T-Cell-Intrinsic Receptor Interacting Protein 2 Regulates Pathogenic T Helper 17 Cell Differentiation.

Receptor interacting protein 2 (RIP2) plays a role in sensing intracellular pathogens, but its function in T cells is unclear. We show that RIP2 deficiency in CD4+ T cells resulted in chronic and severe interleukin-17A-mediated inflammation during Chlamydia pneumoniae lung infection, increased T helper 17 (Th17) cell formation in lungs of infected mice, accelerated atherosclerosis, and more severe experimental autoimmune encephalomyelitis. While RIP2 deficiency resulted in reduced conventional Th17 cell differentiation, it led to significantly enhanced differentiation of pathogenic (p)Th17 cells, which was dependent on RORα transcription factor and interleukin-1 but independent of nucleotide oligomerization domain (NOD) 1 and 2. Overexpression of RIP2 resulted in suppression of pTh17 cell differentiation, an effect mediated by its CARD domain, and phenocopied by a cell-permeable RIP2 CARD peptide. Our data suggest that RIP2 has a T cell-intrinsic role in determining the balance between homeostatic and pathogenic Th17 cell responses.

RAS P21 Protein Activator 3 (RASA3) Specifically Promotes Pathogenic T Helper 17 Cell Generation by Repressing T-Helper-2-Cell-Biased Programs.

Pathogenic Th17 (pTh17) cells drive inflammation and immune-pathology, but whether pTh17 cells are a Th17 cell subset whose generation is under specific molecular control remains unaddressed. We found that Ras p21 protein activator 3 (RASA3) was highly expressed by pTh17 cells relative to non-pTh17 cells and was required specifically for pTh17 generation in vitro and in vivo. Mice conditionally deficient for Rasa3 in T cells showed less pathology during experimental autoimmune encephalomyelitis. Rasa3-deficient T cells acquired a Th2 cell-biased program that dominantly trans-suppressed pTh17 cell generation via interleukin 4 production. The Th2 cell bias of Rasa3-deficient T cells was due to aberrantly elevated transcription factor IRF4 expression. RASA3 promoted proteasome-mediated IRF4 protein degradation by facilitating interaction of IRF4 with E3-ubiquitin ligase Cbl-b. Therefore, a RASA3-IRF4-Cbl-b pathway specifically directs pTh17 cell generation by balancing reciprocal Th17-Th2 cell programs. These findings indicate that a distinct molecular program directs pTh17 cell generation and reveals targets for treating pTh17 cell-related pathology and diseases.

Short, but Smart: SCFAs Train T Cells in the Gut to Fight Autoimmunity in the Brain.

In this issue of Immunity, Haghikia and colleagues (2015) demonstrate that dietary fatty acids, by modulating gut microbes and their metabolism, regulate mucosal immune cells to impact systemic immunity. Using this mechanism, dietary and bacteria-derived medium-chain and long-chain fatty acids exacerbate, whereas short-chain fatty acids ameliorate, autoimmunity in the brain.

Dietary Fatty Acids Directly Impact Central Nervous System Autoimmunity via the Small Intestine.

Growing empirical evidence suggests that nutrition and bacterial metabolites might impact the systemic immune response in the context of disease and autoimmunity. We report that long-chain fatty acids (LCFAs) enhanced differentiation and proliferation of T helper 1 (Th1) and/or Th17 cells and impaired their intestinal sequestration via p38-MAPK pathway. Alternatively, dietary short-chain FAs (SCFAs) expanded gut T regulatory (Treg) cells by suppression of the JNK1 and p38 pathway. We used experimental autoimmune encephalomyelitis (EAE) as a model of T cell-mediated autoimmunity to show that LCFAs consistently decreased SCFAs in the gut and exacerbated disease by expanding pathogenic Th1 and/or Th17 cell populations in the small intestine. Treatment with SCFAs ameliorated EAE and reduced axonal damage via long-lasting imprinting on lamina-propria-derived Treg cells. These data demonstrate a direct dietary impact on intestinal-specific, and subsequently central nervous system-specific, Th cell responses in autoimmunity, and thus might have therapeutic implications for autoimmune diseases such as multiple sclerosis.

IFP35 family proteins promote neuroinflammation and multiple sclerosis.

