Obesity promotes prolonged ovalbumin‐induced airway inflammation modulating T helper type 1 (Th1), Th2 and Th17 immune responses in BALB/c mice

Clinical and epidemiological studies indicate that obesity affects the development and phenotype of asthma by inducing inflammatory mechanisms in addition to eosinophilic inflammation. The aim of this study was to assess the effect of obesity on allergic airway inflammation and T helper type 2 (Th2) immune responses using an experimental model of asthma in BALB/c mice. Mice fed a high‐fat diet (HFD) for 10 weeks were sensitized and challenged with ovalbumin (OVA), and analyses were performed at 24 and 48 h after the last OVA challenge. Obesity induced an increase of inducible nitric oxide synthase (iNOS)‐expressing macrophages and neutrophils which peaked at 48 h after the last OVA challenge, and was associated with higher levels of interleukin (IL)‐4, IL‐9, IL‐17A, leptin and interferon (IFN)‐γ in the lungs. Higher goblet cell hyperplasia was associated with elevated mast cell influx into the lungs and trachea in the obese allergic mice. In contrast, early eosinophil influx and lower levels of IL‐25, thymic stromal lymphopoietin (TSLP), CCL11 and OVA‐specific immunoglobulin (IgE) were observed in the obese allergic mice in comparison to non‐obese allergic mice. Moreover, obese mice showed higher numbers of mast cells regardless of OVA challenge. These results indicate that obesity affects allergic airway inflammation through mechanisms involving mast cell influx and the release of TSLP and IL‐25, which favoured a delayed immune response with an exacerbated Th1, Th2 and Th17 profile. In this scenario, an intense mixed inflammatory granulocyte influx, classically activated macrophage accumulation and intense mucus production may contribute to a refractory therapeutic response and exacerbate asthma severity.     

Interleukin‐23 promotes intestinal T helper type17 immunity and ameliorates obesity‐associated metabolic syndrome in a murine high‐fat diet model

We addressed the role of interleukin‐23 (IL‐23) in driving the intestinal T helper type 17 (Th17) response during obesity and metabolic syndrome progression induced by a high‐fat diet (HFD). Diet‐induced obese and lean mice received HFD or control diet (CTD), respectively, for 20 weeks. The nutritional, metabolic and immune parameters were examined at weeks 9 and 20. Gene and protein IL‐23p19 and IL‐23 receptor expression was increased in the ileum of obese wild‐type mice (WT) fed the HFD for 9 weeks. Mice lacking IL‐23 and fed the HFD exhibited greater weight gain, higher fat accumulation, adipocyte hypertrophy and hepatic steatosis. Notably, these mice had more glucose intolerance, insulin resistance and associated metabolic alterations, such as hyperinsulinaemia and hyperlipidaemia. IL‐23 deficiency also significantly reduced protein levels of IL‐17, CCL20 and neutrophil elastase in the ileum and reduced Th17 cell expansion in the mesenteric lymph nodes of the HFD mice. Of importance, IL‐23‐deficient mice exhibited increased gut permeability and blood bacterial translocation compared with WT mice fed HFD. Finally, metagenomics analysis of gut microbiota revealed a dramatic outgrowth of Bacteroidetes over Firmicutes phylum with the prevalence of Bacteroides genera in the faeces of IL‐23‐deficient mice after HFD. In summary, IL‐23 appears to maintain the Th17 response and neutrophil migration into the intestinal mucosa, minimizing the gut dysbiosis and protecting against obesity and metabolic disease development in mice.     

T‐bet is essential for Th1‐mediated,but not Th17‐mediated,CNS autoimmune disease

T cells that produce both IL‐17 and IFN‐γ, and co‐express ROR‐γt and T‐bet, are often found at sites of autoimmune inflammation. However, it is unknown whether this co‐expression of T‐bet with ROR‐γt is a prerequisite for immunopathology. We show here that T‐bet is not required for the development of Th17‐driven experimental autoimmune encephalomyelitis (EAE). The disease was not impaired in T‐bet^?/? mice and was associated with low IFN‐γ production and elevated IL‐17 production among central nervous system (CNS) infiltrating CD4⁺ T cells. T‐bet^?/? Th17 cells generated in the presence of IL‐6/TGF‐β/IL‐1 and IL‐23 produced GM‐CSF and high levels of IL‐17 and induced disease upon transfer to naïve mice. Unlike their WT counterparts, these T‐bet^?/– Th17 cells did not exhibit an IL‐17→IFN‐γ switch upon reencounter with antigen in the CNS, indicating that this functional change is not critical to disease development. In contrast, T‐bet was absolutely required for the pathogenicity of myelin‐responsive Th1 cells. T‐bet‐deficient Th1 cells failed to accumulate in the CNS upon transfer, despite being able to produce GM‐CSF. Therefore, T‐bet is essential for establishing Th1‐mediated inflammation but is not required to drive IL‐23‐induced GM‐CSF production, or Th17‐mediated autoimmune inflammation.     

