Optical coherence tomography angiography indicates subclinical retinal disease in neuromyelitis optica spectrum disorders

Background:

Neuromyelitis optica spectrum disorders (NMOSD) are neuroinflammatory diseases of the central nervous system. Patients suffer from recurring relapses and it is unclear whether relapse-independent disease activity occurs and whether this is of clinical relevance.

Objective:

To detect disease-specific alterations of the retinal vasculature that reflect disease activity during NMOSD.

Methods:

Cross-sectional analysis of 16 patients with NMOSD, 21 patients with relapsing-remitting multiple sclerosis, and 21 healthy controls using retinal optical coherence tomography (OCT), optical coherence tomography angiography (OCT-A), measurement of glial fibrillary acidic protein (GFAP) serum levels, and assessment of visual acuity.

Results:

Patients with NMOSD but not multiple sclerosis revealed lower foveal thickness (FT) (p = 0.02) measures and an increase of the foveal avascular zone (FAZ) (p = 0.02) compared to healthy controls independent to optic neuritis. Reduced FT (p = 0.01), enlarged FAZ areas (p = 0.0001), and vessel loss of the superficial vascular complex (p = 0.01) were linked to higher serum GFAP levels and superficial vessel loss was associated with worse visual performance in patients with NMOSD irrespective of optic neuritis.

Conclusion:

Subclinical parafoveal retinal vessel loss might occur during NMOSD and might be linked to astrocyte damage and poor visual performance. OCT-A may be a tool to study subclinical disease activity during NMOSD.

Formation and immunomodulatory function of meningeal B cell aggregates in progressive CNS autoimmunity

Meningeal B lymphocyte aggregates have been described in autopsy material of patients with chronic multiple sclerosis. The presence of meningeal B cell aggregates has been correlated with worse disease. However, the functional role of these meningeal B cell aggregates is not understood. Here, we use a mouse model of multiple sclerosis, the spontaneous opticospinal encephalomyelitis model, which is built on the double transgenic expression of myelin oligodendrocyte glycoprotein-specific T-cell and B-cell receptors, to show that the formation of meningeal B cell aggregates is dependent on the expression of α4 integrins by antigen-specific T cells. T cell-conditional genetic ablation of α4 integrins in opticospinal encephalomyelitis mice impaired the formation of meningeal B cell aggregates, and surprisingly, led to a higher disease incidence as compared to opticospinal encephalomyelitis mice with α4 integrin-sufficient T cells. B cell-conditional ablation of α4 integrins in opticospinal encephalomyelitis mice resulted in the entire abrogation of the formation of meningeal B cell aggregates, and opticospinal encephalomyelitis mice with α4 integrin-deficient B cells suffered from a higher disease burden than regular opticospinal encephalomyelitis mice. While anti-CD20 antibody-mediated systemic depletion of B cells in opticospinal encephalomyelitis mice after onset of disease failed to efficiently decrease meningeal B cell aggregates without significantly modulating disease progression, treatment with anti-CD19 chimeric antigen receptor-T cells eliminated meningeal B cell aggregates and exacerbated clinical disease in opticospinal encephalomyelitis mice. Since about 20% of B cells in organized meningeal B cell aggregates produced either IL-10 or IL-35, we propose that meningeal B cell aggregates might also have an immunoregulatory function as to the immunopathology in adjacent spinal cord white matter. The immunoregulatory function of meningeal B cell aggregates needs to be considered when designing highly efficient therapies directed against meningeal B cell aggregates for clinical application in multiple sclerosis.

Inner retinal layer thinning in radiologically isolated syndrome predicts conversion to multiple sclerosis

BACKGROUND AND PURPOSE

Individuals with radiologically isolated syndrome (RIS) are at increased risk of converting to multiple sclerosis (MS). Early identification of later converters is crucial for optimal treatment decisions. The purpose of this study was to assess the predictive potential of optical coherence tomography (OCT) measures in individuals with RIS regarding conversion to MS.