Excessive activation of T cells and microglia represents a hallmark of the pathogenesis of human multiple sclerosis (MS). However, the regulatory molecules overactivating these immune cells remain to be identified. Previously, we reported that extracellular IFP35 family proteins, including IFP35 and NMI, activated macrophages as proinflammatory molecules in the periphery. Here, we investigated their functions in the process of neuroinflammation both in the central nervous system (CNS) and the periphery. Our analysis of clinical transcriptomic data showed that expression of IFP35 family proteins was up-regulated in patients with MS. Additional in vitro studies demonstrated that IFP35 and NMI were released by multiple cells. IFP35 and NMI subsequently triggered nuclear factor kappa B-dependent activation of microglia via the TLR4 pathway. Importantly, we showed that both IFP35 and NMI activated dendritic cells and promoted naïve T cell differentiation into Th1 and Th17 cells. Nmi-/- , Ifp35-/- , or administration of neutralizing antibodies against IFP35 alleviated the immune cells' infiltration and demyelination in the CNS, thus reducing the severity of experimental autoimmune encephalomyelitis. Together, our findings reveal a hitherto unknown mechanism by which IFP35 family proteins facilitate overactivation of both T cells and microglia and propose avenues to study the pathogenesis of MS.

Th17 lymphocytes drive vascular and neuronal deficits in a mouse model of postinfectious autoimmune encephalitis.

Antibodies against neuronal receptors and synaptic proteins are associated with a group of ill-defined central nervous system (CNS) autoimmune diseases termed autoimmune encephalitides (AE), which are characterized by abrupt onset of seizures and/or movement and psychiatric symptoms. Basal ganglia encephalitis (BGE), representing a subset of AE syndromes, is triggered in children by repeated group A Streptococcus (GAS) infections that lead to neuropsychiatric symptoms. We have previously shown that multiple GAS infections of mice induce migration of Th17 lymphocytes from the nose into the brain, causing blood-brain barrier (BBB) breakdown, extravasation of autoantibodies into the CNS, and loss of excitatory synapses within the olfactory bulb (OB). Whether these pathologies induce functional olfactory deficits, and the mechanistic role of Th17 lymphocytes, is unknown. Here, we demonstrate that, whereas loss of excitatory synapses in the OB is transient after multiple GAS infections, functional deficits in odor processing persist. Moreover, mice lacking Th17 lymphocytes have reduced BBB leakage, microglial activation, and antibody infiltration into the CNS, and have their olfactory function partially restored. Th17 lymphocytes are therefore critical for selective CNS entry of autoantibodies, microglial activation, and neural circuit impairment during postinfectious BGE.

NLRX1 inhibits the early stages of CNS inflammation and prevents the onset of spontaneous autoimmunity.

Nucleotide-binding, leucine-rich repeat containing X1 (NLRX1) is a mitochondria-located innate immune sensor that inhibits major pro-inflammatory pathways such as type I interferon and nuclear factor-κB signaling. We generated a novel, spontaneous, and rapidly progressing mouse model of multiple sclerosis (MS) by crossing myelin-specific T-cell receptor (TCR) transgenic mice with Nlrx1-/- mice. About half of the resulting progeny developed spontaneous experimental autoimmune encephalomyelitis (spEAE), which was associated with severe demyelination and inflammation in the central nervous system (CNS). Using lymphocyte-deficient mice and a series of adoptive transfer experiments, we demonstrate that genetic susceptibility to EAE lies within the innate immune compartment. We show that NLRX1 inhibits the subclinical stages of microglial activation and prevents the generation of neurotoxic astrocytes that induce neuronal and oligodendrocyte death in vitro. Moreover, we discovered several mutations within NLRX1 that run in MS-affected families. In summary, our findings highlight the importance of NLRX1 in controlling the early stages of CNS inflammation and preventing the onset of spontaneous autoimmunity.

Selective Depletion of Antigen-Specific Antibodies for the Treatment of Demyelinating Disease.

Current treatments for antibody-mediated autoimmunity are associated with lack of specificity, leading to immunosuppressive effects. To overcome this limitation, we have developed a class of antibody-based therapeutics for the treatment of autoimmunity involving antibodies that recognize the autoantigen, myelin oligodendrocyte glycoprotein (MOG). These agents ("Seldegs," for selective degradation) selectively eliminate antigen (MOG)-specific antibodies without affecting the levels of antibodies of other specificities. Seldeg treatment of mice during antibody-mediated exacerbation of experimental autoimmune encephalomyelitis by patient-derived MOG-specific antibodies results in disease amelioration. Consistent with their therapeutic effects, Seldegs deliver their targeted antibodies to Kupffer and liver sinusoidal endothelial cells that are known to have tolerogenic effects. Our results show that Seldegs can ameliorate disease mediated by MOG-specific antibodies and indicate that this approach also has the potential to treat other autoimmune diseases where the specific clearance of antibodies is required.

