The critical role of IL-12 and the IL-12R beta 2 subunit in the generation of pathogenic autoreactive Th1 cells

Low Interleukin-12 Levels concerning Severe Malaria: A Systematic Review and Meta-Analysis

Although many studies have investigated the role of interleukin (IL)-12 cytokine in the pathogenesis of severe malaria, these studies were based on a limited number of participants, possibly affecting their outcomes. We analyzed the difference in IL-12 levels between patients with severe and uncomplicated malaria through a meta-analysis. A systematic review was conducted following the Cochrane Handbook for Systematic Reviews of Interventions and was reported according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement. Systematic literature searches were performed between 20 February and 2 March, 2022 in PubMed, Scopus, and Embase to identify studies reporting IL-12 levels in patients with severe and uncomplicated malaria. The quality of included studies was determined using the Strengthening the Reporting of Observational Studies in Epidemiology guidelines. The pooled mean difference (MD) in IL-12 between patients with severe and uncomplicated malaria was estimated using the DerSimonian-Laird method for the random-effects model. Altogether, 1885 potentially relevant articles were identified, and 10 studies enrolling 654 patients with severe malaria and 626 patients with uncomplicated malaria were included in the meta-analysis. Patients with severe malaria had lower mean IL-12 levels than those with uncomplicated malaria (p = 0.01, MD: -33.62, 95% confidence interval [CI]: -58.79 to -8.45, I2: 99.29%, 10 studies). In conclusion, decreased IL-12 levels might significantly contribute to the development of severe malaria. As most published literature demonstrated the role of IL-12 in animal models, human studies are required to understand the mechanisms involved in low IL-12 levels in patients with severe malaria.

Role of Genetic Polymorphisms in IL12Rβ2 in Chronic Obstructive Pulmonary Disease

Background

Chronic obstructive pulmonary disease (COPD) is the most common chronic inflammatory airway disease. Il-12r beta 2 (IL-12Rβ2) is important for the production of pathogenic Th1 cells. We aimed to explore the association between IL-12Rβ2 genetic variants and COPD risk among southern Chinese Han population.

Methods

We recruited 996 participants to perform an association analysis through SNPStats online software. We used false-positive report probability analysis to detect whether the positive findings were noteworthy. Haploview 4.2 software and SNPStats were used to conduct the haplotype analysis and linkage disequilibrium. Finally, the interaction of SNP-SNP in COPD risk was evaluated by multi-factor dimensionality reduction.

Results

The study found evidence that genetic loci in IL-12Rβ2 (rs2201584, rs1874791, rs6679356, and rs3790567) were potentially associated with the COPD susceptibility. In particular, IL-12Rβ2-rs2201584 and -rs1874791 showed close associations with COPD risk in both overall and several stratified analyses. Overall analysis or several stratified analyses indicated that allele A or homozygous genotype AA of IL-12Rβ2-rs2201584 were risk factors for COPD (Allele A: OR (95% CI) = 1.23 (1.02–1.48), p = 0.033; genotype AA: OR (95% CI) = 1.76 (1.15–2.69), p = 0.009). The allele A or homozygous genotype AA of IL-12Rβ2- rs1874791 were also risk factors for COPD (Allele A: OR (95% CI) = 1.36 (1.10–1.68), p = 0.004; genotype AA: OR (95% CI) = 2.17 (1.18–3.99), p = 0.013).

Conclusion

Intronic variants in IL-12Rβ2 (rs2201584, rs1874791, rs6679356, and rs3790567) were associated with the COPD susceptibility. In particular, there were sufficient evidences that IL-12Rβ2-rs2201584 and -rs1874791 were associated with the increasing risk of COPD.