The choice of adjuvant determines the cytokine profile of T cells in proteoglycan‐induced arthritis but does not influence disease severity

Rheumatoid arthritis (RA) is a debilitating autoimmune disease characterized by chronic inflammation of the synovial joints. Collagen‐induced arthritis (CIA) and proteoglycan‐induced arthritis (PGIA) are mouse models of inflammatory arthritis; CIA is a T helper type 17 (Th17) ‐dependent disease that is induced with antigen in complete Freund's adjuvant, whereas PGIA is Th1‐mediated and is induced using antigen in dimethyldioctadecyl‐ammonium bromide (DDA) as an adjuvant. To investigate whether the type of adjuvant determines the cytokine profile of the pathogenic T cells, we have compared the effect of CFA and DDA on T‐cell responses in a single arthritis model. No differences in incidence or disease severity between aggrecan‐T‐cell receptor transgenic mice immunized with aggrecan in either CFA or DDA were observed. Immunization with CFA resulted in a higher proportion of Th17 cells, whereas DDA induced more Th1 cells. However, the levels of interleukin‐17 (IL‐17) produced by T cells isolated from CFA‐immunized mice after antigen‐specific stimulation were not significantly different from those found in DDA‐immunized mice, indicating that the increased proportion of Th17 cells did not result in significantly higher ex vivo IL‐17 levels. Hence, the choice of adjuvant can affect the overall proportions of Th1 and Th17 cells, without necessarily affecting the level of cytokine production or disease incidence and severity.     

Both IFN‐γ and IL‐17 are required for the development of severe autoimmune gastritis

IL‐17, produced by a distinct lineage of CD4⁺ helper T (Th) cells termed Th17 cells, induces the production of pro‐inflammatory cytokines from resident cells and it has been demonstrated that over‐expression of IL‐17 plays a crucial role in the onset of several auto‐immune diseases. Here we examined the role of IL‐17 in the pathogenesis of autoimmune gastritis, a disease that was previously believed to be mediated by IFN‐γ. Significantly higher levels of IL‐17 and IFN‐γ were found in the stomachs and stomach‐draining lymph nodes of mice with severe autoimmune gastritis. Unlike IL‐17, which was produced solely by CD4⁺ T cells in gastritic mice, the majority of IFN‐γ‐producing cells were CD8⁺ T cells. However, CD8⁺ T cells alone were not able to induce autoimmune gastritis. T cells that were deficient in IL‐17 or IFN‐γ production were able to induce autoimmune gastritis but to a much lower extent compared with the disease induced by wild‐type T cells. These data demonstrate that production of neither IL‐17 nor IFN‐γ by effector T cells is essential for the initiation of autoimmune gastritis, but suggest that both are required for the disease to progress to the late pathogenic stage that includes significant tissue disruption.     

A bone‐protective role for IL‐17 receptor signaling in ovariectomy‐induced bone loss

Post‐menopausal osteoporosis is considered to be an inflammatory process, in which numerous pro‐inflammatory and T‐cell‐derived cytokines play a bone‐destructive role. IL‐17A is the signature cytokine of the pro‐inflammatory Th17 population and plays dichotomous roles in diseases that affect bone turnover. Although IL‐17A promotes bone loss in rheumatoid arthritis, it is protective against pathogen‐induced bone destruction in a periodontal disease model. We used a model of ovariectomy‐induced osteoporosis (OVX) in IL‐17 receptor (IL‐17RA)^?/? mice to evaluate the role of the IL‐17A in bone loss caused by estrogen deficiency. Unexpectedly, IL‐17RA^?/? mice were consistently and markedly more susceptible to OVX‐induced bone loss than controls. There were no changes in prototypical Th1, Th2 or Th17 cytokines in serum that could account for increased bone loss. However, IL‐17RA^?/? mice exhibited constitutively elevated leptin, which further increased following OVX. Consistently, IL‐17A and IL‐17F treatment of 3T3‐L1 pre‐adipocytes inhibited adipogenesis, leading to reduced production of leptin. In addition to its role in regulating metabolism and satiety, leptin can regulate bone turnover. Accordingly, these data show that IL‐17A negatively regulates adipogenesis and subsequent leptin expression, which correlates with increased bone destruction during OVX.     

