Luisa Klotz

The nuclear receptor PPARγ selectively inhibits Th17 differentiation in a T cell–intrinsic fashion and suppresses CNS autoimmunity

T helper cells secreting interleukin (IL)-17 (Th17 cells) play a crucial role in autoimmune diseases like multiple sclerosis (MS). Th17 differentiation, which is induced by a combination of transforming growth factor (TGF)-β/IL-6 or IL-21, requires expression of the transcription factor retinoic acid receptor–related orphan receptor γt (RORγt). We identify the nuclear receptor peroxisome proliferator–activated receptor γ (PPARγ) as a key negative regulator of human and mouse Th17 differentiation. PPARγ activation in CD4+ T cells selectively suppressed Th17 differentiation, but not differentiation into Th1, Th2, or regulatory T cells. Control of Th17 differentiation by PPARγ involved inhibition of TGF-β/IL-6–induced expression of RORγt in T cells. Pharmacologic activation of PPARγ prevented removal of the silencing mediator for retinoid and thyroid hormone receptors corepressor from the RORγt promoter in T cells, thus interfering with RORγt transcription. Both T cell–specific PPARγ knockout and endogenous ligand activation revealed the physiological role of PPARγ for continuous T cell–intrinsic control of Th17 differentiation and development of autoimmunity. Importantly, human CD4+ T cells from healthy controls and MS patients were strongly susceptible to PPARγ-mediated suppression of Th17 differentiation. In summary, we report a PPARγ-mediated T cell–intrinsic molecular mechanism that selectively controls Th17 differentiation in mice and in humans and that is amenable to pharmacologic modulation. We therefore propose that PPARγ represents a promising molecular target for specific immunointervention in Th17-mediated autoimmune diseases such as MS.

Gut microbiota from multiple sclerosis patients enables spontaneous autoimmune encephalomyelitis in mice

Significance Studies using experimental models have indicated that multiple sclerosis (MS)-like disease can be triggered in the gut following interactions of brain autoimmune T lymphocytes with local microbiota. Here we studied the gut microbiota from monozygotic human twin pairs discordant for multiple sclerosis. When we transferred human-derived microbiota into transgenic mice expressing a myelin autoantigen-specific T cell receptor, we found that gut microbiota from multiple sclerosis-affected twins induced CNS-specific autoimmunity at a higher incidence than microbiota from healthy co-twins. Our results offer functional evidence that human microbiome components contribute to CNS-specific autoimmunity. There is emerging evidence that the commensal microbiota has a role in the pathogenesis of multiple sclerosis (MS), a putative autoimmune disease of the CNS. Here, we compared the gut microbial composition of 34 monozygotic twin pairs discordant for MS. While there were no major differences in the overall microbial profiles, we found a significant increase in some taxa such as Akkermansia in untreated MS twins. Furthermore, most notably, when transplanted to a transgenic mouse model of spontaneous brain autoimmunity, MS twin-derived microbiota induced a significantly higher incidence of autoimmunity than the healthy twin-derived microbiota. The microbial profiles of the colonized mice showed a high intraindividual and remarkable temporal stability with several differences, including Sutterella, an organism shown to induce a protective immunoregulatory profile in vitro. Immune cells from mouse recipients of MS-twin samples produced less IL-10 than immune cells from mice colonized with healthy-twin samples. IL-10 may have a regulatory role in spontaneous CNS autoimmunity, as neutralization of the cytokine in mice colonized with healthy-twin fecal samples increased disease incidence. These findings provide evidence that MS-derived microbiota contain factors that precipitate an MS-like autoimmune disease in a transgenic mouse model. They hence encourage the detailed search for protective and pathogenic microbial components in human MS.

Immune mechanisms of new therapeutic strategies in multiple sclerosis-A focus on alemtuzumab.

Alemtuzumab is a humanized monoclonal antibody targeting CD52, a broadly expressed cell surface molecule on immune cells. Application results in a rapid and long-lasting removal of lymphocyte populations from the circulation. Alemtuzumab-treatment of MS patients with relapsing-remitting forms of the disease significantly reduced the risk of relapse and accumulation of disability compared to interferon β-1a treatment in a phase II trial. Interestingly, further analysis together with parallel experimental studies suggested that alemtuzumab not only reduces disease activity due to its immune cell-depleting effect, but also confers neuroprotective effects, presumably by inducing production of neurotrophic factors in autoreactive T cells. However, alemtuzumab-treated MS patients experienced increased rates of novel autoimmunity and a slight increase in infections, demonstrating that alemtuzumab-mediated skewing of the immune cell compartment has a broad influence on immune functions. This review discusses the current concepts about the underlying mechanisms causing these altered immune responses in alemtuzumab-treated MS patients.