METHODS

This prospective observational cohort study included 36 individuals with RIS and 36 healthy controls recruited from two German MS centers. All individuals received baseline OCT and clinical examination and were longitudinally followed over up to 6 years. The primary outcome measure was the conversion to MS.

RESULTS

During clinical follow-up of 46 (26-58) months (median, 25%-75% interquartile range), eight individuals with RIS converted to MS. Individuals converting to MS showed a thinning of the peripapillary retinal nerve fiber layer (pRNFL) and the common ganglion cell and inner plexiform layer (GCIP) at baseline and during follow-up. Individuals with a pRNFL of 99 µm or lower or a GCIP of 1.99 mm³ or lower were at a 7.5- and 8.0-fold risk for MS conversion, respectively, compared to individuals with higher measures. After correction for other known risk factors, Cox proportional hazards regression revealed a hazard ratio of 1.08 for conversion to MS for each 1 µm decline in pRNFL.

CONCLUSIONS

Reduction of the pRNFL might be a novel and independent risk factor for conversion to MS in individuals with RIS. OCT might be useful for risk stratification and therapeutic decision-making in individuals with RIS.

Tertiary Lymphoid Organs in Central Nervous System Autoimmunity

Multiple sclerosis (MS) is an autoimmune disease characterized by chronic inflammation in the central nervous system (CNS), which results in permanent neuronal damage and substantial disability in patients. Autoreactive T cells are important drivers of the disease; however, the efficacy of B cell depleting therapies uncovered an essential role for B cells in disease pathogenesis. They can contribute to inflammatory processes via presentation of autoantigen, secretion of pro-inflammatory cytokines, and production of pathogenic antibodies. Recently, B cell aggregates reminiscent of tertiary lymphoid organs (TLOs) were discovered in the meninges of MS patients, leading to the hypothesis that differentiation and maturation of autopathogenic B and T cells may partly occur inside the CNS. Since these structures were associated with a more severe disease course, it is extremely important to gain insight into the mechanism of induction, their precise function, and clinical significance. Mechanistic studies in patients are limited. However, a few studies in the MS animal model experimental autoimmune encephalomyelitis (EAE) recapitulate TLO formation in the CNS and provide new insight into CNS TLO features, formation, and function. This review summarizes what we know so far about CNS TLOs in MS and what we have learned about them from EAE models. It also highlights the areas that are in need of further experimental work, as we are just beginning to understand and evaluate the phenomenon of CNS TLOs.

IL-21R signaling is critical for induction of spontaneous experimental autoimmune encephalomyelitis

IL-17-producing CD4+ T cells (Th17 cells) have well-described pathogenic roles in tissue inflammation and autoimmune diseases, such as experimental autoimmune encephalomyelitis (EAE); however, the involvement of IL-21 in these processes has remained controversial. While IL-21 is an essential autocrine amplification factor for differentiation of Th17 cells, the loss of IL-21 or IL-21 receptor (IL-21R) does not protect mice from actively induced EAE. Here, we utilized a transgenic EAE mouse model, in which T and B cells overexpress receptors for myelin oligodendrocyte glycoprotein (MOG) (referred to as 2D2xTH mice), and demonstrated that IL-21 is critical for the development of a variant form of spontaneous EAE in these animals. Il21r deletion in 2D2xTH mice reduced the incidence and severity of spontaneous EAE, which was associated with a defect in Th17 cell generation. Moreover, IL-21R deficiency limited IL-23R expression on Th17 cells and inhibited expression of key molecules involved in the generation of pathogenic Th17 cells. Conversely, loss of IL-23R in 2D2xTH mice resulted in complete resistance to the development of spontaneous EAE. Our data identify a previously unappreciated role for IL-21 in EAE and reveal that IL-21-mediated signaling supports generation and stabilization of pathogenic Th17 cells and development of spontaneous autoimmunity.

