Increased memory Th17 cells in patients with neuromyelitis optica and multiple sclerosis

Biomarkers for neuromyelitis optica

Neuromyelitis optica (NMO) is an acquired, heterogeneous inflammatory disorder, which is characterized by recurrent optic neuritis and longitudinally extensive spinal cord lesions. The discovery of the serum autoantibody marker, anti-aquaporin 4 (anti-AQP4) antibody, revolutionizes our understanding of pathogenesis of NMO. In addition to anti-AQP4 antibody, other biomarkers for NMO are also reported. These candidate biomarkers are particularly involved in T helper (Th)17 and astrocytic damages, which play a critical role in the development of NMO lesions. Among them, IL-6 in the peripheral blood is associated with anti-AQP4 antibody production. Glial fibrillary acidic protein (GFAP) in CSF demonstrates good correlations with clinical severity of NMO relapses. Detecting these useful biomarkers may be useful in the diagnosis and evaluation of disease activity of NMO. Development of compounds targeting these biomarkers may provide novel therapeutic strategies for NMO. This article will review the related biomarker studies in NMO and discuss the potential therapeutics targeting these biomarkers.

The treatment of neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune disorder of the central nervous system directed against astrocytes. Initially diagnosed in individuals with monophasic or relapsing optic neuritis and transverse myelitis, NMO is now recognized as a demyelinating disorder with pleiotropic presentations due to the identification of a specific autoantibody response against the astrocyte water channel aquaporin-4 in the majority of individuals. As visual impairment and neurologic dysfunction in NMO are commonly severe, aggressive treatment of relapses and prophylactic immunomodulatory therapy are the focus of treatment. Although there are no approved treatments for NMO, medications and therapeutic interventions for acute and chronic treatment have been the subject of retrospective study and case reports. The goal of this review is to familiarize the reader with biologic and clinical data supporting current treatments in NMO and highlight future strategies based on advancements in our understanding of NMO pathogenesis.

Cytokines and chemokines in neuromyelitis optica: pathogenetic and therapeutic implications

Neuromyelitis optica (NMO) is characterized by severe optic neuritis and longitudinally extensive transverse myelitis. The discovery of an NMO-specific autoantibody to the aquaporin-4 (AQP4) water channel has improved knowledge of NMO pathogenesis. Many studies have focused on inflammatory and pathological biomarkers of NMO, including cytokines and chemokines. Increased concentrations of T helper (Th)17- and Th2-related cytokines and chemokines may be essential factors for developing NMO inflammatory lesions. For example, interleukin-6 could play important roles in NMO pathogenesis, as it is involved in the survival of plasmablasts that produce anti-AQP4 antibody in peripheral circulation and in the enhancement of inflammation in the central nervous system. Therefore, assessment of these useful biomarkers may become a supportive criterion for diagnosing NMO. Significant advances in the understanding of NMO pathogenesis will lead to the development of novel treatment strategies. This review focuses on the current advances in NMO immunological research, particularly that of cytokines and chemokines.

Cannabis use by individuals with multiple sclerosis: effects on specific immune parameters

Cannabinoids affect immune responses in ways that may be beneficial for autoimmune diseases. We sought to determine whether chronic Cannabis use differentially modulates a select number of immune parameters in healthy controls and individuals with multiple sclerosis (MS cases). Subjects were enrolled and consented to a single blood draw, matched for age and BMI. We measured monocyte migration isolated from each subject, as well as plasma levels of endocannabinoids and cytokines. Cases met definition of MS by international diagnostic criteria. Monocyte cell migration measured in control subjects and individuals with MS was similarly inhibited by a set ratio of phytocannabinoids. The plasma levels of CCL2 and IL17 were reduced in non-naïve cannabis users irrespective of the cohorts. We detected a significant increase in the endocannabinoid arachidonoylethanolamine (AEA) in serum from individuals with MS compared to control subjects, and no significant difference in levels of other endocannabinoids and signaling lipids irrespective of Cannabis use. Chronic Cannabis use may affect the immune response to similar extent in individuals with MS and control subjects through the ability of phytocannabinoids to reduce both monocyte migration and cytokine levels in serum. From a panel of signaling lipids, only the levels of AEA are increased in individuals with MS, irrespective of Cannabis use or not. Our results suggest that both MS cases and controls respond similarly to chronic Cannabis use with respect to the immune parameters measured in this study.