The association between EAE development in mice and the production of autoantibodies and abzymes after immunization of mice with different antigens.

We have previously shown that immunization of C57BL/6 mice, prone to spontaneous development of experimental autoimmune encephalomyelitis (EAE), with three antigens (MOG35-55 , DNA-histone complex or DNA-methylated BSA complex), alters the differentiation profiles of bone marrow haematopoietic stem cells (HSCs). These are associated with the production of autoantibodies (auto-Abs) against these antigens and the formation of abzymes hydrolysing DNA, MOG, myelin basic protein (MBP) and histones. Immunization of mice with antigens accelerates the development of EAE. This work is the first to analyse the ratio of auto-Abs without and with catalytic activities at different stages of EAE development (onset, acute and remission phases) after immunization of mice with the three specific antigens. Prior to immunization and during spontaneous in-time development of EAE, the concentration of auto-Abs against MBP, MOG, histones and DNA and activities of IgG antibodies in the hydrolysis of substrates increased in parallel; correlation coefficients = +0.69-0.94. After immunization with MOG, DNA-histone complex or DNA-met-BSA complex, both positive (from +0.13 to +0.98) and negative correlations (from -0.09 to -0.69) were found between these values. Our study is the first showing that depending on the antigen, the relative amount of harmful auto-Abs without and abzymes with low or high catalytic activities may be produced only at onset and in acute or remission phases of EAE. The antigen governs the EAE development rate, whereby the ratio of auto-Abs without catalytic activity and with enzymatic activities of harmful abzymes hydrolysing MBP, MOG, histones and DNA varies strongly between different disease phases.

Recombinant myelin oligodendrocyte glycoprotein quality modifies evolution of experimental autoimmune encephalitis in macaques.

Experimental autoimmune encephalitis (EAE) is a well-recognized model for the study of human acquired demyelinating diseases (ADD), a group of inflammatory disorders of the central nervous system (CNS) characterized by inflammation, myelin loss, and neurological impairment of variable severity. In rodents, EAE is typically induced by active immunization with a combination of myelin-derived antigen and a strong adjuvant as complete Freund's adjuvant (CFA), containing components of the mycobacterial wall, while myelin antigen alone or associated with other bacterial components, as lipopolysaccharides (LPS), often fails to induce EAE. In contrast to this, EAE can be efficiently induced in non-human primates by immunization with the recombinant human myelin oligodendrocyte glycoprotein (rhMOG), produced in Escherichia coli (E. coli), purified and formulated with incomplete Freund's adjuvant (IFA), which lacks bacterial elements. Here, we provide evidence indicating how trace amounts of bacterial contaminants within rhMOG may influence the course and severity of EAE in the cynomolgus macaque immunized with rhMOG/IFA. The residual amount of E. coli contaminants, as detected with mass spectrometry within rhMOG protein stocks, were found to significantly modulate the severity of clinical, radiological, and histologic hallmarks of EAE in macaques. Indeed, animals receiving the purest rhMOG showed milder disease severity, increased numbers of remissions, and reduced brain damage. Histologically, these animals presented a wider diversity of lesion types, including changes in normal-appearing white matter and prephagocytic lesions. Non-human primates EAE model with milder histologic lesions reflect more accurately ADD and permits to study of the pathogenesis of disease initiation and progression.

STEAP4 expression in CNS resident cells promotes Th17 cell-induced autoimmune encephalomyelitis.

