Transforming growth factor-β1 suppresses autoantigen-induced expression of pro-inflammatory cytokines but not of interleukin-10 in multiple sclerosis and myasthenia gravis

Multiple sclerosis (MS) is associated with high levels of circulating T lymphocytes that respond to the myelin antigens myelin basic protein (MBP) and proteolipid protein (PLP) by producing various cytokines including interferon-γ (IFN-γ) that makes MS worse and transforming growth factor-β (TGF-β), an endogenously produced immunosuppressant that might act beneficially. To further define the role of TGF-β in MS, we examined the effects of recombinant TGF-β1 (rTGF-β1) on autoantigen-mediated regulation of cytokines in MS and myasthenia gravis (MG). Blood mononuclear cells (MNC) were cultivated with or without rTGF-β1, and with or without autoantigen or the recall antigen PPD. MNC expressing cytokine mRNA were detected after in situ hybridization with radiolabeled cDNA oligonucleotide probes. Femtogram concentrations of rTGF-β1 suppressed MBP-, PLP- and PPD-induced upregulation of IFN-γ, IL-4, IL-6, tumor necrosis factor-α (TNF-α), TNF-α and perforin in MS, and acetylcholine receptor (AChR)-induced augmentation of these pro-inflammatory cytokines in MG, but had no effects on autoantigen- or PPD-induced expression of IL-10 or TGF-β itself. rTGF-β1 also suppressed numbers of myelin antigen-reactive IFN-γ- and IL-4-secreting cells in MS and AChR-reactive IFN-γ and IL-4 secreting cells in MG. The selective suppressive effects of TGF-β1 on autoantigen-induced upregulation of pro-inflammatory cytokines makes TGF-β1 attractive as a treatment alternative in MS and MG.     

Increased transforming growth factor-β, interleukin-4, and interferon-γ in multiple sclerosis

The inflammatory nature of multiple sclerosis (MS) implicates the participation of immunoregulatory cytokines, including the T-helper type 1 (Th1) cell–associated interferon-σ (IFN-σ), the Th2 cell–related interleukin-4 (IL-4), and the immune response–downregulating cytokine transforming growth factor-β (TGF-β), but proof for their involvement in MS has been lacking. By adopting in situ hybridization with complementary DNA oligonucleotide probes for human IFN- IL-4, and TGF-β, the expression of mRNA for these cytokines was detected in mononuclear cells (MNC) from blood and cerebrospinal fluids. Strongly elevated levels of MNC expressing all three cytokines were found in peripheral blood and at even higher frequencies in cerebrospinal fluid from untreated patients with MS and optic neuritis, i.e., a common first manifestation of MS, compared with patients with other neurological diseases and healthy subjects. In MS and optic neuritis, IL-4 mRNA expressing cells predominated, followed by TGF-β– and IFN-σ–positive cells. Control patients with myasthenia gravis had similarly elevated levels of IFN-σ and TGF-β mRNA expressing blood MNC but lower numbers of IL-4–positive cells. No or slight disability of MS was associated with high levels of TGF-β mRNA expressing cells, while MS patients with moderate or severe disability had high levels of IFN-σ–positive cells. IFN-σ and TGF-β may have opposing effects in MS, and treatments inhibiting IFN-σ and/or promoting TGF-β might ameliorate MS.     

Autoantigen-induced IL-13 mRNA expression is increased in blood mononuclear cells in myasthenia gravis and multiple sclerosis

Evidence has been presented for the involvement of immune mechanisms in the pathogenesis of myasthenia gravis (MG) and multiple sclerosis (MS). The production of autoantibodies in both diseases is regulated by T-cells by means of cytokines. Interleukin-13 (IL-13) is mainly produced by T-helper type 2 cells and induces B-cell proliferation and antibody class switch. The role of IL-13 in MG and MS is not known. We employed in situ hybridization with synthetic radiolabelled oligonucleotide probes to detect and enumerate blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) expressing IL-13 mRNA from patients with MG, MS, optic neuritis (ON), other inflammatory neurological diseases (OIND) and healthy controls. MG is associated with elevated levels of acetylcholine receptor (AChR) reactive IL-13 mRNA expressing blood MNC compared to control patients. In MS, numbers of MBP-reactive IL-13 mRNA expressing MNC were higher compared to cultures without antigen stimulation. The levels of MBP-reactive IL-13 mRNA positive MNC were higher in MS compared to MG, but not other controls. There were no differences in spontaneous IL-13 mRNA expressing blood MNC numbers between MG, MS, ON and control patients. The data suggest the involvement of IL-13 in both MG and MS.     