Treatment of neuromyelitis optica: state-of-the-art and emerging therapies

Neuromyelitis optica (NMO) is an autoimmune disease of the CNS that is characterized by inflammatory demyelinating lesions in the spinal cord and optic nerve, potentially leading to paralysis and blindness. NMO can usually be distinguished from multiple sclerosis (MS) on the basis of seropositivity for IgG antibodies against the astrocytic water channel aquaporin-4 (AQP4). Differentiation from MS is crucial, because some MS treatments can exacerbate NMO. NMO pathogenesis involves AQP4-IgG antibody binding to astrocytic AQP4, which causes complement-dependent cytotoxicity and secondary inflammation with granulocyte and macrophage infiltration, blood-brain barrier disruption and oligodendrocyte injury. Current NMO treatments include general immunosuppressive agents, B-cell depletion, and plasma exchange. Therapeutic strategies targeting complement proteins, the IL-6 receptor, neutrophils, eosinophils and CD19--all initially developed for other indications--are under clinical evaluation for repurposing for NMO. Therapies in the preclinical phase include AQP4-blocking antibodies and AQP4-IgG enzymatic inactivation. Additional, albeit currently theoretical, treatment options include reduction of AQP4 expression, disruption of AQP4 orthogonal arrays, enhancement of complement inhibitor expression, restoration of the blood-brain barrier, and induction of immune tolerance. Despite the many therapeutic options in NMO, no controlled clinical trials in patients with this condition have been conducted to date.

Increased Th17 cells and IL‑17 in rats with traumatic optic neuropathy

T helper 17 (Th17) cells are strong inducers of numerous autoimmune diseases and inflammation. However, the role of Th17 cells and interleukin (IL)‑17 in traumatic optic neuropathy (TON) are yet to be elucidated. In the present study, a rat model of TON was established using a fluid percussion brain injury device. Th17 cells were found to be upregulated in the spleens of rats in the TON group. In addition, the level of IL‑17 in the retina of rats in the TON group was observed to increase with the upregulation of the Th17 cells. Furthermore, the expression of IL‑17 in the optic nerve was found to be upregulated between one and seven days following injury in the rats in the TON group. These findings strongly suggest that the ratio of Th17 cells and the expression of IL‑17 are upregulated in rats with TON. These findings also provide a rationale for developing therapeutic agents to treat TON.

Th17 cells in autoimmune and infectious diseases

The view of CD4 T-cell-mediated immunity as a balance between distinct lineages of Th1 and Th2 cells has changed dramatically. Identification of the IL-17 family of cytokines and of the fact that IL-23 mediates the expansion of IL-17-producing T cells uncovered a new subset of Th cells designated Th17 cells, which have emerged as a third independent T-cell subset that may play an essential role in protection against certain extracellular pathogens. Moreover, Th17 cells have been extensively analyzed because of their strong association with inflammatory disorders and autoimmune diseases. Also, they appear to be critical for controlling these disorders. Similar to Th1 and Th2 cells, Th17 cells require specific cytokines and transcription factors for their differentiation. Th17 cells have been characterized as one of the major pathogenic Th cell populations underlying the development of many autoimmune diseases, and they are enhanced and stabilized by IL-23. The characteristics of Th17 cells, cytokines, and their sources, as well as their role in infectious and autoimmune diseases, are discussed in this review.

Monoclonal antibodies in treatment of multiple sclerosis

Monoclonal antibodies (mAbs) are used as therapeutics in a number of disciplines in medicine, such as oncology, rheumatology, gastroenterology, dermatology and transplant rejection prevention. Since the introduction and reintroduction of the anti-alpha4-integrin mAb natalizumab in 2004 and 2006, mAbs have gained relevance in the treatment of multiple sclerosis (MS). At present, numerous mAbs have been tested in clinical trials in relapsing-remitting MS, and in progressive forms of MS. One of the agents that might soon be approved for very active forms of relapsing-remitting MS is alemtuzumab, a humanized mAb against CD52. This review provides insights into clinical studies with the mAbs natalizumab, alemtuzumab, daclizumab, rituximab, ocrelizumab and ofatumumab.