Sodium chloride promotes pro-inflammatory macrophage polarization thereby aggravating CNS autoimmunity

The increasing incidence in Multiple Sclerosis (MS) during the last decades in industrialized countries might be linked to a change in dietary habits. Nowadays, enhanced salt content is an important characteristic of Western diet and increased dietary salt (NaCl) intake promotes pathogenic T cell responses contributing to central nervous system (CNS) autoimmunity. Given the importance of macrophage responses for CNS disease propagation, we addressed the influence of salt consumption on macrophage responses in CNS autoimmunity. We observed that EAE-diseased mice receiving a NaCl-high diet showed strongly enhanced macrophage infiltration and activation within the CNS accompanied by disease aggravation during the effector phase of EAE. NaCl treatment of macrophages elicited a strong pro-inflammatory phenotype characterized by enhanced pro-inflammatory cytokine production, increased expression of immune-stimulatory molecules, and an antigen-independent boost of T cell proliferation. This NaCl-induced pro-inflammatory macrophage phenotype was accompanied by increased activation of NF-kB and MAPK signaling pathways. The pathogenic relevance of NaCl-conditioned macrophages is illustrated by the finding that transfer into EAE-diseased animals resulted in significant disease aggravation compared to untreated macrophages. Importantly, also in human monocytes, NaCl promoted a pro-inflammatory phenotype that enhanced human T cell proliferation. Taken together, high dietary salt intake promotes pro-inflammatory macrophages that aggravate CNS autoimmunity. Together with other studies, these results underline the need to further determine the relevance of increased dietary salt intake for MS disease severity.

Dimethyl fumarate treatment alters circulating T helper cell subsets in multiple sclerosis

Objective: To evaluate the effect of dimethyl fumarate (DMF; Tecfidera, Biogen, Weston, MA) on CD4+ and CD8+ T cell subsets in patients with multiple sclerosis (MS). Methods: Peripheral lymphocyte subsets, including CD4+ and CD8+ memory cells and T helper (TH) cells TH1, TH2, TH17, and peripheral regulatory T cell (pTreg) subpopulations were analyzed before and 6 months after onset of DMF treatment. Results: CD4+ and CD8+ memory T cells were preferentially decreased compared to naive CD4+ and CD8+ T cell populations. Within the CD4+ memory T cell population, frequencies of TH1 cells were decreased, whereas those of TH2 cells were increased and those of TH17 cells remained unaltered. Accordingly, we observed decreased production of interferon γ, granulocyte-macrophage colony-stimulating factor, tumor necrosis factor α, and interleukin (IL)-22 by CD4+ T cells under DMF treatment, whereas the frequency of IL-4- and IL-17A-producing CD4+ T cells remained unchanged. With regard to regulatory T cells, proportions of pTreg increased following DMF treatment. Conclusion: Our data demonstrate that DMF treatment of patients with MS affects predominantly memory T cells accompanied by a shift in TH cell populations, resulting in a shift toward anti-inflammatory responses. These findings indicate that monitoring of memory subsets might enhance vigilance of impaired antiviral immunity and that patients with TH1-driven disease might preferentially benefit from DMF treatment. Classification of Evidence: This study provides Class IV evidence that DMF might preferentially reduce CD4+ and CD8+ memory T cells in MS.

Salt-dependent chemotaxis of macrophages

Besides their role in immune system host defense, there is growing evidence that macrophages may also be important regulators of salt homeostasis and blood pressure by a TonEBP-VEGF-C dependent buffering mechanism. As macrophages are known to accumulate in the skin of rats fed under high salt diet conditions and are pivotal for removal of high salt storage, the question arose how macrophages sense sites of high sodium storage. Interestingly, we observed that macrophage-like RAW264.7 cells, murine bone marrow-derived macrophages and peritoneal macrophages recognize NaCl hypertonicity as a chemotactic stimulus and migrate in the direction of excess salt concentration by using an in vitro transwell migration assay. While RAW264.7 cells migrated toward NaCl in a dose-dependent fashion, no migratory response toward isotonic or hypotonic media controls, or other osmo-active agents, e.g. urea or mannitol, could be detected. Interestingly, we could not establish a specific role of the osmoprotective transcription factor TonEBP in regulating salt-dependent chemotaxis, since the specific migration of bone marrow-derived macrophages following RNAi of TonEBP toward NaCl was not altered. Although the underlying mechanism remains unidentified, these data point to a thus far unappreciated role for NaCl-dependent chemotaxis of macrophages in the clearance of excess salt, and suggest the existence of novel NaCl sensor/effector circuits, which are independent of the TonEBP system.