Altered Plasma Metabolic Profiles in Chinese Patients With Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease that leads to the demyelination of nerve axons. An increasing number of studies suggest that patients with MS exhibit altered metabolic profiles, which might contribute to the course of MS. However, the alteration of metabolic profiles in Chinese patients with MS and their potential roles in regulating the immune system remain elusive. In this study, we performed a global untargeted metabolomics approach in plasma samples from 22 MS-affected Chinese patients and 21 healthy subjects. A total of 42 differentially abundant metabolites (DAMs) belonging to amino acids, lipids, and carbohydrates were identified in the plasma of MS patients and compared with those in healthy controls. We observed an evident reduction in the levels of amino acids, such as L-tyrosine, L-isoleucine, and L-tryptophan, whereas there was a great increase in the levels of L-glutamic acid and L-valine in MS-affected patients. The levels of lipid and carbohydrate metabolites, such as sphingosine 1-phosphate and myo-inositol, were also reduced in patients with MS. In addition, the concentrations of proinflammatory cytokines, such as IL-17 and TNF-α, were significantly increased, whereas those of several anti-inflammatory cytokines and chemokines, such as IL-1ra, IL-7, and MIP-1α, were distinctly reduced in the plasma of MS patients compared with those in healthy subjects. Interestingly, some DAMs, such as L-tryptophan and sphingosine 1-phosphate, showed an evident negative correlation with changes in the level of TNF-α and IL-17, while tightly positively correlating with altered concentrations of anti-inflammatory cytokines and chemokines, such as MIP-1α and RANTES. Our results revealed that altered metabolomic profiles might contribute to the pathogenesis and course of MS disease by modulating immuno-inflammatory responses in the peripheral system, which is essential for eliciting autoimmune responses in the central nervous system, thus resulting in the progression of MS. This study provides potential clues for developing therapeutic strategies for MS in the near future.

Inhibition of NADPH oxidase activation reduces EAE-induced white matter damage in mice

Background

To evaluate the role of NADPH oxidase-mediated reactive oxygen species (ROS) production in multiple sclerosis pathogenesis, we examined the effects of apocynin, an NADPH oxidase assembly inhibitor, on experimental autoimmune encephalomyelitis (EAE).

Methods

EAE was induced by immunization with myelin oligodendrocyte glycoprotein (MOG (35-55)) in C57BL/6 female mice. Three weeks after initial immunization, the mice were analyzed for demyelination, immune cell infiltration, and ROS production. Apocynin (30 mg/kg) was given orally once daily for the entire experimental course or after the typical onset of clinical symptom (15 days after first MOG injection).

Results

Clinical signs of EAE first appeared on day 11 and reached a peak level on day 19 after the initial immunization. The daily clinical symptoms of EAE mice were profoundly reduced by apocynin. The apocynin-mediated inhibition of the clinical course of EAE was accompanied by suppression of demyelination, reduced infiltration by encephalitogenic immune cells including CD4, CD8, CD20, and F4/80-positive cells. Apocynin reduced MOG-induced pro-inflammatory cytokines in cultured microglia. Apocynin also remarkably inhibited EAE-associated ROS production and blood–brain barrier (BBB) disruption. Furthermore, the present study found that post-treatment with apocynin also reduced the clinical course of EAE and spinal cord demyelination.

Conclusions

These results demonstrate that apocynin inhibits the clinical features and neuropathological changes associated with EAE. Therefore, the present study suggests that inhibition of NADPH oxidase activation by apocynin may have a high therapeutic potential for treatment of multiple sclerosis pathogenesis.

A mushroom extract Piwep from Phellinus igniarius ameliorates experimental autoimmune encephalomyelitis by inhibiting immune cell infiltration in the spinal cord

The present study aimed to evaluate the therapeutic potential of a mushroom extract from Phellinus igniarius in an animal model of multiple sclerosis. The medicinal mushroom, Phellinus igniarius, contains biologically active compounds that modulate the human immune system. Experimental autoimmune encephalomyelitis (EAE) was induced by immunization with myelin oligodendrocyte glycoprotein (MOG 35-55) in C57BL/6 female mice. A water-ethanol extract of Phellinus igniarius (Piwep) was delivered intraperitoneally every other day for the entire experimental course. Three weeks after the initial immunization, demyelination and immune cell infiltration in the spinal cord were examined. Piwep injection profoundly decreased the daily incidence rate and clinical score of EAE. The Piwep-mediated inhibition of the clinical course of EAE was accompanied by suppression of demyelination and infiltration of encephalitogenic immune cells including CD4+ T cells, CD8+ T cells, macrophages, and B cells in the spinal cord. Piwep reduced expression of vascular cell adhesion molecule-1 (VCAM-1) in the spinal cord and integrin-α 4 in the lymph node of EAE mice. Piwep also inhibited proliferation of lymphocytes and secretion of interferon-γ in the lymph node of EAE mice. The results suggest that a mushroom extract, Piwep, may have a high therapeutic potential for ameliorating multiple sclerosis progression.