Cytokine production profiles in chronic relapsing-remitting experimental autoimmune encephalomyelitis: IFN-γ and TNF-α are important participants in the first attack but not in the relapse

Multiple sclerosis (MS) is a chronic demyelinating disease often displaying a relapsing-remitting course of neurological manifestations that is mimicked by experimental autoimmune encephalomyelitis (EAE) in animal models of MS. In particular, NOD mice immunized with myelin oligodendrocyte glycoprotein peptide 35-55 develop chronic relapsing-remitting EAE (CREAE). To elucidate the mechanisms that cause MS relapse, we investigated the histopathology and cytokine production of spleen cells and mRNA expression levels in the central nervous system (CNS) of CREAE mice. During the first attack, inflammatory cell infiltration around small vessels and in the subarachnoid space was observed in the spinal cord. Spleen cell production and mRNA expression in the CNS of several cytokines, including IFN-γ, TNF-α, IL-6, IL-17, and CC chemokine ligand 2 (CCL2), were higher in CREAE mice than in controls. Afterwards, parenchymal infiltration and demyelination were observed histologically in the spinal cord and corresponded with the more severe clinical symptoms of the first and second relapses. IL-17 and CCL2, but not IFN-γ, TNF-α, or IL-6, were also produced by spleen cells during recurrences. Our results suggested that the immune mechanisms in relapses were different from those in the first attack for CREAE. Further investigation of CREAE mechanisms may provide important insights into successful therapies for human relapsing-remitting MS.

Immunotherapy of neuromyelitis optica

Neuromyelitis optica (NMO) is a chronic inflammatory disease of the central nervous system that affects the optic nerves and spinal cord resulting in visual impairment and myelopathy. There is a growing body of evidence that immunotherapeutic agents targeting T and B cell functions, as well as active elimination of proinflammatory molecules from the peripheral blood circulation, can attenuate disease progression. In this review, we discuss the immunotherapeutic options and the treatment strategies in NMO. We also analyze the pathogenic mechanisms of the disease in order to provide recommendations regarding treatments.

The plasticity of human Treg and Th17 cells and its role in autoimmunity

CD4(+) T helper cells are a central element of the adaptive immune system. They protect the organism against a wide range of pathogens and are able to initiate and control many immune reactions in combination with other cells of the adaptive and the innate immune system. Starting from a naive cell, CD4(+) T cells can differentiate into various effector cell populations with specialized function. This subset specific differentiation depends on numerous signals and the strength of stimulation. However, recent data have shown that differentiated CD4(+) T cell subpopulations display a high grade of plasticity and that their initial differentiation is not an endpoint of T cell development. In particular, FoxP3(+) regulatory T cells (Treg) and Th17 effector T cells demonstrate a high grade of plasticity, which allow a functional adaptation to various physiological situations during an immune response. However, the plasticity of Treg and Th17 cells might also be a critical factor for autoimmune disease. Here we discuss the recent developments in CD4(+) T cell plasticity with a focus on Treg and Th17 cells and its role in human autoimmune disease, in particular multiple sclerosis (MS).

Distinct serum cytokine profiles in neuromyelitis optica and multiple sclerosis

Multiple sclerosis (MS) is the most common prototypic inflammatory demyelinating disease. Neuromyelitis optica (NMO) is another inflammatory demyelinating disease of the central nervous system that exhibits clinical symptoms mainly associated with optic neuritis and myelopathy. The inflammatory reaction in MS is associated with an upregulation of a variety of T helper 1 (Th1)- or Th17-mediated cytokines. However, NMO and MS are intertwined both clinically and pathologically, which complicates their diagnosis and treatment. The aim of this study was to evaluate the differences in serum cytokine levels in patients with NMO and MS. We collected peripheral serum from patients with these central nervous system demyelinating diseases for the study. A cytometric bead array was used to assess the cytokine levels using flow cytometry. We found more inflammatory [interleukin (IL)-2 and interferon-γ) and anti-inflammatory (IL-4 and IL-10) cytokines in NMO than in MS. The differences in the optimal cutoff points of serum cytokines, including IL-2 ≥5 pg/mL, can differentiate NMO from MS. In conclusion, patients with NMO had an increased Th1-mediated inflammatory response, but similar Th17-mediated inflammation changes compared to patients with MS. Serum cytokine studies can differentiate NMO cases from MS.

IL-22 secreting CD4+ T cells in the patients with neuromyelitis optica and multiple sclerosis

Interleukin (IL)-22 secreting CD4(+) T (Th22) cells and IL-22 are involved in the pathogenesis of autoimmune disease, but their role in neuromyelitis optica (NMO) and multiple sclerosis (MS) is unclear. We measured the proportion of Th22, Th17, CD4(+)IL-22(+)IL-17A(+) T cells and serum IL-22 in NMO and MS patients. The proportion of Th22 cells, Th17 cells and serum IL-22 were increased in patients with NMO and MS. Our findings suggest that increased Th22 cells may play an important role in the pathogenesis of NMO and MS.