Immunology of neuromyelitis optica: a T cell-B cell collaboration

Neuromyelitis optica (NMO) is a debilitating autoimmune inflammatory disease of the central nervous system (CNS) that is distinct from multiple sclerosis (MS). The discovery of NMO-immunoglobulin G (IgG) in the serum of NMO-but not MS-patients was a breakthrough in defining diagnostic criteria for NMO. NMO-IgG is an antibody directed against the astrocytic water channel protein aquaporin-4 (AQP4). While there is evidence that NMO-IgG is also involved in mediating tissue damage in the CNS, many aspects of the pathogenic cascade in NMO remain to be determined. It is clear that antigen-specific T cells contribute to the generation of NMO-IgG in the peripheral immune compartment, as well as to the development of NMO lesions in the CNS. T helper 17 (Th17) cells, equipped both in providing B cell help and inducing tissue inflammation, may be involved in NMO development and pathogenesis. Here, we review immunologic aspects of NMO, placing recent findings in the biology of T-B cell cooperation into perspective with autoimmunity of the CNS.

Th17 cells induce ectopic lymphoid follicles in central nervous system tissue inflammation

Ectopic lymphoid follicles are hallmarks of chronic autoimmune inflammatory diseases such as multiple sclerosis (MS), rheumatoid arthritis, Sjögren's syndrome, and myasthenia gravis. However, the effector cells and mechanisms that induce their development are unknown. Here we showed that in experimental autoimmune encephalomyelitis (EAE), the animal model of MS, Th17 cells specifically induced ectopic lymphoid follicles in the central nervous system (CNS). Development of ectopic lymphoid follicles was partly dependent on the cytokine interleukin 17 (IL-17) and on the cell surface molecule Podoplanin (Pdp), which was expressed on Th17 cells, but not on other effector T cell subsets. Pdp was also crucial for the development of secondary lymphoid structures: Pdp-deficient mice lacked peripheral lymph nodes and had a defect in forming normal lymphoid follicles and germinal centers in spleen and lymph node remnants. Thus, Th17 cells are uniquely endowed to induce tissue inflammation, characterized by ectopic lymphoid follicles within the target organ.

IL-23 receptor regulates unconventional IL-17-producing T cells that control bacterial infections

IL-23 plays an important role in autoimmune tissue inflammation and induces the generation of not fully characterized effector cells that mediate protection against pathogens. In this paper, we established the essential role of IL-23R in the host response against intracellular pathogens. IL-23 was critical for the expansion or maintenance of gammadelta and double negative (DN) alphabeta T cells. These cells were rapidly recruited to the site of infection and produced large amounts of IL-17, IFN-gamma, and TNF-alpha. Notably, DN T cells transferred into L. monocytogenes-infected RAG2(-/-) mice prevented bacterial growth, confirming their protective role against intracellular pathogens. Our results show that IL-23 regulates the function of IL-17-producing gammadelta and DN T cells, two essential components of the early protective immune response directed against intracellular pathogens.

Immunological basis for the development of tissue inflammation and organ-specific autoimmunity in animal models of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for multiple sclerosis (MS) that has shaped our understanding of autoimmune tissue inflammation in the central nervous system (CNS). Major therapeutic approaches to MS have been first validated in EAE. Nevertheless, EAE in all its modifications is not able to recapitulate the full range of clinical and histopathogenic aspects of MS. Furthermore, autoimmune reactions in EAE-prone rodent strains and MS patients may differ in terms of the relative involvement of various subsets of immune cells. However, the role of specific molecules that play a role in skewing the immune response towards pathogenic autoreactivity is very similar in mice and humans. Thus, in this chapter, we will focus on the identification of a novel subset of inflammatory T cells, called Th17 cells, in EAE and their interplay with other immune cells including protective regulatory T cells (T-regs). It is likely that the discovery of Th17 cells and their relationship with T-regs will change our understanding of organ-specific autoimmune diseases in the years to come.

