia. In the present study, we demonstrate that these PPARα agonists can increase the production of the Th2 cytokine, IL-4, and suppress proliferation by TCR transgenic T cells specific for the myelin basic protein Ac1–11, as well as reduce NO production by microglia. Oral administration of gemfibrozil and fenofibrate inhibited clinical signs of experimental autoimmune encephalomyelitis. More importantly, gemfibrozil was shown to shift the cytokine secretion of human T cell lines by inhibiting IFN-γ and promoting IL-4 secretion. These results suggest that PPARα agonists such as gemfibrozil and fenofibrate, may be attractive candidates for use in human inflammatory conditions such as multiple sclerosis.

Glatiramer acetate (Copaxone) therapy induces CD8+ T cell responses in patients with multiple sclerosis

Glatiramer acetate (GA; Copaxone) is a random copolymer of glutamic acid, lysine, alanine, and tyrosine that is used therapeutically in patients with multiple sclerosis (MS). To investigate the mechanism of the drugs immunomodulatory effect, we used immunophenotypic approaches to characterize the precise nature of GA-induced T cell responses. We demonstrate here that healthy individuals and untreated MS patients exhibit prominent T cell proliferative responses to GA. However, these responses are different in distinct subsets of T cells. Whereas GA-induced CD4(+) T cell responses are comparable in healthy individuals and MS patients, CD8(+) T cell responses are significantly lower in untreated MS patients. Treatment with GA results in upregulation of these CD8(+) responses with restoration to levels observed in healthy individuals. Both CD4(+) and CD8(+) GA-specific responses are HLA-restricted. GA therapy also induces a change in the cytokine profile of GA-specific CD4(+) and CD8(+) T cells. This study provides the first direct immunophenotypic evidence, to our knowledge, of GA-specific CD8(+) T cell responses and their upregulation during the course of therapy, which may suggest a role for these responses in the immunomodulatory effects of the drug.

Th1 versus Th17: are T cell cytokines relevant in multiple sclerosis?

Our understanding of the pathophysiology of multiple sclerosis (MS) has evolved significantly over the past two decades as the fields of immunology and neurobiology provide new avenues of exploration into the cause and mechanism of the disease. It has been known for decades that T cells have different cytokine phenotypes, yet the cytokine phenotype of pathogenic T cells in MS is still an area of debate. In EAE, it appears that IFNγ and IL-17, produced by Th1 and Th17 cells respectively, are not the critical factor that determines T cell encephalitogenicity. However, there are molecules such as IL-23, T-bet and STAT4, that appear to be critical, yet it is unclear whether all these molecules contribute to a common, yet undefined pathway, or act in a synergistic manner which culminates in encephalitogenicity has still to be determined. Therefore, the focus of research on effector T cells in MS should focus on pathways upstream of the cytokines that define Th1 and Th17 cells, since downstream products, such as IFNγ and IL-17, probably are not critical determinants of whether an effector T cells is capable of trafficking to the CNS and inducing inflammatory demyelination.

Micro-RNA dysregulation in multiple sclerosis favours pro-inflammatory T-cell-mediated autoimmunity

Pro-inflammatory T cells mediate autoimmune demyelination in multiple sclerosis. However, the factors driving their development and multiple sclerosis susceptibility are incompletely understood. We investigated how micro-RNAs, newly described as post-transcriptional regulators of gene expression, contribute to pathogenic T-cell differentiation in multiple sclerosis. miR-128 and miR-27b were increased in naïve and miR-340 in memory CD4(+) T cells from patients with multiple sclerosis, inhibiting Th2 cell development and favouring pro-inflammatory Th1 responses. These effects were mediated by direct suppression of B lymphoma Mo-MLV insertion region 1 homolog (BMI1) and interleukin-4 (IL4) expression, resulting in decreased GATA3 levels, and a Th2 to Th1 cytokine shift. Gain-of-function experiments with these micro-RNAs enhanced the encephalitogenic potential of myelin-specific T cells in experimental autoimmune encephalomyelitis. In addition, treatment of multiple sclerosis patient T cells with oligonucleotide micro-RNA inhibitors led to the restoration of Th2 responses. These data illustrate the biological significance and therapeutic potential of these micro-RNAs in regulating T-cell phenotypes in multiple sclerosis.

The mechanism of action of glatiramer acetate treatment in multiple sclerosis

Objective: Glatiramer acetate (formerly known as copolymer 1) is the major noninterferon immunomodulatory agent used in the treatment of relapsing-remitting multiple sclerosis. Its mechanism of action over the past 40 years has evolved with our understanding of the immune response. Methods: We review the various mechanisms that have been proposed for this random polymer over the years, with emphasis on recent methods that utilize modern immunologic techniques. Results: Studies describing processes such as immune deviation and effects on regulatory T cells and antigen-presenting cells are presented. Conclusions: Effects of glatiramer acetate on the immune response have evolved as our technical abilities and knowledge of the immune response itself have developed.

miR-29ab1 deficiency identifies a negative feedback loop controlling Th1 bias that is dysregulated in multiple sclerosis.

Th cell programming and function is tightly regulated by complex biological networks to prevent excessive inflammatory responses and autoimmune disease. The importance of microRNAs (miRNAs) in this process is highlighted by the preferential Th1 polarization of Dicer-deficient T cells that lack miRNAs. Using genetic knockouts, we demonstrate that loss of endogenous miR-29, derived from the miR-29ab1 genomic cluster, results in unrestrained T-bet expression and IFN-γ production. miR-29b regulates T-bet and IFN-γ via a direct interaction with the 3′ untranslated regions, and IFN-γ itself enhances miR-29b expression, establishing a novel regulatory feedback loop. miR-29b is increased in memory CD4+ T cells from multiple sclerosis (MS) patients, which may reflect chronic Th1 inflammation. However, miR-29b levels decrease significantly upon T cell activation in MS patients, suggesting that this feedback loop is dysregulated in MS patients and may contribute to chronic inflammation. miR-29 thus serves as a novel regulator of Th1 differentiation, adding to the understanding of T cell-intrinsic regulatory mechanisms that maintain a balance between protective immunity and autoimmunity.