Cerebrospinal fluid IL-21 levels in Neuromyelitis Optica and multiple sclerosis

BACKGROUND

Neuromyelitis optica (NMO) and multiple sclerosis (MS) are inflammatory demyelinating diseases of human central nervous system (CNS) with complex pathogenesis. IL-21/IL-21R regulates activation, proliferation and survival of both T cells and B cells, which are involved in the pathogenesis of NMO and MS. High levels of serum IL-21 were observed in NMO patients. However, concentration of cerebrospinal fluid (CSF) IL-21 in MS and NMO patients still remain unknown.

OBJECT

To detect the CSF concentration of IL-21 in NMO and MS patients and to evaluate its relationship with disease activity, particularly concerned about its impact on humoral immunity.

METHODS

CSF IL-21 was detected by an enzyme-linked immunosorbent assay (ELISA) in NMO patients (n=21), MS patients (n=20) and controls (n=16).

RESULTS

CSF concentration of the IL-21 was noticeably elevated in NMO (p=0.012) and borderline significantly increased in MS (p=0.115). In addition, this occurrence was associated with humoral immune activity as shown by a correlation between IL-21 and complement in NMO cohort (p=0.023) and high IL-21 levels in autoantibody-positive subgroup (p=0.027).

CONCLUSIONS

The concentration of CSF IL-21 was noticeably elevated and might have a positive correlation with humoral immune activity in NMO.

Cerebrospinal fluid high-mobility group box protein 1 in neuromyelitis optica and multiple sclerosis

BACKGROUND

Neuromyelitis optica (NMO) and multiple sclerosis (MS) are two autoimmune inflammatory demyelinating diseases in the central nervous system. Interleukin (IL)-6 and IL-17 may play important roles in the pathogenesis of these diseases. High-mobility group box protein 1 (HMGB1) can activate the nuclear factor light chain enhancer of activated B cells and release cytokines such as IL-6 and IL-17. However, whether cerebrospinal fluid (CSF) HMGB1 levels were altered in NMO and MS patients is still unclear.

OBJECTIVES

It was our aim to measure the CSF HMGB1 concentration in NMO patients and explore their relationship with IL-6, IL-17 and disease activity.

METHODS

CSF HMGB1 was measured by enzyme-linked immunosorbent assay in NMO (n = 22) and MS (n = 18) patients as well as in controls (n = 14).

RESULTS

CSF HMGB1 was notably higher in the NMO group compared with controls (p = 0.007). CSF HMGB1 positively correlated with IL-6 and IL-17 in NMO patients (IL-6, p = 0.034; IL-17, p < 0.001).

CONCLUSIONS

In conclusion, our study suggests that CSF levels of HMGB1 are increased in patients with NMO and reflect the neuroinflammatory process.

Molecular pathogenesis of neuromyelitis optica

Neuromyelitis optica (NMO) is a rare autoimmune disorder, distinct from multiple sclerosis, causing inflammatory lesions in the optic nerves and spinal cord. An autoantibody (NMO IgG) against aquaporin-4 (AQP4), a water channel expressed on astrocytes is thought to be causative. Peripheral production of the antibody is triggered by an unknown process in genetically susceptible individuals. Anti-AQP4 antibody enters the central nervous system (CNS) when the blood brain barrier is made permeable and has high affinity for orthogonal array particles of AQP4. Like other autoimmune diseases, Th17 cells and their effector cytokines (such as interleukin 6) have been implicated in pathogenesis. AQP4 expressing peripheral organs are not affected by NMO IgG, but the antibody causes extensive astrocytic loss in specific regions of the CNS through complement mediated cytotoxicity. Demyelination occurs during the inflammatory process and is probably secondary to oligodendrocyte apoptosis subsequent to loss of trophic support from astrocytes. Ultimately, extensive axonal injury leads to severe disability. Despite rapid advances in the understanding of NMO pathogenesis, unanswered questions remain, particularly with regards to disease mechanisms in NMO IgG seronegative cases. Increasing knowledge of the molecular pathology is leading to improved treatment strategies.

