Astrocytes have important roles in the central nervous system (CNS) during health and disease. Through genome-wide analyses we detected a transcriptional response to type I interferons (IFN-Is) in ...astrocytes during experimental CNS autoimmunity and also in CNS lesions from patients with multiple sclerosis (MS). IFN-I signaling in astrocytes reduces inflammation and experimental autoimmune encephalomyelitis (EAE) disease scores via the ligand-activated transcription factor aryl hydrocarbon receptor (AHR) and the suppressor of cytokine signaling 2 (SOCS2). The anti-inflammatory effects of nasally administered interferon (IFN)-β are partly mediated by AHR. Dietary tryptophan is metabolized by the gut microbiota into AHR agonists that have an effect on astrocytes to limit CNS inflammation. EAE scores were increased following ampicillin treatment during the recovery phase, and CNS inflammation was reduced in antibiotic-treated mice by supplementation with the tryptophan metabolites indole, indoxyl-3-sulfate, indole-3-propionic acid and indole-3-aldehyde, or the bacterial enzyme tryptophanase. In individuals with MS, the circulating levels of AHR agonists were decreased. These findings suggest that IFN-Is produced in the CNS function in combination with metabolites derived from dietary tryptophan by the gut flora to activate AHR signaling in astrocytes and suppress CNS inflammation.
Disruption of the blood-brain and blood-spinal cord barriers (BBB and BSCB, respectively) and immune cell infiltration are early pathophysiological hallmarks of multiple sclerosis (MS), its animal ...model experimental autoimmune encephalomyelitis (EAE), and neuromyelitis optica (NMO). However, their contribution to disease initiation and development remains unclear. In this study, we induced EAE in lys-eGFP-ki mice and performed single, nonterminal intravital imaging to investigate BSCB permeability simultaneously with the kinetics of GFP(+) myeloid cell infiltration. We observed a loss in BSCB integrity within a day of disease onset, which paralleled the infiltration of GFP(+) cells into the CNS and lasted for ∼4 d. Neutrophils accounted for a significant proportion of the circulating and CNS-infiltrating myeloid cells during the preclinical phase of EAE, and their depletion delayed the onset and reduced the severity of EAE while maintaining BSCB integrity. We also show that neutrophils collected from the blood or bone marrow of EAE mice transmigrate more efficiently than do neutrophils of naive animals in a BBB cell culture model. Moreover, using intravital videomicroscopy, we demonstrate that the IL-1R type 1 governs the firm adhesion of neutrophils to the inflamed spinal cord vasculature. Finally, immunostaining of postmortem CNS material obtained from an acutely ill multiple sclerosis patient and two neuromyelitis optica patients revealed instances of infiltrated neutrophils associated with regions of BBB or BSCB leakage. Taken together, our data provide evidence that neutrophils are involved in the initial events that take place during EAE and that they are intimately linked with the status of the BBB/BSCB.
Objective
Dysregulation of the blood–brain barrier (BBB) and transendothelial migration of immune cells are among the earliest central nervous system changes partaking in lesion formation in both ...multiple sclerosis (MS) and its early clinical form, the clinically isolated syndrome. Evidence for the anti‐inflammatory effects of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitors within the central nervous system arose from studies demonstrating that statins improve clinical signs in the animal model of MS and reduce the number of gadolinium‐enhancing lesions in MS.
Methods
We sought to describe the impact of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitor treatment on the physiology and immunology of human BBB‐derived endothelial cells (ECs).
Results
We demonstrate that lovastatin and simvastatin induce a 50 to 60% reduction in the diffusion rates of bovine serum albumin and 14C‐sucrose across human BBB‐ECs in vitro through abrogation of isoprenylation processes, but independent of the expression of the tight junction molecules occludin, VE‐cadherin, JAM‐1, zonula occluden‐1, and zonula occluden‐2. Simvastatin and lovastatin were equipotent in reducing BBB permeability in vitro, with median effective concentration (EC50) of 9.5 × 10−8 and 1.0 × 10−7M, respectively. We further demonstrate that lovastatin and simvastatin treatment of BBB‐ECs significantly restricts the migration of clinically isolated syndrome–derived and MS‐derived monocytes and lymphocytes across the human BBB in vitro, through a specific reduction in the secretion of the chemokines monocyte chemotactic protein‐1/CCL2 and interferon‐γ–inducible protein‐10/CXCL10 by BBB‐ECs.
Interpretation
Our data parallel the previously reported magnetic resonance imaging–based radiological findings and suggest an effect of statins that could be beneficial in early MS, restricting the diffusion of molecular tracers and the migration of immune cells across the human BBB. Ann Neurol 2006
Leukocyte transmigration into the central nervous system promotes multiple sclerosis pathogenesis, yet ambiguity remains regarding the mechanisms controlling the migration of distinct immune cell ...subsets. Using in vitro, ex vivo and postmortem human materials, we identified a significant upregulation of junctional adhesion molecule‐like expression at the blood–brain barrier, monocytes, and CD8 T cells of multiple sclerosis patients. We also detected junctional adhesion molecule‐like+ trans‐migratory cups when monocytes/CD8 T cells adhered to the blood–brain barrier, however, their migratory capacity was significantly compromised when junctional adhesion molecule‐like was blocked. These findings highlight a novel role for junctional adhesion molecule‐like in leukocyte transmigration and its potential as a promising therapeutic target.