BACKGROUND: Multiple sclerosis (MS) is a debilitating neurological disease caused by autoimmune destruction of the myelin sheath. Experimental autoimmune encephalomyelitis (EAE) is a widely used animal model for the pathogenesis of MS. We and others have previously demonstrated that IL-17 is critical for the pathogenesis of EAE. The concentration of IL-17 is significantly higher in the sera of MS patients than in healthy controls and correlates with disease activity. Moreover, anti-IL-17 neutralizing antibody demonstrated promising efficacy in a phase II trial in MS patients, further substantiating a key pathogenic role for IL-17 in MS. While Th17 and IL-17 are emerging as a bona fide drivers for neuroinflammation, it remains unclear what effector molecule executes the inflammatory tissue destruction in Th17-driven EAE. METHODS: By microarray analysis, we found STEAP4 is a downstream molecule of IL-17 signaling in EAE. We then used STEAP4 global knockout mice and STEAP4 conditional knockout mice to test its role in the pathogenesis of EAE. RESULTS: Here, we report that the metalloreductase, STEAP4, is a key effector molecule that participates and contributes to the pathogenesis of Th17-mediated neuroinflammation in experimental autoimmune encephalomyelitis. STEAP4 knockout mice displayed delayed onset and reduced severity of EAE induced by active immunization. The reduced disease phenotype was not due to any impact of STEAP4 deficiency on myelin reactive T cells. In contrast, STEAP4 knockout mice were resistant to passively induced EAE, pointing to a role for STEAP4 in the effector stage of EAE. Notably, STEAP4 was only induced the spinal cord of EAE mice that received Th17 cells but not Th1 cells. Consistently, STEAP4 deficiency protected from only Th17 but not Th1-induced EAE. Finally, using Nestin-Cre STEAP4fl/fl mice, we showed that ablation of STEAP4 expression in the resident cells in the central nervous system attenuated disease severity in both active immunization and passive Th17 transfer-induced EAE. CONCLUSION: In this study, we identified STEAP4 as a Th17-specific effector molecule that participates and contributes to the pathogenesis of neuroinflammation, thus potentially provide a novel target for MS therapy.

Tolerogenic signals delivered by dendritic cells to T cells through a galectin-1-driven immunoregulatory circuit involving interleukin 27 and interleukin 10.

Despite their central function in orchestrating immunity, dendritic cells (DCs) can respond to inhibitory signals by becoming tolerogenic. Here we show that galectin-1, an endogenous glycan-binding protein, can endow DCs with tolerogenic potential. After exposure to galectin-1, DCs acquired an interleukin 27 (IL-27)-dependent regulatory function, promoted IL-10-mediated T cell tolerance and suppressed autoimmune neuroinflammation. Consistent with its regulatory function, galectin-1 had its highest expression on DCs exposed to tolerogenic stimuli and was most abundant from the peak through the resolution of autoimmune pathology. DCs lacking galectin-1 had greater immunogenic potential and an impaired ability to halt inflammatory disease. Our findings identify a tolerogenic circuit linking galectin-1 signaling, IL-27-producing DCs and IL-10-secreting T cells, which has broad therapeutic implications in immunopathology.

Cellular and molecular regulation of the programmed death-1/programmed death ligand system and its role in multiple sclerosis and other autoimmune diseases.

Programmed Cell Death 1 (PD-1) receptor and its ligands (PD-Ls) are essential to maintain peripheral immune tolerance and to avoid tissue damage. Consequently, altered gene or protein expression of this system of co-inhibitory molecules has been involved in the development of cancer and autoimmunity. Substantial progress has been achieved in the study of the PD-1/PD-Ls system in terms of regulatory mechanisms and therapy. However, the role of the PD-1/PD-Ls pathway in neuroinflammation has been less explored despite being a potential target of treatment for neurodegenerative diseases. Multiple Sclerosis (MS) is the most prevalent, chronic, inflammatory, and autoimmune disease of the central nervous system that leads to demyelination and axonal damage in young adults. Recent studies have highlighted the key role of the PD-1/PD-Ls pathway in inducing a neuroprotective response and restraining T cell activation and neurodegeneration in MS. In this review, we outline the molecular and cellular mechanisms regulating gene expression, protein synthesis and traffic of PD-1/PD-Ls as well as relevant processes that control PD-1/PD-Ls engagement in the immunological synapse between antigen-presenting cells and T cells. Also, we highlight the most recent findings regarding the role of the PD-1/PD-Ls pathway in MS and its murine model, experimental autoimmune encephalomyelitis (EAE), including the contribution of PD-1 expressing follicular helper T (TFH) cells in the pathogenesis of these diseases. In addition, we compare and contrast results found in MS and EAE with evidence reported in other autoimmune diseases and their experimental models, and review PD-1/PD-Ls-targeting therapeutic approaches.

Histone deacetylase 1 controls CD4+ T cell trafficking in autoinflammatory diseases.