CC chemokine receptor 4 is required for experimental autoimmune encephalomyelitis by regulating GM-CSF and IL-23 production in dendritic cells

Dendritic cells (DCs) are pivotal for the development of experimental autoimmune encephalomyelitis (EAE). However, the mechanisms by which they control disease remain to be determined. This study demonstrates that expression of CC chemokine receptor 4 (CCR4) by DCs is required for EAE induction. CCR4−/− mice presented enhanced resistance to EAE associated with a reduction in IL-23 and GM-CSF expression in the CNS. Restoring CCR4 on myeloid cells in bone marrow chimeras or intracerebral microinjection of CCR4-competent DCs, but not macrophages, restored EAE in CCR4−/− mice, indicating that CCR4+ DCs are cellular mediators of EAE development. Mechanistically, CCR4−/− DCs were less efficient in GM-CSF and IL-23 production and also TH-17 maintenance. Intraspinal IL-23 reconstitution restored EAE in CCR4−/− mice, whereas intracerebral inoculation using IL-23−/− DCs or GM-CSF−/− DCs failed to induce disease. Thus, CCR4-dependent GM-CSF production in DCs required for IL-23 release in these cells is a major component in the development of EAE. Our study identified a unique role for CCR4 in regulating DC function in EAE, harboring therapeutic potential for the treatment of CNS autoimmunity by targeting CCR4 on this specific cell type.

Fingolimod treatment promotes regulatory phenotype and function of B cells

To evaluate the influence of Fingolimod treatment on B‐cell subset composition and function in multiple sclerosis patients and its potential clinical relevance.

Blood coagulation factor XII drives adaptive immunity during neuroinflammation via CD87-mediated modulation of dendritic cells

Aberrant immune responses represent the underlying cause of central nervous system (CNS) autoimmunity, including multiple sclerosis (MS). Recent evidence implicated the crosstalk between coagulation and immunity in CNS autoimmunity. Here we identify coagulation factor XII (FXII), the initiator of the intrinsic coagulation cascade and the kallikrein–kinin system, as a specific immune cell modulator. High levels of FXII activity are present in the plasma of MS patients during relapse. Deficiency or pharmacologic blockade of FXII renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by reduced numbers of interleukin-17A-producing T cells. Immune activation by FXII is mediated by dendritic cells in a CD87-dependent manner and involves alterations in intracellular cyclic AMP formation. Our study demonstrates that a member of the plasmatic coagulation cascade is a key mediator of autoimmunity. FXII inhibition may provide a strategy to combat MS and other immune-related disorders.

Impaired NK-mediated regulation of T-cell activity in multiple sclerosis is reconstituted by IL-2 receptor modulation

Significance The importance of natural killer (NK) cells in the control of autoimmunity has recently attracted considerable attention. The current study revealed NK cells as additional players in controlling T-cell activity in CNS autoimmunity. NK-mediated control of T-cell activity in multiple sclerosis (MS) is dysregulated and caused by impaired DNAX accessory molecule-1/CD155 interaction between NK cells and CD4+ T cells. Therapeutic immune modulation of the IL-2 receptor with daclizumab, which has just successfully passed a phase III study in relapsing-remitting MS, not only enhances the cytolytic activity of NK cells but also restores defective NK-mediated immune regulation by increasing the proportion of CD155-expressing CD4+ T cells, thus rendering CD4+ T cells most likely more sensitive to NK-mediated lysis. Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system (CNS) resulting from a breakdown in peripheral immune tolerance. Although a beneficial role of natural killer (NK)-cell immune-regulatory function has been proposed, it still needs to be elucidated whether NK cells are functionally impaired as part of the disease. We observed NK cells in active MS lesions in close proximity to T cells. In accordance with a higher migratory capacity across the blood–brain barrier, CD56bright NK cells represent the major intrathecal NK-cell subset in both MS patients and healthy individuals. Investigating the peripheral blood and cerebrospinal fluid of MS patients treated with natalizumab revealed that transmigration of this subset depends on the α4β1 integrin very late antigen (VLA)-4. Although no MS-related changes in the migratory capacity of NK cells were observed, NK cells derived from patients with MS exhibit a reduced cytolytic activity in response to antigen-activated CD4+ T cells. Defective NK-mediated immune regulation in MS is mainly attributable to a CD4+ T-cell evasion caused by an impaired DNAX accessory molecule (DNAM)-1/CD155 interaction. Both the expression of the activating NK-cell receptor DNAM-1, a genetic alteration consistently found in MS-association studies, and up-regulation of the receptor’s ligand CD155 on CD4+ T cells are reduced in MS. Therapeutic immune modulation of IL-2 receptor restores impaired immune regulation in MS by increasing the proportion of CD155-expressing CD4+ T cells and the cytolytic activity of NK cells.