Role of Th17 cells in the pathogenesis of CNS inflammatory demyelination

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). The etiology of MS is not well understood, but it is believed that myelin-specific CD4(+) T cells play a central role in initiating and orchestrating CNS inflammation. In this scenario, CD4(+) T cells, activated in the periphery, infiltrate the CNS, where, by secreting cytokines and chemokines, they start an inflammatory cascade. Given the central role of CD4(+) T cells in CNS autoimmunity, they have been studied extensively, principally by using experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the late 1980s, CD4(+) T cells, based on their cytokine production, were divided into two helper lineages, Th1 and Th2 cells. It was postulated that Th1 cells, which produce IFN-γ, mediate inflammation of the CNS in MS/EAE, while Th2 cells, which produce IL-4, have a beneficial effect in disease, because of their antagonistic effect on Th1 cells. The Th1/Th2 paradigm remained the prevailing view of MS/EAE pathogenesis until 2005, when a new lineage, Th17, was discovered. In a relatively short period of time it became apparent that Th17 cells, named after their hallmark cytokine, IL-17A, play a crucial role in many inflammatory diseases, including EAE, and likely in MS as well. The Th17 paradigm developed rapidly, initiating the debate of whether Th1 cells contribute to EAE/MS pathogenesis at all, or if they might even have a protective role due to their antagonistic effects on Th17 cells. Numerous findings support the view that Th17 cells play an essential role in autoimmune CNS inflammation, perhaps mainly in the initial phases of disease. Th1 cells likely contribute to pathogenesis, with their role possibly more pronounced later in disease. Hence, the current view on the role of Th cells in MS/EAE pathogenesis can be called the Th17/Th1 paradigm. It is certain that Th17 cells will continue to be the focus of intense investigation aimed at elucidating the pathogenesis of CNS autoimmunity.

CNS-specific therapy for ongoing EAE by silencing IL-17 pathway in astrocytes

The interleukin-17 (IL-17) cytokine family is crucial to the progression of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). It has been shown in a neuroectoderm-specific knockout study that astrocyte-restricted ablation of Act1, a key and common transcription factor for signals mediated by IL-17 family members (IL-17A, IL-17F, and IL-17C), ameliorates EAE. However, the effect of Act1 deficiency in astrocytes on ongoing disease, which is of clinical relevance for MS therapy, has not been investigated. Here we report that intracerebroventricular (i.c.v.) injection of a novel lentiviral vector (shAct1) to knockdown Act1 expression in astrocytes effectively inhibited disease progression at EAE induction, clinical onset, and peak of disease (ongoing phases), with significantly reduced numbers of infiltrating inflammatory cells and percentage of Th17 cells in the central nervous system (CNS). This was mainly due to the suppressed expression of Th17-related chemokines in astrocytes, while neurotrophic factors in the CNS and immune responses in the periphery were not affected. These results demonstrate that blocking the IL-17 pathways in astrocytes is a promising therapeutic approach for MS in a CNS-specific manner, which does not interfere with systemic immune responses, a major concern in conventional MS therapy.

A GWAS follow-up study reveals the association of the IL12RB2 gene with systemic sclerosis in Caucasian populations

A single-nucleotide polymorphism (SNP) at the IL12RB2 locus showed a suggestive association signal in a previously published genome-wide association study (GWAS) in systemic sclerosis (SSc). Aiming to reveal the possible implication of the IL12RB2 gene in SSc, we conducted a follow-up study of this locus in different Caucasian cohorts. We analyzed 10 GWAS-genotyped SNPs in the IL12RB2 region (2309 SSc patients and 5161 controls). We then selected three SNPs (rs3790567, rs3790566 and rs924080) based on their significance level in the GWAS, for follow-up in an independent European cohort comprising 3344 SSc and 3848 controls. The most-associated SNP (rs3790567) was further tested in an independent cohort comprising 597 SSc patients and 1139 controls from the USA. After conditional logistic regression analysis of the GWAS data, we selected rs3790567 [P(MH)= 1.92 × 10(-5) odds ratio (OR) = 1.19] as the genetic variant with the firmest independent association observed in the analyzed GWAS peak of association. After the first follow-up phase, only the association of rs3790567 was consistent (P(MH)= 4.84 × 10(-3) OR = 1.12). The second follow-up phase confirmed this finding (P(χ2) = 2.82 × 10(-4) OR = 1.34). After performing overall pooled-analysis of all the cohorts included in the present study, the association found for the rs3790567 SNP in the IL12RB2 gene region reached GWAS-level significant association (P(MH)= 2.82 × 10(-9) OR = 1.17). Our data clearly support the IL12RB2 genetic association with SSc, and suggest a relevant role of the interleukin 12 signaling pathway in SSc pathogenesis.