IL‐6: Regulator of Treg/Th17 balance

IL‐6 is a pleiotropic cytokine involved in the physiology of virtually every organ system. Recent studies have demonstrated that IL‐6 has a very important role in regulating the balance between IL‐17‐producing Th17 cells and regulatory T cells (Treg). The two T‐cell subsets play prominent roles in immune functions: Th17 cell is a key player in the pathogenesis of autoimmune diseases and protection against bacterial infections, while Treg functions to restrain excessive effector T‐cell responses. IL‐6 induces the development of Th17 cells from naïve T cells together with TGF‐β; in contrast, IL‐6 inhibits TGF‐β‐induced Treg differentiation. Dysregulation or overproduction of IL‐6 leads to autoimmune diseases such as multiple sclerosis (MS) and rheumatoid arthritis (RA), in which Th17 cells are considered to be the primary cause of pathology. Given the critical role of IL‐6 in altering the balance between Treg and Th17 cells, controlling IL‐6 activities is potentially an effective approach in the treatment of various autoimmune and inflammatory diseases. Here, we review the role of IL‐6 in regulating Th17/Treg balance and describe the critical functions of IL‐6 and Th17 in immunity and immune‐pathology.     

Inhibition of Interferon Regulatory Factor 4 Suppresses Th1 and Th17 Cell Differentiation and Ameliorates Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease that is characterized by recurrent episodes of T‐cell‐mediated immune attack on central nervous system (CNS) myelin, leading to axon damage and progressive disability. Interferon regulatory factor 4 (IRF4) is expressed predominantly in the immune system and plays an important role in its development and function. Recent study demonstrated that IRF4 was critical for the generation of IL‐17‐producing Th17 cells. However, the effect of IRF4 on experimental autoimmune encephalomyelitis (EAE), an animal model of MS, needs to be further investigated. In our current study, inhibition of IRF4 with IRF4 siRNA (SiIRF4) decreases EAE scores and infiltration of Th1 and Th17 cells, but increases Treg infiltration. SiIRF4 inhibits Th1 and Th17 cell differentiation in vivo and in vitro. In our DC‐T‐cell coculture system, SiIRF4‐treated DCs resulted in significantly less IFN‐γ and IL‐17 production from T cells. Next, we adoptively transfer CD11c⁺ DCs from SiIRF4‐treated mice into recipient mice and found that these CD11c⁺ DCs ameliorated EAE. Furthermore, CD11c⁺ DCs from SiIRF4‐treated naive mice exhibited significantly reduced expression of pro‐inflammatory cytokines TNF‐α, IL‐1β, IL‐6 and IL‐12/IL‐23 (p40), and a corresponding increase in anti‐inflammatory IL‐10 expression. In conclusion, inhibition of IRF4 suppresses Th1 and Th17 cell differentiation and ameliorates EAE, via a direct regulation of DCs.     

Galectin‐9 expands immunosuppressive macrophages to ameliorate T‐cell‐mediated lung inflammation

Galectin‐9 (Gal‐9) plays pivotal roles in the modulation of innate and adaptive immunity to suppress T‐cell‐mediated autoimmune models. However, it remains unclear if Gal‐9 plays a suppressive role for T‐cell function in non‐autoimmune disease models. We assessed the effects of Gal‐9 on experimental hypersensitivity pneumonitis induced by Trichosporon asahii. When Gal‐9 was given subcutaneously to C57BL/6 mice at the time of challenge with T. asahii, it significantly suppressed T. asahii‐induced lung inflammation, as the levels of IL‐1, IL‐6, IFN‐γ, and IL‐17 were significantly reduced in the BALF of Gal‐9‐treated mice. Moreover, co‐culture of anti‐CD3‐stimulated CD4 T cells with BALF cells harvested from Gal‐9‐treated mice on day 1 resulted in diminished CD4 T‐cell proliferation and decreased levels of IFN‐γ and IL‐17. CD11b⁺Ly‐6C^highF4/80⁺ BALF M? expanded by Gal‐9 were responsible for the suppression. We further found in vitro that Gal‐9, only in the presence of T. asahii, expands CD11b⁺Ly‐6C^highF4/80⁺ cells from BM cells, and the cells suppress T‐cell proliferation and IFN‐γ and IL‐17 production. The present results indicate that Gal‐9 expands immunosuppressive CD11b⁺Ly‐6C^high M? to ameliorate Th1/Th17 cell‐mediated hypersensitivity pneumonitis.     