CD4+ T cell trafficking is a fundamental property of adaptive immunity. In this study, we uncover a novel role for histone deacetylase 1 (HDAC1) in controlling effector CD4+ T cell migration, thereby providing mechanistic insight into why a T cell-specific deletion of HDAC1 protects against experimental autoimmune encephalomyelitis (EAE). HDAC1-deficient CD4+ T cells downregulated genes associated with leukocyte extravasation. In vitro, HDAC1-deficient CD4+ T cells displayed aberrant morphology and migration on surfaces coated with integrin LFA-1 ligand ICAM-1 and showed an impaired ability to arrest on and to migrate across a monolayer of primary mouse brain microvascular endothelial cells under physiological flow. Moreover, HDAC1 deficiency reduced homing of CD4+ T cells into the intestinal epithelium and lamina propria preventing weight-loss, crypt damage and intestinal inflammation in adoptive CD4+ T cell transfer colitis. This correlated with reduced expression levels of LFA-1 integrin chains CD11a and CD18 as well as of selectin ligands CD43, CD44 and CD162 on transferred circulating HDAC1-deficient CD4+ T cells. Our data reveal that HDAC1 controls T cell-mediated autoimmunity via the regulation of CD4+ T cell trafficking into the CNS and intestinal tissues.

Blockade of Kv1.3 potassium channel inhibits CD8+ T cell-mediated neuroinflammation via PD-1/Blimp-1 signaling.

Kv1.3 potassium channel is considered as a target for the treatment of autoimmune diseases such as multiple sclerosis (MS), since Kv1.3 blockade suppresses memory T cell activation including cytotoxic CD8+ T cells. However, the underlying signaling pathway related to autoimmune CD8+ T cell inhibition by Kv1.3 channel in neuroinflammatory diseases remains unclear. We found that ImK, a selective Kv1.3 blocker, reduced auto-reactive CD8+ T cell infiltration in the spinal cords of experimental autoimmune encephalomyelitis (EAE) rats, an animal model of MS. ImK suppressed transcriptional factor Blimp-1 expression and reduced the cytotoxicity of CD8+ T cells on neuronal cells. Furthermore, ImK upregulated co-inhibitory molecule PD-1 to inhibit B lymphocyte-induced maturation protein (Blimp-1) in an IL-2 independent way. In addition, PD-1 inhibitor impaired the suppression of ImK on CD8+ T cells and accelerated EAE progression. Our study demonstrated a novel regulatory mechanism of Kv1.3 blockade on modulating CD8+ T cell differentiation through PD-1/Blimp-1 signaling. This work expands the understanding of Kv1.3 channel for modulating neuroinflammation.

Interleukin-27 priming of T cells controls IL-17 production in trans via induction of the ligand PD-L1.

Interleukin-27 (IL-27) is a key immunosuppressive cytokine that counters T helper 17 (Th17) cell-mediated pathology. To identify mechanisms by which IL-27 might exert its immunosuppressive effect, we analyzed genes in T cells rapidly induced by IL-27. We found that IL-27 priming of naive T cells upregulated expression of programmed death ligand 1 (PD-L1) in a signal transducer and activator of transcription 1 (STAT1)-dependent manner. When cocultured with naive CD4(+) T cells, IL-27-primed T cells inhibited the differentiation of Th17 cells in trans through a PD-1-PD-L1 interaction. In vivo, coadministration of naive TCR transgenic T cells (2D2 T cells) with IL-27-primed T cells expressing PD-L1 inhibited the development of Th17 cells and protected from severe autoimmune encephalomyelitis. Thus, these data identify a suppressive activity of IL-27, by which CD4(+) T cells can restrict differentiation of Th17 cells in trans.

IL-11 Induces Encephalitogenic Th17 Cells in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis.

IL-11+CD4+ cells accumulate in the cerebrospinal fluid of patients with early relapsing-remitting multiple sclerosis (MS) and in active brain MS lesions. Mouse studies have confirmed a causal role of IL-11 in the exacerbation of relapsing-remitting experimental autoimmune encephalomyelitis (RREAE). Administration of IL-11 at the time of clinical onset of RREAE induced an acute exacerbation and increased clinical scores, which persisted during the entire course of the disease. IL-11 increased the numbers of spinal cord inflammatory foci, as well as the numbers of peripheral and CNS-infiltrating IL-17+CD4+ cells and IL-17A serum levels. Ag recall assays revealed that IL-11 induces IL-17A+, GM-CSF+, and IL-21+CD4+ myelin Ag-reactive cells. Passive transfer of these encephalitogenic CD4+ T cells induced severe RREAE with IL-17A+CCR6+ CD4+ and B cell accumulation within the CNS. Furthermore, passive transfer of nonmanipulated CNS-derived mononuclear cells from mice with RREAE after a single dose of IL-11 induced severe RREAE with increased accumulation of IL-17A+ and CCR6+ CD4+ cells within the CNS. These results suggest that IL-11 might serve as a biomarker of early autoimmune response and a selective therapeutic target for patients with early relapsing-remitting MS.