Cross-immunoreactivity between bacterial aquaporin-Z and human aquaporin-4: potential relevance to neuromyelitis optica

Neuromyelitis optica (NMO) is a chronic inflammatory disease of the CNS that is mediated, in part, by a self-reactive Ab against the astrocyte aquaporin-4 protein. In the current study, we examined the possibility and the biological significance of cross-immunoreactivity between bacterial aquaporin-Z and human aquaporin-4 proteins. Sequence-alignment analysis of these proteins revealed several regions of significant structural homology. Some of the homologous regions were also found to overlap with important immune and disease-relevant epitopes. Cross-immunoreactivity between aquaporin-Z and aquaporin-4 was investigated and ascertained in multiple immune-based assays using sera from patients with neuromyelitis optica, immune mouse serum, and Abs raised against aquaporin-Z. The biological significance of this phenomenon was established in series of experiments demonstrating that induction of an immune response against aquaporin-Z or its homologous regions can also trigger an autoimmune reaction against aquaporin-4 and inflammation of the CNS. Our study indicates that the autoimmune response against aquaporin-4 in neuromyelitis optica may be triggered by infection-induced cross-immunoreactivity and presents a new perspective on the pathogenesis of this disease.

The ex vivo production of IL-6 and IL-21 by CD4+ T cells is directly associated with neurological disability in neuromyelitis optica patients

Neuromyelitis optica (NMO), also known as Devic's disease, is an autoimmune, inflammatory disorder of the central nervous system (CNS) in which the immune system attacks myelin of the neurons located at the optic nerves and spinal cord, thus producing a simultaneous or sequential optic neuritis and myelitis. The objective of this study was evaluated the background T-cell function of patients suffering from neuromyelitis optica (NMO), an autoimmune disorder of the central nervous system. In our study, the in vitro T cell proliferation and the production of Th1 cytokines were significantly lower in cell cultures from NMO patients, as compared with healthy individuals. In contrast, a dominant Th17-like phenotype, associate with higher IL-23 and IL-6 production by LPS-activated monocytes, was observed among NMO patients. The release of IL-21 and IL-6 by polyclonally activated CD4+ T cells was directly correlated to neurological disability. In addition, the in vitro release of IL-21, IL-6 and IL-17 was significantly more resistant to glucocorticoid inhibition in NMO patients. In conclusion, the results indicate dominant Th17-related response in NMO patients that was directly proportional to neurological disability. Furthermore, our results can help to explain why NMO patients trend to be more refractory to corticoid treatment.

Where Do AQP4 Antibodies Fit in the Pathogenesis of NMO?

Recent advances in the field of neuromyelitis optica (NMO) research provided convincing evidence that anti-AQP4 antibody (AQP4-Ab) not only serves as a highly specific disease marker, but also plays an essential role in the pathogenesis of the disease. Although it is now widely recognized that AQP4-Ab induces astrocytic necrosis in a complement-dependent manner, additional triggers are also suspected as a prerequisite for the development of the disease. Unraveling these unresolved aspects of the disease will provide substantial insight into still controversial issues in the pathogenesis of NMO.

Notable increased cerebrospinal fluid levels of soluble interleukin-6 receptors in neuromyelitis optica

BACKGROUND

IL-6 is a proinflammatory cytokine which is involved in the maintenance of the humoral response in various autoimmune disorders. Cerebrospinal fluid (CSF) IL-6 has shown to be increased in neuromyelitis optica (NMO). The soluble form of IL-6 receptor (sIL-6R), which links to IL-6, can activate biological responses in cells. Whether or not sIL-6R is altered in NMO has not been clarified.

OBJECTIVE

To measure CSF IL-6 and sIL-6R in NMO and multiple sclerosis (MS) patients, and investigate whether IL-6 and sIL-6R have possible uses as sensitive biomarkers for diseases activity.

METHODS

CSF concentrations of IL-6 and sIL-6R were measured by an ELISA in NMO (n = 22) and MS (n = 18) patients, as well as control subjects (n = 14).

RESULTS

The concentration of IL-6 levels were higher in NMO compared to MS (p = 0.032) and the controls (p = 0.023). The levels of sIL-6R were also higher in NMO compared to MS (p = 0.002) and the controls (p < 0.001). CSF sIL-6R was associated with an Expanded Disability Status Scale score in NMO (p = 0.005) but not in MS (p = 0.891). In the MS subgroup, sIL-6R concentrations were associated with CSF white blood cells (p = 0.034).

CONCLUSIONS

Our study revealed that CSF sIL-6R was increased in NMO patients, and correlated with clinical presentations.

Interleukin 17 gene polymorphism is associated with anti-aquaporin 4 antibody-positive neuromyelitis optica in the Southern Han Chinese--a case control study

BACKGROUND

Interleukin 17 (IL-17) plays an important role in many autoimmune diseases including neuromyelitis optica (NMO) and multiple sclerosis (MS), which are inflammatory demyelinating diseases of the central nervous system. A large number of non-HLA single nucleotide polymorphisms have been reported to increase the risk of MS. However, their effects on NMO have been less well studied.