Lack of adiponectin leads to increased lymphocyte activation and increased disease severity in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is a presumed autoimmune disease directed against central nervous system (CNS) myelin, in which diet and obesity are implicated as risk factors. Immune responses can be influenced by molecules produced by fat cells, called adipokines. Adiponectin is an adipokine with anti‐inflammatory effects. We tested the hypothesis that adiponectin has a protective role in the EAE model for MS, that can be induced by immunization with myelin antigens or transfer of myelin‐specific T lymphocytes. Adiponectin deficient (ADPKO) mice developed worse EAE with greater CNS inflammation, demyelination, and axon injury. Lymphocytes from myelin‐immunized ADPKO mice proliferated more, produced higher amounts of IFN‐γ, IL‐17, TNF‐α, IL‐6, and transferred more severe EAE than wild type (WT) lymphocytes. At EAE peak, the spleen and CNS of ADPKO had fewer regulatory T (Treg) cells than WT mice and during EAE recovery, Foxp3, IL‐10 and TGF‐β expression levels in the CNS were reduced in ADPKO compared with WT mice. Treatment with globular adiponectin in vivo ameliorated EAE, and was associated with an increase in Treg cells. These data indicate that adiponectin is an important regulator of T‐cell functions during EAE, suggesting a new avenue of investigation for MS treatment.     

Leptin deficiency impairs maturation of dendritic cells and enhances induction of regulatory T and Th17 cells

Leptin is an adipose‐secreted hormone that plays an important role in both metabolism and immunity. Leptin has been shown to induce Th1‐cell polarization and inhibit Th2‐cell responses. Additionally, leptin induces Th17‐cell responses, inhibits regulatory T (Treg) cells and modulates autoimmune diseases. Here, we investigated whether leptin mediates its activity on T cells by influencing dendritic cells (DCs) to promote Th17 and Treg‐cell immune responses in mice. We observed that leptin deficiency (i) reduced the expression of DC maturation markers, (ii) decreased DC production of IL‐12, TNF‐α, and IL‐6, (iii) increased DC production of TGF‐β, and (iv) limited the capacity of DCs to induce syngeneic CD4⁺ T‐cell proliferation. As a consequence of this unique phenotype, DCs generated under leptin‐free conditions induced Treg or T_H17 cells more efficiently than DCs generated in the presence of leptin. These data indicate important roles for leptin in DC homeostasis and the initiation and maintenance of inflammatory and regulatory immune responses by DCs.     

Epstein–Barr virus‐induced gene 3 suppresses T helper type 1, type 17 and type 2 immune responses after Trypanosoma cruzi infection and inhibits parasite replication by interfering with alternative macrophage activation

The Epstein–Barr virus‐induced gene 3 (EBI3) is a member of the interleukin‐12 (IL)‐12) family structurally related to the subunit p40 of IL‐12 and forms a heterodimer either with the p28 subunit to build IL‐27 or with p35 to form IL‐35. Interleukin‐27 is secreted by antigen‐presenting cells whereas IL‐35 appears to be produced mainly by regulatory T cells and regulatory B cells but both cytokines negatively regulate inflammatory immune responses. We here analysed the function of EBI3 during infection with the intracellular parasite Trypanosoma cruzi. Compared with C57BL/6 wild‐type mice, EBI3‐deficient (EBI3^?/?) mice showed a higher parasitaemia associated with an increased mortality rate. The EBI3^?/? mice displayed an elevated inflammatory immune response with an increased production of T helper type 1 (Th1‐), Th2‐ and Th17‐derived cytokines. The increased Th2 immune response appears to have over‐ridden the otherwise protective Th1 and Th17 immune responses by the induction of arginase‐1‐expressing alternatively activated macrophages in these mice. Hence, neutralization of IL‐4 and arginase‐1 activity partially restored protective immune responses in EBI3^?/? mice. So far, our results demonstrate that EBI3 is an essential general regulator of inflammatory immune responses in experimental Chagas disease and is required for control of T. cruzi infection by inhibiting Th2‐dependent alternative macrophage activation. Further studies are needed to dissect the underlying mechanisms and clarify whether EBI3 association with IL‐27 or/and IL‐35 accounts for its anti‐inflammatory character in parasitic disease.     