IL-4 inhibits TGF-beta-induced Foxp3+ T cells and, together with TGF-beta, generates IL-9+ IL-10+ Foxp3(-) effector T cells

Foxp3 is a key transcription factor involved in the generation and function of regulatory T (T_reg) cells. Transforming growth factor β (TGF-β) induces Foxp3, which generates inducible Foxp3⁺ T_reg cells from naïve T cells, and interleukin 6 (IL-6) inhibits the generation of inducible T_reg cells and induces T helper cells that produce IL-17 (T_H-17 cells). However, a role for IL-4 in the generation of TGF-β-induced T_reg cells and/or the generation of effector CD4⁺ T helper cells has not been studied. Here, we show that IL-4 blocked the generation of TGF-β-induced Foxp3⁺ T_reg cells. Instead, IL-4 induced a population of T helper cells that predominantly produce IL-9 and IL-10. The IL-9⁺IL-10⁺ T cells did not exhibit any regulatory properties in spite of producing large quantities of IL-10. Adoptive transfer of IL-9⁺IL-10⁺producing T cells into RAG-1-deficient mice induced colitis and peripheral neuritis. Interestingly, the severity of tissue inflammation was aggravated when IL-9⁺IL-10⁺ T cells were co-transferred with CD45RB^hi CD4⁺ effector T cells into RAG-1-deficient mice, which indicated that IL-9⁺IL-10⁺ T cells do not display any suppressive function and therefore constitute a unique population of IL-10-producing helper-effector T cells that promote tissue inflammation.

Monocyte-derived HLA-G acts as a strong inhibitor of autologous CD4 T cell activation and is upregulated by interferon-β in vitro and in vivo: rationale for the therapy of multiple sclerosis

Peripheral antigen presenting cells (APCs) contribute to the maintenance of immune tolerance and are considered to play a critical role in promoting the (re)activation of autoreactive T cells in multiple sclerosis (MS). Interferon-beta (IFN-beta) is the principle immune-modulatory agent used in the treatment of MS, but its mechanism of action remains elusive. HLA-G is a non-classical MHC molecule (MHC class Ib) attributed chiefly immune-regulatory functions. We here investigated the role of monocyte-derived HLA-G in the immune-regulatory processes of MS and its implications for current immune-modulatory therapies. Monocytes constitutively express cell surface HLA-G1 and soluble HLA-G5. Comparison of monocytic HLA-G expression between patients with relapsing-remitting MS (n=17) and healthy donors (n=20) revealed significantly lower levels of HLA-G1 protein in MS patients. However, both groups showed a significant upregulation of HLA-G in response to IFN-beta in vitro. Serial measurements of HLA-G mRNA levels in MS patients before and during IFN-beta therapy corroborated the relevance of these results in vivo: 1 month after initiation of IFN-beta1b therapy (n=9), HLA-G1 and HLA-G5 were significantly increased compared to baseline levels and remained elevated during treatment for 6 months (n=3). Importantly, functional experiments demonstrated that monocyte-derived HLA-G inhibits both Th1 (IFN-gamma, IL-2) and Th2 (IL-10) cytokine production by antigen-stimulated autologous CD4 T cells. Soluble HLA-G added to antigen-specific T cell lines (TCLs) has similar effects on the release of cytokines and reduces T cell proliferation. Although both IFN-beta and IFN-gamma strongly enhance HLA-G1 and HLA-G5 expression by monocytes in vitro, IFN-beta leads to a stronger relative upregulation of HLA-G compared to classical MHC class I molecules than stimulation with IFN-gamma. Taken together, monocyte-derived HLA-G mediates the inhibition of autologous CD4 T cell activation and might be involved in immune-regulatory pathways in the pathogenesis of MS. We conclude that some desirable immune-modulatory effects of INF-beta might be accomplished via the upregulation of the immune-tolerogenic molecule HLA-G.