PPAR Regulation of Inflammatory Signaling in CNS Diseases

Central nervous system (CNS) is an immune privileged site, nevertheless inflammation associates with many CNS diseases. Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that regulate immune and inflammatory responses. Specific ligands for PPARα, γ, and δ isoforms have proven effective in the animal models of multiple sclerosis (MS), Alzheimer's disease, Parkinson's disease, and trauma/stroke, suggesting their use in the treatment of neuroinflammatory diseases. The activation of NF-κB and Jak-Stat signaling pathways and secretion of inflammatory cytokines are critical in the pathogenesis of CNS diseases. Interestingly, PPAR agonists mitigate CNS disease by modulating inflammatory signaling network in immune cells. In this manuscript, we review the current knowledge on how PPARs regulate neuroinflammatory signaling networks in CNS diseases.

IDO upregulates regulatory T cells via tryptophan catabolite and suppresses encephalitogenic T cell responses in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a Th1 and Th17 cell-mediated autoimmune disease of the CNS. IDO and tryptophan metabolites have inhibitory effects on Th1 cells in EAE. For Th17 cells, IDO-mediated tryptophan deprivation and small molecule halofuginone-induced amino acid starvation response were shown to activate general control nonrepressed 2 (GCN2) kinase that directly or indirectly inhibits Th17 cell differentiation. However, it remains unclear whether IDO and tryptophan metabolites impact the Th17 cell response by mechanisms other than the GCN2 kinase pathway. In this article, we show that IDO-deficient mice develop exacerbated EAE with enhanced encephalitogenic Th1 and Th17 cell responses and reduced regulatory T cell (Treg) responses. Administration of the downstream tryptophan metabolite 3-hydroxyanthranillic acid (3-HAA) enhanced the percentage of Tregs, inhibited Th1 and Th17 cells, and ameliorated EAE. We further demonstrate that Th17 cells are less sensitive to direct suppression by 3-HAA than are Th1 cells. 3-HAA treatment in vitro reduced IL-6 production by activated spleen cells and increased expression of TGF-β in dendritic cells (DCs), which correlated with enhanced levels of Tregs, suggesting that 3-HAA-induced Tregs contribute to inhibition of Th17 cells. By using a DC-T cell coculture, we found that 3-HAA-treated DCs expressed higher levels of TGF-β and had properties to induce generation of Tregs from anti-CD3/anti-CD28-stimulated naive CD4(+) T cells. Thus, our data support the hypothesis that IDO induces the generation of Tregs via tryptophan metabolites, such as 3-HAA, which enhances TGF-β expression from DCs and promotes Treg differentiation.

T helper 17 cells: discovery, function, and physiological trigger

In the few years since their discovery, T helper 17 cells (T(H)17) have been shown to play an important role in host defense against infections, and in tissue inflammation during autoimmunity. T(H)17 cells produce IL-17, IL-21, IL-10, and IL-22 cytokines, and thus have broad effects on a variety of tissues. Notably, the requirement for the immunosuppressive cytokine TGF-beta along with the pro-inflammatory cytokine IL-6 for T(H)17 differentiation supports the intimate relationship between the T(H)17 subset and FOXP3(+) regulatory T cells. Here, we discuss current knowledge on effector functions and differentiation of the T(H)17 lineage. Furthermore, we now know of a physiological stimulus for T(H)17 differentiation: innate immune recognition of cells undergoing apoptosis as a direct result of infection induces unique development of this subset. As our knowledge of T(H)17 and T regulatory cells grows, we are building on a new framework for the understanding of effector T cell differentiation and the biology of CD4(+) T cell adaptive immune responses.