Suppression of experimental autoimmune myasthenia gravis and experimental allergic encephalomyelitis by oral administration of acetylcholine receptor and myelin basic protein: double tolerance

Oral administration of acetylcholine receptor (AChR) or myelin basic protein (MBP) to Lewis rat prior to immunization with AChR or MBP and complete Freund's adjuvant (CFA) has previously been shown to prevent or delay the onset of experimental autoimmune myasthenia gravis (EAMG) or experimental allergic encephalomyelitis (EAE), which represent animal models of myasthenia gravis and multiple sclerosis, respectively. Here we show that Lewis rats immunized with AChR + MBP + CFA developed both signs of muscular weakness seen in EAMG and paresis characteristic for EAE. This disease was associated with high levels of anti-AChR and anti-MBP antibody secreting cells and of AChR- and MBP-reactive INF-γ secreting Th1-like cells in lymph nodes. The diseased rats also showed upregulation of AChR- and MBP-induced mRNA expression of IFN-γ in lymph node cells. Oral tolerization with AChR and MBP in combination prior to immunization with AChR + MBP + CFA alleviated clinical disease as well as AChR- and MBP-specific B cell responses and autoantigen-induced IFN-γ secretion and production, but upregulated antigen-induced TGF-β mRNA expression in lymph node cells. The results implicate that oral tolerization simultaneously to more than one autoimmune disease-related autoantigen is feasible, and that suppression of autoantigen-induced IFN-γ and augmentation of TGF-β are pivotal in tolerance induction.     

Multiple sclerosis: myelin basic protein induced mRNA expression of proinflammatory cytokines in mononuclear cells is suppressed by interferon-β 1b in vitro

Beta-interferon (IFN-β) is a promising treatment in multiple sclerosis (MS), reducing the exacerbation rate and MRI lesion burden, as well as the disease progression in relapsing-remitting MS. IFN-β was originally defined by its antiviral effects, but the interest has recently been focused on its immunomodulatory properties. Myelin basic protein (MBP) is one of several autoantigens considered to be the target for autoaggressive immune responses, which eventually might lead to the development of MS. To study in-vitro effects of IFN-β1b on MBP induced cytokine expression, mRNA for the Th1 cytokines IFN-γ and TNF-α, the Th2 related IL-4 and IL-6, the cytolytic perforin and the immune response downregulating TGF-β was measured with in situ hybridization after culture of blood mononuclear cells (MNC) in the presence and absence of MBP. Numbers of cells expressing IFN-γ, TNF-α, perforin and IL-4 mRNA were significantly suppressed after culture with 10 U/ml IFN-β1b. No such effect was seen on MBP induced IL-6 or TGF-β mRNA expression. These observations suggest that one of the major effects of IFN-β1b is the induction of a shift in the cytokine mRNA profile towards a more immunosuppressive pattern. In parallel in vitro tests, the control substance dexametasone (40 μg/ml) reduced the numbers of cells expressing mRNA for all cytokines under study with the exception of TGF-β, to an extent equal to or even more pronounced than IFN-β1b.     