Interferon-beta enhances monocyte and dendritic cell expression of B7-H1 (PD-L1), a strong inhibitor of autologous T-cell activation: relevance for the immune modulatory effect in multiple sclerosis

Antigen-presenting cells (APC) are considered to play a critical role in promoting the (re)activation of potentially autoreactive T cells in multiple sclerosis (MS), an inflammatory demyelinating disorder of the central nervous system (CNS). B7-H1 (PD-L1) is a novel member of the B7 family proteins which exert costimulatory and immune regulatory functions. Here we characterize the expression and functional activity of B7-H1 expressed on monocytes and dendritic cells (DC) of healthy donors and MS patients. B7-H1 is constitutively expressed on monocytes and differentially matured DC, but not on B cells. IFN-beta, the principle immune modulatory agent used for the treatment of MS, strongly enhances B7-H1 expression on monocytes and semi-matured DC, but not B cells, in vitro. Importantly, B7-H1 expressed on APC strongly inhibits autologous CD4 T-cell activation. Neutralization of B7-H1 on monocytes or differentially matured monocyte-derived DC markedly increases the secretion of the pro-inflammatory cytokines, IFN-gamma and IL-2, T-cell proliferation, and the expression of T-cell activation markers. B7-H1 exhibits strong inhibitory effects when expressed on monocytes, immature or semi-mature DC, but less so when expressed on fully matured DC. B7-H1-dependent immune inhibition is in part mediated by CD4/CD25+ regulatory T cells. There is no difference in the baseline expression levels of monocytic B7-H1 between untreated MS patients and healthy donors. However, both groups show a significant concentration-dependent up-regulation of B7-H1 mRNA and protein in response to IFN-beta in vitro. Serial measurements of B7-H1 mRNA in MS patients before and 6 months after initiation of IFN-beta therapy corroborated the relevance of these results in vivo: Nine of nine patients showed a significant increase in B7-H1 mRNA levels after 6 months of IFN-beta therapy (median 1.04 vs. 8.78; p<0.05, two-sided t-test). Accordingly, protein expression of B7-H1 on monocytes was up-regulated after 24 h of IFN-beta application. In summary, B7-H1 expressed on APC acts as a strong inhibitor of autologous CD4 T-cell activation and may thus contribute to the maintenance of peripheral immune tolerance. IFN-beta up-regulates B7-H1 in vitro and in MS patients in vivo and might represent a novel mechanism how IFN-beta acts as a negative modulator on APC T-cell interactions in the periphery.

Express and protect yourself: the potential role of HLA-G on muscle cells and in inflammatory myopathies

Muscle is the site or the target of immunologic injury in several diseases. Whereas under physiologic conditions muscle fibers are negative for major histocompatibility complex (MHC) class I antigens, these are upregulated under pathologic conditions, thus rendering muscle a possible target for the recognition by cytotoxic CD8 T cells. Cultured muscle cells are capable of presenting antigens to CD4 and CD8 T cells, further indicating that muscle fibers in vivo are critically involved in the initiating or perpetuating steps of inflammatory responses. The finding that muscle fibers in autoimmune inflammatory myopathies in vivo and cultured muscle cells in vitro express the nonclassical major histocompatibility complex molecule HLA-G raises several hypothesis concerning its possible pathophysiologic role. We review present knowledge on the functional consequences of muscle-related HLA-G and provide concepts of its relevance under pathologic conditions. We further speculate on the potential therapeutic implications of HLA-G that relate to special approaches such as myoblast transplantation or strategies against inflammatory aggression in general.