Signal transducer and activation of transcription (STAT) 4beta, a shorter isoform of interleukin-12-induced STAT4, is preferentially activated by estrogen

Estrogen, a natural immunomodulatory compound, has been shown to promote the induction of a prototype T helper 1 cytokine, interferon (IFN)-gamma, as well as to up-regulate IFNgamma-mediated proinflammatory molecules (nitric oxide, cyclooxygenase 2, monocyte chemoattractant protein 1). Because IL-12 is a major IFNgamma-inducing cytokine, in this study we investigated whether estrogen treatment of wild-type C57BL/6 mice alters IL-12-mediated signaling pathways. A recent study has shown that IL-12 activates two isoforms of signal transducer and activation of transcription (STAT) 4, a normal-sized (full-length STAT4alpha) and a truncated form (STAT4beta). Interestingly, we found that estrogen treatment preferentially up-regulates the phosphorylation of STAT4beta in splenic lymphoid cells. Time kinetic data showed the differential activation of STAT4beta in splenic lymphoid cells from estrogen-treated mice, but not in cells from placebo controls. The activation of STAT4beta was mediated by IL-12 and not IFNgamma because deliberate addition or neutralization of IL-12, but not IFNgamma, affected the activation of STAT4beta. In contrast to IL-12-induced activation of STAT4beta in cells from estrogen-treated mice, STAT4alpha was not increased, rather it tended to be decreased. In this context, STAT4alpha-induced p27(kip1) protein was decreased in concanavalin A + IL-12-activated lymphocytes from estrogen-treated mice only. By using the in vitro DNA binding assay, we confirmed the ability of pSTAT4beta to bind to the IFNgamma-activated sites (IFNgamma activation sequences)/STAT4-binding sites in estrogen-treated mice. Our data are the first to show that estrogen apparently has selective effects on IL-12-mediated signaling by preferentially activating STAT4beta. These novel findings are likely to provide new knowledge with regard to estrogen regulation of inflammation.

Generation of a protective T-cell response following coronavirus infection of the central nervous system is not dependent on IL-12/23 signaling

The functional role of IL-12 and IL-23 in host defense and disease following viral infection of the CNS was determined. Instillation of mouse hepatitis virus (MHV, a positive-strand RNA virus) into the CNS of mice results in acute encephalitis followed by a chronic immune-mediated demyelinating disease. Antibody-mediated blocking of either IL-23 (anti-IL-23p19) or IL-12 and IL-23 (anti-IL-12/23p40) signaling did not mute T-cell trafficking into the CNS or antiviral effector responses and mice were able to control viral replication within the brain. Therapeutic administration of either anti-IL-23p19 or anti-IL-12/23p40 to mice with viral-induced demyelination did not attenuate T-cell or macrophage infiltration into the CNS nor improve clinical disease or diminish white matter damage. In contrast, treatment of mice with anti-IL-12/23p40 or anti-IL-23p19 resulted in inhibition of the autoimmune model of demyelination, experimental autoimmune encephalomyelitis (EAE). These data indicate that (1) IL-12 and IL-23 signaling are dispensable in generating a protective T-cell response following CNS infection with MHV, and (2) IL-12 and IL-23 do not contribute to demyelination in a model independent of autoimmune T-cell-mediated pathology. Therefore, therapeutic targeting of IL-12 and/or IL-23 for the treatment of autoimmune diseases may offer unique advantages by reducing disease severity without muting protective responses following viral infection.

Human leukocyte antigen and cytokine receptor gene polymorphisms associated with heterogeneous immune responses to mumps viral vaccine

OBJECTIVES

Mumps outbreaks continue to occur throughout the world, including in highly vaccinated populations. Vaccination against mumps has been successful; however, humoral and cellular immune responses to mumps vaccines vary significantly from person to person. We set out to assess whether HLA and cytokine gene polymorphisms are associated with variations in the immune response to mumps viral vaccine.