Growing evidence supports a role for IL-1 in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), but how it impacts neuroinflammation is poorly understood. We show that ...susceptibility to EAE requires activation of IL-1R1 on radiation-resistant cells via IL-1β secreted by bone marrow-derived cells. Neutrophils and monocyte-derived macrophages (MDMs) are the main source of IL-1β and produce this cytokine as a result of their transmigration across the inflamed blood-spinal cord barrier. IL-1R1 expression in the spinal cord is found in endothelial cells (ECs) of the pial venous plexus. Accordingly, leukocyte infiltration at EAE onset is restricted to IL-1R1(+) subpial and subarachnoid vessels. In response to IL-1β, primary cultures of central nervous system ECs produce GM-CSF, G-CSF, IL-6, Cxcl1, and Cxcl2. Initiation of EAE or subdural injection of IL-1β induces a similar cytokine/chemokine signature in spinal cord vessels. Furthermore, the transfer of Gr1(+) cells on the spinal cord is sufficient to induce illness in EAE-resistant IL-1β knockout (KO) mice. Notably, transfer of Gr1(+) cells isolated from C57BL/6 mice induce massive recruitment of recipient myeloid cells compared with cells from IL-1β KO donors, and this recruitment translates into more severe paralysis. These findings suggest that an IL-1β-dependent paracrine loop between infiltrated neutrophils/MDMs and ECs drives neuroinflammation.
The blood-brain barrier (BBB) is composed of tightly bound endothelial cells (ECs) and perivascular astrocytes that regulate central nervous system (CNS) homeostasis. We showed that astrocytes ...secrete Sonic hedgehog and that BBB ECs express Hedgehog (Hh) receptors, which together promote BBB formation and integrity during embryonic development and adulthood. Using pharmacological inhibition and genetic inactivation of the Hh signaling pathway in ECs, we also demonstrated a critical role of the Hh pathway in promoting the immune quiescence of BBB ECs by decreasing the expression of proinflammatory mediators and the adhesion and migration of leukocytes, in vivo and in vitro. Overall, the Hh pathway provides a barrier-promoting effect and an endogenous anti-inflammatory balance to CNS-directed immune attacks, as occurs in multiple sclerosis.
Women develop certain autoimmune diseases more often than men. It has been hypothesized that this may relate to the development of more robust T-helper (Th)1 responses in women. To test whether women ...exhibit a Th1 bias, we isolated naïve cluster of differentiation (CD)4 ⁺ T cells from peripheral blood of healthy women and men and measured the proliferation and cytokine production by these cells in response to submaximal amounts of anti-CD3 and anti-CD28. We observed that CD4 ⁺ T cells from women produced higher levels of IFNγ as well as tended to proliferate more than male CD4 ⁺ T cells. Intriguingly, male CD4 ⁺ T cells instead had a predilection toward IL-17A production. This sex dichotomy in Th cytokine production was found to be even more striking in the Swiss/Jackson Laboratory (SJL) mouse. Studies in mice and humans indicated that the sexual dimorphism in Th1 and Th17 cytokine production was dependent on the androgen status and the T-cell expression of peroxisome proliferator activated receptor (PPAR)α and PPARγ. Androgens increased PPARα and decreased PPARγ expression by human CD4 ⁺ T cells. PPARα siRNA-mediated knockdown had the effect of increasing IFNγ by male CD4 ⁺ T cells, while transfection of CD4 ⁺ T cells with PPARγ siRNAs increased IL-17A production uniquely by female T cells. Together, our observations indicate that human T cells exhibit a sex difference in the production of IFNγ and IL-17A that may be driven by expressions of PPARα and PPARγ.
Trafficking of antigen-presenting cells into the CNS is essential for lymphocyte reactivation within the CNS compartment. Although perivascular dendritic cells found in inflammatory lesions are ...reported to polarize naive CD4+ T lymphocytes into interleukin-17-secreting-cells, the origin of those antigen-presenting cells remains controversial. We demonstrate that a subset of CD14+ monocytes migrate across the inflamed human blood–brain barrier (BBB) and differentiate into CD83+CD209+ dendritic cells under the influence of BBB-secreted transforming growth factor-β and granulocyte-macrophage colony-stimulating factor. We also demonstrate that these dendritic cells secrete interleukin-12p70, transforming growth factor-β and interleukin-6 and promote the proliferation and expansion of distinct populations of interferon-γ-secreting Th1 and interleukin-17-secreting Th17 CD4+ T lymphocytes. We further confirmed the abundance of such dendritic cells in situ, closely associated with microvascular BBB-endothelial cells within acute multiple sclerosis lesions, as well as a significant number of CD4+ interleukin-17+ T lymphocytes in the perivascular infiltrate. Our data support the notion that functional perivascular myeloid CNS dendritic cells arise as a consequence of migration of CD14+ monocytes across the human BBB, through the concerted actions of BBB-secreted transforming growth factor-β and granulocyte-macrophage colony-stimulating factor.
PDF