Expression of the B7-related molecule ICOSL by human glioma cells in vitro and in vivo

Human glioblastoma is a highly lethal tumor known for its capability of interfering with effective antitumor immune responses. Costimulatory signals are of critical relevance in both the inductive and effector phases of immune responses. Inducible costimulator-ligand (ICOSL), a member of the B7 family of costimulatory molecules related to CD80/CD86, regulates CD4 as well as CD8 T-cell responses via interaction with its receptor, ICOS, on activated T cells. We report the expression of ICOSL by glioma cells in vitro and in vivo. In contrast to CD80 (B7.1) and CD86 (B7.2), ICOSL protein and mRNA was expressed in 7 of 12 glioma cell lines. ICOSL expression is upregulated by the inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), whereas interferon-gamma (IFN-gamma) has no such effect. Further, immunohistochemical analysis of human brain tumors demonstrates the expression of ICOSL in three of four tissue samples. ICOSL expression is functional in that a neutralizing ICOSL antibody (HIL-131) reduces Th1 and Th2 cytokine levels in cocultures of peripheral blood lymphocytes or T-cell subsets (CD4 and CD8) with glioma cells. However, ICOSL gene transfer into glioma cells does not alter their immunogenicity under primary or secondary alloreactive coculture assays.

Expression of the B7-related molecule B7-H1 by glioma cells: a potential mechanism of immune paralysis

Human glioblastoma is a highly lethal tumor that is known for its immune inhibitory capabilities. B7-homologue 1 (B7-H1), a recently identified homologue of B7.1/2 (CD80/86), has been described to exert costimulatory and immune regulatory functions. We investigated the expression and the functional activity of B7-H1 in human glioma cells in vitro and in vivo. Although lacking B7.1/2 (CD80/86), all 12 glioma cell lines constitutively expressed B7-H1 mRNA and protein. Exposure to IFN-gamma strongly enhanced B7-H1 expression. Immunohistochemical analysis of malignant glioma specimens revealed strong B7-H1 expression in all 10 samples examined, whereas no B7-H1 expression could be detected on normal brain tissues. To elucidate the functional significance of glioma cell-related B7-H1 expression, we performed coculture experiments of glioma cells with alloreactive CD4+ and CD8+ T cells. Glioma-related B7-H1 was identified as a strong inhibitor of CD4+ as well as CD8+ T-cell activation as assessed by increased cytokine production (IFN-gamma, interleukin-2, and interleukin-10) and expression levels of the T-cell activation marker (CD69) in the presence of a neutralizing antibody against B7-H1 (mAb 5H1). B7-H1 expression may thus significantly influence the outcome of T-cell tumor cell interactions and represents a novel mechanism by which glioma cells evade immune recognition and destruction.

Hide-and-seek in the brain: a role for HLA-G mediating immune privilege for glioma cells

This review summarizes the current knowledge on the expression and functional role of HLA-G in normal CNS cells and brain tumor cells in vitro and in vivo. The CNS has classically been viewed as an immune-privileged organ. Here we discuss some of the particularities of anti-tumoral responses within this compartment. Special emphasis is dedicated to the possible role of the non-classical MHC molecule HLA-G as an alternative mechanism of immune escape. We review the mechanisms how glioma cell-derived HLA-G may paralyze the immune system and which cellular subsets of the immune system are affected. Possible therapeutic implications derived from these observations include the targeting of HLA-G expression within the framework of inducing glioma-specific immunity.

Human muscle cells express a B7-related molecule, B7-H1, with strong negative immune regulatory potential: a novel mechanism of counterbalancing the immune attack in idiopathic inflammatory myopathies