METHODS

To identify genetic factors that might contribute to variations in mumps vaccine-induced immune responses, we performed HLA genotyping in a group of 346 healthy schoolchildren (12-18 years of age) who previously received 2 doses of live mumps vaccine. Single-nucleotide polymorphisms (minor allele frequency of >5%) in cytokine and cytokine receptor genes were genotyped for a subset of 118 children.

RESULTS

Median values for mumps-specific antibody titers and lymphoproliferative stimulation indices were 729 IU/mL and 4.8, respectively. Girls demonstrated significantly higher mumps antibody titers than boys, indicating gender-linked genetic differences in humoral immune response. Significant associations were found between the HLA-DQB1*0303 alleles and lower mumps-specific antibody titers. An interesting finding was the association of several HLA class II alleles with mumps-specific lymphoproliferation. Alleles of the DRB1 (*0101, *0301, *0801, *1001, *1201, and *1302), DQA1 (*0101, *0105, *0401, and *0501), and DQB1 (*0201, *0402, and *0501) loci were associated with significant variations in lymphoproliferative immune responses to mumps vaccine. Additional associations were observed with single-nucleotide polymorphisms in the interleukin-10RA, interleukin-12RB1, and interleukin-12RB2 cytokine receptor genes. Minor alleles for 4 single-nucleotide polymorphisms within interleukin-10RA and interleukin-12RB genes were associated with variations in humoral and cellular immune responses to mumps vaccination.

CONCLUSIONS

These data suggest the important role of HLA and immunoregulatory cytokine receptor gene polymorphisms in explaining variations in mumps vaccine-induced immune responses.

IL-13-mediated gender difference in susceptibility to autoimmune encephalomyelitis

Females tend to have stronger Th1-mediated immune responses and are more prone to develop autoimmune diseases, including multiple sclerosis. Macrophages are major effector cells capable of mediating or modulating immune responses in experimental autoimmune encephalomyelitis (EAE). IL-13 and estrogen have opposing roles on macrophages (the former enhancing and the latter inhibiting) in terms of MHC class II (MHC II) up-regulation and, thus, these factors might influence susceptibility to EAE differently in females vs males. In accordance with this hypothesis, females lacking IL-13 displayed lower incidence and milder EAE disease severity than males after immunization with myelin oligodendrocyte glycoprotein (MOG)-35-55 peptide/CFA/pertussis toxin. Female IL-13 knockout (KO) mice with EAE consistently had reduced infiltration of CD11b(+) macrophages in the CNS along with significantly reduced expression of MHC II on these cells. Impaired MHC II expression was further corroborated upon LPS stimulation of female but not male bone marrow-derived CD11b(+) macrophages from IL-13KO mice, with restored expression after IL-13 pretreatment of female but not male macrophages. APCs from IL-13KO females induced less proliferation by MOG-35-55-reactive T cells, and splenocytes from MOG peptide-immunized females had lower expression of IL-12, IFN-gamma, MIP-2, and IFN-gamma-inducible protein 10 than males. In contrast, these splenocytes had higher expression of anti-inflammatory factors, IL-10, TGF-beta1, and FoxP3, a cytokine pattern typical of regulatory type II monocytes. These data suggest that the difference in EAE susceptibility in females is strongly influenced by gender-specific proinflammatory effects of IL-13, mediated in part through up-regulation of Th1-inducing cytokines and MHC II on CD11b(+) macrophages.

CB2 cannabinoid receptors as an emerging target for demyelinating diseases: from neuroimmune interactions to cell replacement strategies

Amongst the various demyelinating diseases that affect the central nervous system, those induced by an inflammatory response stand out because of their epidemiological relevance. The best known inflammatory-induced demyelinating disease is multiple sclerosis, but the immune response is a common pathogenic mechanism in many other less common pathologies (e.g., acute disseminated encephalomyelitis and acute necrotizing haemorrhagic encephalomyelitis). In all such cases, modulation of the immune response seems to be a logical therapeutic approach. Cannabinoids are well known immunomodulatory molecules that act through CB1 and CB2 receptors. While activation of CB1 receptors has a psychotropic effect, activation of CB2 receptors alone does not. Therefore, to bypass the ethical problems that could result from the treatment of inflammation with psychotropic molecules, considerable effort is being made to study the potential therapeutic value of activating CB2 receptors. In this review we examine the current knowledge and understanding of the utility of cannabinoids as therapeutic molecules for inflammatory-mediated demyelinating pathologies. Moreover, we discuss how CB2 receptor activation is related to the modulation of immunopathogenic states.