Follicular Helper CD4+ T Cells, Follicular Regulatory CD4+ T Cells, and Inducible Costimulator and Their Roles in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis.

Follicular helper CD4+ T (TFH) cells are a specialized subset of effector T cells that play a central role in orchestrating adaptive immunity. TFH cells mainly promote germinal center (GC) formation, provide help to B cells for immunoglobulin affinity maturation and class-switch recombination of B cells, and facilitate production of long-lived plasma cells and memory B cells. TFH cells express the nuclear transcriptional repressor B cell lymphoma 6 (Bcl-6), the chemokine (C-X-C motif) receptor 5 (CXCR5), the CD28 family members programmed cell death protein-1 (PD-1) and inducible costimulator (ICOS) and are also responsible for the secretion of interleukin-21 (IL-21) and IL-4. Follicular regulatory CD4+ T (TFR) cells, as a regulatory counterpart of TFH cells, participate in the regulation of GC reactions. TFR cells not only express markers of TFH cells but also express markers of regulatory T (Treg) cells containing FOXP3, glucocorticoid-induced tumor necrosis factor receptor (GITR), cytotoxic T lymphocyte antigen 4 (CTLA-4), and IL-10, hence owing to the dual characteristic of TFH cells and Treg cells. ICOS, expressed on activated CD4+ effector T cells, participates in T cell activation, differentiation, and effector process. The expression of ICOS is highest on TFH and TFR cells, indicating it as a key regulator of humoral immunity. Multiple sclerosis (MS) is a severe autoimmune disease that affects the central nervous system and results in disability, mediated by autoreactive T cells with evolving evidence of a remarkable contribution from humoral responses. This review summarizes recent advances regarding TFH cells, TFR cells, and ICOS, as well as their functional characteristics in relation to MS.

Male-specific IL-33 expression regulates sex-dimorphic EAE susceptibility.

The cellular and molecular basis of sex-dimorphic autoimmune diseases, such as the CNS demyelinating disease multiple sclerosis (MS), remains unclear. Our studies in the SJL mouse model of MS, experimental autoimmune encephalomyelitis (EAE), reveal that sex-determined differences in Il33 expression by innate immune cells in response to myelin peptide immunization regulate EAE susceptibility. IL-33 is selectively induced in PLP139-151-immunized males and activates type 2 innate lymphoid cells (ILC2s), cells that promote and sustain a nonpathogenic Th2 myelin-specific response. Without this attenuating IL-33 response, females generate an encephalitogenic Th17-dominant response, which can be reversed by IL-33 treatment. Mast cells are one source of IL-33 and we provide evidence that testosterone directly induces Il33 gene expression and also exerts effects on the potential for Il33 gene expression during mast cell development. Thus, in contrast to their pathogenic role in allergy, we propose a sex-specific role for both mast cells and ILC2s as attenuators of the pathogenic Th response in CNS inflammatory disease.

IL-1ß enables CNS access to CCR2hi monocytes and the generation of pathogenic cells through GM-CSF released by CNS endothelial cells.

Molecular interventions that limit pathogenic CNS inflammation are used to treat autoimmune conditions such as multiple sclerosis (MS). Remarkably, IL-1ß-knockout mice are highly resistant to experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Here, we show that interfering with the IL-1ß/IL-1R1 axis severely impairs the transmigration of myeloid cells across central nervous system (CNS) endothelial cells (ECs). Notably, we report that IL-1ß expression by inflammatory CCR2hi monocytes favors their entry into the spinal cord before EAE onset. Following activation with IL-1ß, CNS ECs release GM-CSF, which in turn converts monocytes into antigen-presenting cells (APCs). Accordingly, spinal cord-infiltrated monocyte-derived APCs are associated with dividing CD4+ T cells. Factors released from the interaction between IL-1ß-competent myeloid cells and CD4+ T cells are highly toxic to neurons. Together, our results suggest that IL-1ß signaling is an entry point for targeting both the initiation and exacerbation of neuroinflammation.