B7-H1 is a novel B7 family protein attributed to costimulatory and immune regulatory functions. Here we report that human myoblasts cultured from control subjects and patients with inflammatory myopathies as well as TE671 muscle rhabdomyosarcoma cells express high levels of B7-H1 after stimulation with the inflammatory cytokine IFN-gamma. Coculture experiments of MHC class I/II-positive myoblasts with CD4 and CD8 T cells in the presence of antigen demonstrated the functional consequences of muscle-related B7-H1 expression: production of inflammatory cytokines, IFN-gamma and IL-2, by CD4 as well CD8 T cells was markedly enhanced in the presence of a neutralizing anti-B7-H1 antibody. This observation was paralleled by an augmented expression of the T cell activation markers CD25, ICOS, and CD69, thus showing B7-H1-mediated inhibition of T cell activation. Further, we investigated 23 muscle biopsy specimens from patients with polymyositis (PM), inclusion body myositis (IBM), dermatomyositis (DM), and nonmyopathic controls for B7-H1 expression by immunohistochemistry: B7-H1 was expressed in PM, IBM, and DM specimens but not in noninflammatory and nonmyopathic controls. Staining was predominantly localized to areas of strong inflammation and to muscle cells as well as mononuclear cells. These data highlight the immune regulatory properties of muscle cells and suggest that B7-H1 expression represents an inhibitory mechanism induced upon inflammatory stimuli and aimed at protecting muscle fibers from immune aggression.

The CD28 related molecule ICOS: T cell modulation in the presence and absence of B7.1/2 and regulational expression in multiple sclerosis

Costimulatory signals play a key role in regulating T cell activation and are believed to have decisive influence in the inciting and perpetuating cellular effector mechanisms in autoimmune diseases such as multiple sclerosis (MS). Inducible costimulator protein (ICOS), a recently identified member of the CD28-family, presumably affects the differentiation of Th1/Th2 cells after primary activation and modulates the immune response of effector/memory T cells. This study examines the expression and functional role of ICOS costimulation in healthy donors and patients with MS. After nonspecific or antigen-specific stimulation, ICOS is preferentially expressed on CD4 Th2-T cells. ICOS-costimulation affects the production of Th1 and Th2 cytokines both in the absence and presence of B7/CD28 costimulation, thus suggesting that ICOS costimulation can modulate cytokine secretion also in a CD28-independent manner. Levels of constitutive and inducible ICOS expression on human T cell subsets from peripheral blood were quantified in healthy donors and patients with MS. Constitutive expression of ICOS on T cells varies between 0.1% and 42.3%. There were no significant differences between both groups in the baseline expression or inducibility of ICOS on CD4 or CD8 T cells. ICOS expression could be demonstrated on CSF T lymphocytes in patients with acute MS relapses but was not elevated compared with peripheral blood. In essence we show that ICOS is upregulated on human T cells after stimulation and can modulate both Th1 and Th2 cytokine production in the absence and presence of B7-costimulation. In MS patients we demonstrate the functionality of the ICOS costimulatory pathway. Potential implications of ICOSL/ICOS interactions for MS immunopathogenesis are discussed.

Muscle fibres and cultured muscle cells express the B7.1/2-related inducible co-stimulatory molecule, ICOSL: implications for the pathogenesis of inflammatory myopathies

Inducible co-stimulator ligand (ICOSL), a member of the B7 family of co-stimulatory molecules related to B7.1/2, regulates CD4 as well as CD8 T-cell responses via interaction with its receptor ICOS on activated T cells. Here we examined the expression and the functional relevance of ICOSL in human muscle cells in vivo and in vitro. We investigated 25 muscle biopsy specimens from patients with polymyositis, dermatomyositis, inclusion body myositis, Duchenne muscular dystrophy and non-myopathic controls for ICOSL expression by immunohistochemistry. Normal muscle fibres constitutively express low levels of ICOSL. However, ICOSL expression is markedly increased in muscle fibres in inflammatory myopathies. Cell surface staining was most prominent in the contact areas between muscle fibres and inflammatory cells, which in turn show expression of ICOS as a marker of T-cell activation. Muscle endothelial cells show constitutive expression of ICOSL under normal and pathological conditions. We also detected mRNA and cell surface protein expression of ICOSL on myoblasts cultured from control subjects and patients as well as in TE671 muscle rhabdomyosarcoma cells. ICOSL expression was upregulated by tumour necrosis factor-alpha (TNF-alpha), whereas interferon-gamma (IFN-gamma) had no such effect. Co-culture experiments of major histocompatibility complex (MHC) class II-positive myoblasts with CD4 T cells together with superantigen demonstrated that the expression of muscle-related ICOSL has functional consequences: the production of Th1 (IFN-gamma) and Th2 cytokines [interleukin (IL)-4 and IL-10] by CD4 T cells was markedly reduced in the presence of a neutralizing anti-ICOSL monoclonal antibody (mAb HIL-131), thus showing the importance of ICOSL co-stimulation for T-cell activation. Taken together, our results demonstrate that human muscle cells express ICOSL, a functional co-stimulatory molecule distinct from B7.1 and B7.2. ICOSL-ICOS interactions may play an important role in inflammatory myopathies, providing further evidence for the antigen-presenting capacity of muscle cells.