Pathogenic T helper type 17 cells contribute to type 1 diabetes independently of interleukin‐22

We have shown that pathogenic T helper type 17 (Th17) cells differentiated from naive CD4⁺ T cells of BDC2·5 T cell receptor transgenic non‐obese diabetic (NOD) mice by interleukin (IL)‐23 plus IL‐6 produce IL‐17, IL‐22 and induce type 1 diabetes (T1D). Neutralizing interferon (IFN)‐γ during the polarization process leads to a significant increase in IL‐22 production by these Th17 cells. We also isolated IL‐22‐producing Th17 cells from the pancreas of wild‐type diabetic NOD mice. IL‐27 also blocked IL‐22 production from diabetogenic Th17 cells. To determine the functional role of IL‐22 produced by pathogenic Th17 cells in T1D we neutralized IL‐22 in vivo by using anti‐IL‐22 monoclonal antibody. We found that blocking IL‐22 did not alter significantly adoptive transfer of disease by pathogenic Th17 cells. Therefore, IL‐22 is not required for T1D pathogenesis. The IL‐22Rα receptor for IL‐22 however, increased in the pancreas of NOD mice during disease progression and based upon our and other studies we suggest that IL‐22 may have a regenerative and protective role in the pancreatic islets.     

IL-13-producing Th1 and Th17 cells characterize adaptive responses to both self and foreign antigens

In helper T cells, IL‐13 is traditionally considered a Th2‐type cytokine that is coexpressed with IL‐4. Using mouse models of immunization and autoimmunity, we demonstrate that IL‐13 is frequently uncoupled from IL‐4, and that it can be produced by both IFN‐γ⁺ Th1 cells and IL‐17⁺ Th17 cells. We report that these IL‐13‐producing Th1 and Th17 cells are distinct from classical IL‐4⁺ Th2 cells and that they are relatively common, appearing in the context of both protective and pathogenic T‐cell responses. We also demonstrate that IL‐13 and Th2‐type cytokines can have important consequences in Th1‐ and Th17‐dominated settings, such as lymphopenia‐induced autoimmune disease, where they can be either pro‐ or anti‐inflammatory, depending on whether they act on innate or adaptive immune cells. Taken together, our studies indicate that IL‐13 production is more widespread than previously appreciated and that blocking this cytokine may have therapeutic benefits even in settings where traditional IL‐4‐driven Th2‐type responses are not evident.     

EAE mediated by a non‐IFN‐γ/non‐IL‐17 pathway

Previous studies have shown that EAE can be elicited by the adoptive transfer of either IFN‐γ‐producing (Th1) or IL‐17‐producing (Th17) myelin‐specific CD4⁺ T‐cell lines. Paradoxically, mice deficient in either IFN‐γ or IL‐17 remain susceptible to EAE following immunization with myelin antigens in CFA. These observations raise questions about the redundancy of IFN‐γ and IL‐17 in autoimmune demyelinating disease mediated by a diverse, polyclonal population of autoreactive T cells. In this study, we show that an atypical form of EAE, induced in C57BL/6 mice by the adoptive transfer of IFN‐γ‐deficient effector T cells, required IL‐17 signaling for the development of brainstem infiltrates. In contrast, classical EAE, characterized by predominant spinal cord inflammation, occurred in the combined absence of IFN‐γ and IL‐17 signaling, but was dependent on GM‐CSF and CXCR2. Our findings contribute to a growing body of data, indicating that individual cytokines vary in their importance across different models of CNS autoimmunity.     

Absence of Notch1 in murine myeloid cells attenuates the development of experimental autoimmune encephalomyelitis by affecting Th1 and Th17 priming

Inhibition of Notch signalling in T cells attenuates the development of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Growing evidence indicates that myeloid cells are also key players in autoimmune processes. Thus, the present study evaluates the role of the Notch1 receptor in myeloid cells on the progression of myelin oligodendrocyte glycoprotein (MOG)_35‐55‐induced EAE, using mice with a myeloid‐specific deletion of the Notch1 gene (MyeNotch1KO). We found that EAE progression was less severe in the absence of Notch1 in myeloid cells. Thus, histopathological analysis revealed reduced pathology in the spinal cord of MyeNotch1KO mice, with decreased microglia/astrocyte activation, demyelination and infiltration of CD4⁺ T cells. Moreover, these mice showed lower Th1 and Th17 cell infiltration and expression of IFN‐γ and IL‐17 mRNA in the spinal cord. Accordingly, splenocytes from MyeNotch1KO mice reactivated in vitro presented reduced Th1 and Th17 activation, and lower expression of IL‐12, IL‐23, TNF‐α, IL‐6, and CD86. Moreover, reactivated wild‐type splenocytes showed increased Notch1 expression, arguing for a specific involvement of this receptor in autoimmune T cell activation in secondary lymphoid tissues. In summary, our results reveal a key role of the Notch1 receptor in myeloid cells for the initiation and progression of EAE.     