METHODS

Fifty-two anti-aquaporin 4 antibody-positive NMO patients, 69 anti-aquaporin 4 antibody-negative conventional MS patients, and 131 controls were genotyped for the IL-17A rs2275913 and IL-17F rs763780 single nucleotide polymorphisms by DNA sequencing.

RESULTS

Significantly higher frequencies of the rs763780 T allele (p(uncorr)=0.011) and TT genotype (p(uncorr)=0.007, p(corr)=0.042) were observed in NMO patients versus controls.

CONCLUSIONS

The rs763780 T allele and TT genotype may increase susceptibility to NMO in the Southern Han Chinese.

Cerebrospinal fluid levels of CXCL13 are elevated in neuromyelitis optica

BACKGROUND

B cells are believed to play an important role in the pathogenesis of NMO. Chemokine (C-X-C motif) ligand 13 (CXCL13), the most potent B-cell chemoattractant, is a chemokine which is critical for secondary lymphoid tissue development and for B-cell migration. Concentration of CXCL13 in cerebral spinal fluid (CSF) is elevated in patients with multiple sclerosis (MS). However, whether levels of CSF CXCL13 are elevated in NMO patients still remain unknown.

OBJECTIVE

To measure the CSF concentration of CXCL13 in NMO patients, and to determine its relationship with NMO disease activity.

METHODS

CSF CXCL13 was measured by an enzyme-linked immunosorbent assay (ELISA) in NMO (n=22), MS (n=18) patients and controls (CTLs) (n=12).

RESULTS

CSF CXCL13 levels in NMO were notable higher than MS (p=0.015) and CTLs (p<0.001), and were related to the NMO disease activity indicated by relapse rate and Expanded Disability Status Scale (EDSS) scores. NMO Patients with the higher relapse rates exhibited the higher CXCL13 concentrations in their CSF; and a trend of increased disease disability with increased CSF CXCL13 level was revealed. The CSF CXCL13 concentrations seemed to associate with CSF white blood cell counting, total protein concentration in NMO subgroup, thought did not quite reach statistical significance (WBC, p=0.473; TP, p=0.276).

CONCLUSIONS

The concentration of CSF CXCL13 was elevated in NMO patients, and correlated with NMO activity.

T(H)17 cytokines in autoimmune neuro-inflammation

It has been firmly established that IL-23 polarized T(H)17 cells are potent effectors in the pathogenesis of experimental autoimmune encephalitomyelitis (EAE). However, the relative importance of these cells in comparison to other encephalitogenic T(H) subsets, and the mechanisms that they employ to effect inflammatory demyelination, are topics of continuing investigation. Interestingly, deletion of individual 'T(H)17 cytokines', such as IL-17A, IL-17F, IL-22 and IL-21, does not phenocopy the complete EAE-resistance of IL-23-deficient mice. The instability of T(H)17 cells in vivo introduces an additional layer of complexity to their role in the context of relapsing or chronic disease. Recent data indicate that IL-23 drives the production of myeloid activating factors, such as GM-CSF, by myelin-reactive T cells and facilitates their accumulation in the CNS. This review discusses the above issues in relation to the use of T(H)17 cells and related factors as potential therapeutic targets and biomarkers in CNS autoimmune diseases such as multiple sclerosis (MS).

T(H)17 cytokines in autoimmune neuro-inflammation

It has been firmly established that IL-23 polarized T(H)17 cells are potent effectors in the pathogenesis of experimental autoimmune encephalitomyelitis (EAE). However, the relative importance of these cells in comparison to other encephalitogenic T(H) subsets, and the mechanisms that they employ to effect inflammatory demyelination, are topics of continuing investigation. Interestingly, deletion of individual 'T(H)17 cytokines', such as IL-17A, IL-17F, IL-22 and IL-21, does not phenocopy the complete EAE-resistance of IL-23-deficient mice. The instability of T(H)17 cells in vivo introduces an additional layer of complexity to their role in the context of relapsing or chronic disease. Recent data indicate that IL-23 drives the production of myeloid activating factors, such as GM-CSF, by myelin-reactive T cells and facilitates their accumulation in the CNS. This review discusses the above issues in relation to the use of T(H)17 cells and related factors as potential therapeutic targets and biomarkers in CNS autoimmune diseases such as multiple sclerosis (MS).