Cytokines: powerful regulators of glial cell activation

It is now clear that cytokines function as powerful regulators of glial cell function in the central nervous system (CNS), either inhibiting or promoting their contribution to CNS pathology. Although these interactions are complex, the availability of animals with targeted deletions of these genes and/or their receptors, as well as transgenic mice in which cytokine expression has been targeted to specific cell types, and the availability of purified populations of glia that can be studied in vitro, has provided a wealth of interesting and frequently surprising data relevant to this activity. A particular feature of many of these studies is that it is the nature of the receptor that is expressed, rather than the cytokine itself, that regulates the functional properties of these cytokines. Because cytokine receptors are themselves modulated by cytokines, it becomes evident that the effects of these cytokines may change dramatically depending upon the cytokine milieu present in the immediate environment. An additional exciting aspect of these studies is the previously underappreciated role of these factors in repair to the CNS. In this review, we focus on current information that has helped to define the role of cytokines in regulating glial cell function as it relates to the properties of microglia and astrocytes.

Production of interleukin-13 by human dendritic cells after stimulation with protein allergens is a key factor for induction of T helper 2 cytokines and is associated with activation of signal transducer and activator of transcription-6

Dendritic cells (DC) are able to induce not only T helper 1 (Th1) but also Th2 immune responses after stimulation with allergens. While DC-derived interleukin (IL)-12 and IL-18 are the key factors for the induction of Th1 cells, early signals being involved in Th2 differentiation are less well characterized so far. To analyse such early signals we used an antigen-specific setting with CD4+ T cells from atopic donors stimulated in the presence of autologous mature DC, which were pulsed with different allergen doses. The addition of increasing amounts of allergen during DC maturation with tumour necrosis factor-alpha, IL-1beta and prostaglandin E2 resulted in enhanced secretion of IL-6 and IL-12 by DC followed by increased production of Th1 (interferon-gamma; IFN-gamma) as well as Th2 (IL-4, IL-5) cytokines by CD4+ T cells. The coculture of allergen-treated DC and CD4+ T cells also led to a dose-dependent expression of active signal transducer and activator of transcription-6 (STAT6), which was visible already after 1 hr. Additionally, rapid phosphorylation of STAT6 was seen in immature DC after stimulation with allergens but not with lipopolysaccharide or human serum albumin. STAT6 phosphorylation was associated with the production of IL-13 by DC. The addition of neutralizing anti-IL-13 antibodies during maturation of DC inhibited STAT6 phosphorylation in CD4+ T cells as well as the production of IL-4, and to a lesser extent of IL-5, while IFN-gamma production was not affected. Addition of exogenous IL-13 enhanced mainly the secretion of IL-4. Taken together, DC-derived IL-13, which is released after exposure to allergens appears to be one of the critical factors for DC to acquire the capability to induce Th2 cytokine production.

Parasite-induced lipoxin A4 is an endogenous regulator of IL-12 production and immunopathology in Toxoplasma gondii infection

The production of interleukin (IL)-12 is critical for the development of interferon (IFN)-gamma-dependent resistance to Toxoplasma gondii. Nevertheless, when this response is dysregulated, such as occurs in the absence of IL-10, the uncontrolled inflammation that results can have lethal consequences for the host. Recently, we demonstrated that lipoxin (LX)A(4), an eicosanoid mediator that depends on 5-lipoxygenase (LO) for its biosynthesis, exerts a regulatory role on dendritic cell IL-12 production triggered artificially by a T. gondii extract. We now formally establish the physiological relevance of this pathway in the systemic control of IL-12 production induced by live T. gondii infection and demonstrate its function to be distinct from that of IL-10. Thus, T. gondii-exposed wild-type, but not 5-LO-deficient animals, produced high levels of serum LXA(4) beginning at the onset of chronic infection. Moreover, 5-LO(-/-), in contrast to wild-type mice, succumbed during the same period displaying a marked encephalitis. The increased mortality of the 5-LO(-/-) animals was also associated with significant elevations of IL-12 and IFN-gamma and was completely prevented by the administration of a stable LXA(4) analogue. Together, these findings demonstrate a new pathway involving the induction of host LXs for the in vivo regulation of proinflammatory responses during microbial infection.