MicroRNA223 promotes pathogenic T‐cell development and autoimmune inflammation in central nervous system in mice

Multiple sclerosis (MS) is an incurable central nervous system autoimmune disease. Understanding MS pathogenesis is essential for the development of new MS therapies. In the present study, we identified a novel microRNA (miR) that regulates experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Expression of miR223 was up‐regulated specifically in spinal cords and lymphoid organs but not in other examined tissues. A global miR223 knockout (miR223^?/?) in mice led to a significant delay in EAE onset, reduction in spinal cord lesion, and lessening of neurological symptoms. These protective effects could be reproduced in bone marrow chimeras reconstituted with miR223^?/? haematopoietic stem cells. We also found that miR223 deficiency reduced T helper type 1 (Th1) and Th17 infiltration into spinal cords. To address underlying mechanisms, we investigated the role of miR223 in regulating the function, development and interaction of the major immune cells. Expression of the genes associated with dendritic cell (DC) activation (CD86 and MHC II) and Th1 and Th17 differentiation [interleukin‐12 (IL‐12) and IL‐23, respectively] was significantly decreased in the spleens of miR223^?/? mice bearing EAE. The miR223^?/? DCs expressed significantly lower levels of basal and lipopolysaccharide‐induced IL‐12 and IL‐23 compared with the wild‐type DCs. These data are consistent with the observed lower efficiency of miR223^?/? DCs to support Th1 and Th17 differentiation from naive T cells over‐expressing an EAE antigen‐specific T‐cell receptor. Our data suggest that miR223 promotes EAE, probably through enhancing DC activation and subsequently the differentiation of naive T cells toward Th1 and Th17 effector cells.     

Developmental maturation of innate immune cell function correlates with susceptibility to central nervous system autoimmunity

MS is an inflammatory CNS disorder, which typically occurs in early adulthood and rarely in children. Here we tested whether functional maturation of innate immune cells may determine susceptibility to CNS autoimmune disease in EAE. Two‐week‐old mice were resistant to active EAE, which causes fulminant paralysis in adult mice; this resistance was associated with an impaired development of Th1 and Th17 cells. Resistant, young mice had higher frequencies of myeloid‐derived suppressor cells and plasma‐cytoid DCs. Furthermore, myeloid APCs and B cells from young mice expressed lower levels of MHC class II and CD40, produced decreased amounts of proinflammatory cytokines, and released enhanced levels of anti‐inflammatory IL‐10. When used as APCs, splenocytes from 2‐week‐old mice failed to differentiate naive T cells into Th1 and Th17 cells irrespective of the T‐cell donor's age, and promoted development of Treg cells and Th2 cells instead. Adoptive transfer of adult APCs restored the ability of 2‐week‐old mice to generate encephalitogenic T cells and develop EAE. Collectively, these findings indicate that the innate immune compartment functionally matures during development, which may be a prerequisite for development of T‐cell‐mediated CNS autoimmune disease.     

T cells in multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a demyelinating inflammatory disorder of the central nervous system (CNS), which involves autoimmune responses to myelin antigens. Studies in experimental autoimmune encephalomyelitis (EAE), an animal model for MS, have provided convincing evidence that T cells specific for self‐antigens mediate pathology in these diseases. Until recently, T helper type 1 (Th1) cells were thought to be the main effector T cells responsible for the autoimmune inflammation. However more recent studies have highlighted an important pathogenic role for CD4⁺ T cells that secrete interleukin (IL)‐17, termed Th17, but also IL‐17‐secreting γδ T cells in EAE as well as other autoimmune and chronic inflammatory conditions. This has prompted intensive study of the induction, function and regulation of IL‐17‐producing T cells in MS and EAE. In this paper, we review the contribution of Th1, Th17, γδ, CD8⁺ and regulatory T cells as well as the possible development of new therapeutic approaches for MS based on manipulating these T cell subtypes.