The non-classical MHC molecule HLA-G protects human muscle cells from immune-mediated lysis: implications for myoblast transplantation and gene therapy

HLA-G is a non-classical MHC class I molecule with highly limited tissue distribution which has been attributed chiefly immune-regulatory functions. We previously have reported that HLA-G is expressed in inflamed muscle in vivo and by cultured myoblasts in vitro. Here, we used the in vitro models of human myoblasts or TE671 muscle rhabdomyosarcoma cells to characterize the functional role of HLA-G for muscle immune cell interactions. Gene transfer of the two major isoforms of HLA-G (transmembranous HLA-G1 and soluble HLA-G5) into TE671 rendered these cells resistant to alloreactive lysis by direct inhibition of natural killer (NK) cells, and CD4 and CD8 T cells. Further, HLA-G reduced alloproliferation, interfered with effective priming of antigen-specific cytotoxic T cells and reduced antigen-specific alloreactive lysis. HLA-G pre-induced on cultured myoblasts inhibited lysis by alloreactive peripheral blood mononuclear cells. This protection was reversed by a neutralizing HLA-G antibody. Interestingly, a few HLA-G-positive cells within a population of HLA-G-negative muscle target cells conveyed significant inhibitory effects on alloreactive lysis. Our results reveal further insights into the immunobiology of muscle and suggest that ectopic expression of HLA-G may promote the survival of transplanted myoblasts in the future treatment of hereditary muscle diseases. Further, HLA-G could represent a novel self-derived anti-inflammatory principle applicable in strategies against inflammatory aggression.

A functional role of HLA-G expression in human gliomas: an alternative strategy of immune escape

HLA-G is a nonclassical MHC molecule with highly limited tissue distribution that has been attributed chiefly immune regulatory functions. Glioblastoma is paradigmatic for the capability of human cancers to paralyze the immune system. To delineate the potential role of HLA-G in glioblastoma immunobiology, expression patterns and functional relevance of this MHC class Ib molecule were investigated in glioma cells and brain tissues. HLA-G mRNA expression was detected in six of 12 glioma cell lines in the absence of IFN-gamma and in 10 of 12 cell lines in the presence of IFN-gamma. HLA-G protein was detected in four of 12 cell lines in the absence of IFN-gamma and in eight of 12 cell lines in the presence of IFN-gamma. Immunohistochemical analysis of human brain tumors revealed expression of HLA-G in four of five tissue samples. Functional studies on the role of HLA-G in glioma cells were conducted with alloreactive PBMCs, NK cells, and T cell subpopulations. Expression of membrane-bound HLA-G1 and soluble HLA-G5 inhibited alloreactive and Ag-specific immune responses. Gene transfer of HLA-G1 or HLA-G5 into HLA-G-negative glioma cells (U87MG) rendered cells highly resistant to direct alloreactive lysis, inhibited the alloproliferative response, and prevented efficient priming of cytotoxic T cells. The inhibitory effects of HLA-G were directed against CD8 and CD4 T cells, but appeared to be NK cell independent. Interestingly, few HLA-G-positive cells within a population of HLA-G-negative tumor cells exerted significant immune inhibitory effects. We conclude that the aberrant expression of HLA-G may contribute to immune escape in human glioblastoma.