Experimental autoimmune encephalitis and inflammation in the absence of interleukin-12

IL-12 is considered a critical proinflammatory cytokine for autoimmune diseases such as multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). IL-12 is a heterodimer composed of a p35 subunit and a common p40 subunit shared by other cytokines. Both IL-12 p40(-/-) and p35(-/-) mice fail to produce IL-12 p70 heterodimer. However, in contrast to p40(-/-) mice, p35(-/-) mice are highly susceptible to the induction of EAE, establishing that IL-12 p70 is not essential for the development of EAE. When compared with wild-type mice, both p40(-/-) and p35(-/-) mice show deficiencies in primary IFN-gamma responses by lymph node cells. Expression profiling of the inflamed CNS revealed that Th2 cytokines such as IL-4 and IL-10 are upregulated in p35(-/-) mice, whereas LT-alpha and TNF-alpha levels are reduced. These studies show that a molecule other than IL-12 p70, which uses the p40 subunit, fulfills the functions previously attributed to IL-12 with regard to the development and pathogenesis of this autoimmune disease.

Immune function of microglia

During the past decade, mechanisms involved in the immune surveillance of the central nervous system (CNS) have moved to the forefront of neuropathological research mainly because of the recognition that most neurological disorders involve activation and, possibly, dysregulation of microglia, the intrinsic macrophages of the CNS. Increasing evidence indicates that, in addition to their well-established phagocytic function, microglia may also participate in the regulation of non specific inflammation as well as adaptive immune responses. This article focuses on the signals regulating microglia innate immune functions, the role of microglia in antigen presentation, and their possible involvement in the development of CNS immunopathology.

Interleukin-18 regulates both Th1 and Th2 responses

Although interleukin-18 is structurally homologous to IL-1 and its receptor belongs to the IL-1R/Toll-like receptor (TLR) superfamily, its function is quite different from that of IL-1. IL-18 is produced not only by types of immune cells but also by non-immune cells. In collaboration with IL-12, IL-18 stimulates Th1-mediated immune responses, which play a critical role in the host defense against infection with intracellular microbes through the induction of IFN-gamma. However, the overproduction of IL-12 and IL-18 induces severe inflammatory disorders, suggesting that IL-18 is a potent proinflammatory cytokine that has pathophysiological roles in several inflammatory conditions. IL-18 mRNA is expressed in a wide range of cells including Kupffer cells, macrophages, T cells, B cells, dendritic cells, osteoblasts, keratinocytes, astrocytes, and microglia. Thus, the pathophysiological role of IL-18 has been extensively tested in the organs that contain these cells. Somewhat surprisingly, IL-18 alone can stimulate Th2 cytokine production as well as allergic inflammation. Therefore, the functions of IL-18 in vivo are very heterogeneous and complicated. In principle, IL-18 enhances the IL-12-driven Th1 immune responses, but it can also stimulate Th2 immune responses in the absence of IL-12.

Interferon beta1a treatment modulates TH1 expression in gammadelta + T cells from relapsing-remitting multiple sclerosis patients

A paradigm exists that multiple sclerosis is causally related to dysregulation of TH1 inflammatory cytokines and TH2 antiinflammatory cytokines. The cytokine source(s) that initiate the imbalances are unknown. In this study, gammadelta, CD4, and CD8 T cell receptor-positive (TCR+) cells were isolated from the blood of 26 definitive relapsing-remitting multiple sclerosis patients prior to interferon beta-1a (IFNbeta1a) therapy and following 8-10 weeks of this therapy. The bioactivities of interferon gamma (IFNgamma), interleukin 10 (IL10), and interleukin 12 (IL12) were determined. The concentrations of IFN-gamma, IL10, and IL12 from each cell type did not change significantly with IFNbeta1a treatment. The IL10 secreted by gammadelta TCR+ cells strongly correlated with the IL12 secreted by the same gammadelta TCR+ cells, supporting the paradigm. Furthermore, IFNbeta1a therapy decreased the gammadelta TCR+ cell secretion of TH1 cytokines after 8-10 weeks of therapy.