Frequency of T cells specific for myelin basic protein and myelin proteolipid protein in blood and cerebrospinal fluid in multiple sclerosis

T cell sensitization to two myelin components, myelin basic protein (MBP) and myelin proteolipid protein (PLP), may be important to the pathogenesis of multiple sclerosis (MS). Using the limiting dilution assay, we demonstrated that the blood of MS patients had an increased frequency of MBP-reactive T cells compared with normal subjects and patients with other neurological diseases (OND) and rheumatoid arthritis. There was no difference in T cell frequency to a synthetic peptide, PLP139-151, or Herpes simplex virus. Within cerebrospinal fluid (CSF), 37% of IL-2/IL-4-reactive T cell isolates from MS patients responded either to MBP or PLP139-151 while only 5% of similar isolates from OND patients responded to these myelin antigens. The mean relative frequency of MBP-reactive T cells within CSF from MS patients was significantly higher than that of OND patients (22 x 10(-5) cells versus 1 x 10(-5) cells) and was similar to that of MBP reactive T cells within the central nervous system of rats with experimental autoimmune encephalomyelitis. These results lend new support to the hypothesis that myelin-reactive T cells mediate disease in MS.     

多发性硬化症髓鞘素组分特异性抗体分泌细胞

本文用酶联免疫斑点法（Ｅｌｉｓｐｏｔ）检测了２３例临床确诊多发性硬化症（ＭＳ）和１２例无菌性脑膜炎（ＡＭ）患者外周血（ＰＢ）和脑脊液（ＣＳＦ）中髓鞘素碱性蛋白（ＭＢＰ）、髓鞘素结合糖蛋白（ＭＡＧ）和含脂质蛋白（ＰＬＰ）特异性ＩｇＧ抗体分泌细胞。两组患者ＣＳＦ中该３种抗体分泌细胞均呈明显增多趋势，ＭＳ组尤著，但两组ＰＢ中该类细胞数均很少。指示对髓鞘素组分的Ｂ细胞免疫应答主要局限于与中枢神经系统（ＣＮ     

Interleukin-17 mRNA expression in blood and CSF mononuclear cells is augmented in multiple sclerosis.

Myelin-directed autoimmunity is considered to play a key role in the pathogenesis of multiple sclerosis (MS). Increased production of both pro- and anti-inflammatory cytokines is a common finding in MS. Interleukin-17 (IL-17) is a recently described cytokine produced in humans almost exclusively by activated memory T cells, which can induce the production of proinflammatory cytokines and chemokines from parenchymal cells and macrophages. In situ hybridisation with synthetic oligonucleotide probes was adopted to detect and enumerate IL-17 mRNA expressing mononuclear cells (MNC) in blood and cerebrospinal fluid (CSF) from patients with MS and control individuals. Numbers of IL-17 mRNA expressing blood MNC were higher in patients with MS and acute aseptic meningoencephalitis (AM) compared to healthy individuals. Higher numbers of IL-17 mRNA expressing blood MNC were detected in MS patients examined during clinical exacerbation compared to remission. Patients with MS had higher numbers of IL-17 mRNA expressing MNC in CSF compared to blood. This increase in numbers of IL-17 mRNA expressing MNC in CSF was not observed in patients with AM. Our results thus demonstrate increased numbers of IL-17 mRNA expressing MNC in MS with higher numbers in CSF than blood, and with the highest numbers in blood during clinical exacerbations.     

Clues to the immunopathogenesis of multiple sclerosis by investigating untreated patients during the very early stage of disease

Plethora of abnormalities of the immune system has been described in multiple sclerosis (MS). They include a number of myelin antigens (e. g. MBP, MOG, PLP, MAG), the presence of reactive T cells in blood and, further enriched, in the cerebrospinal fluid (CSF), large numbers of B cells in the CSF secreting antibodies of multiple but unknown specificities, an increase of mononuclear cells (MNC) expressing and secreting both pro- and anti-inflammatory cytokines, including Th1 cytokines interferon-gamma (IFN-γ) and interleukin (IL)-6, the Th2 related IL-4 and IL-10, and the Th3-driven TGF-β, elevated numbers of MNC in both blood and CSF expressing a spectrum of metalloproteinases and their inhibitors, as well as many other aberrations. However, no consistent patterns have emerged that relate any of these findings to clinical variables such as exacerbations, during of disease, disability, or lesions in the central nervous system (CNS) detected at magnetic resonance imaging. In order to elucidate the relevance of these immunological abnormalities in the pathogenesis of MS, my colleagues and I studied patients with acute monosymptomatic optic neuritis (ON) and compared them with patients with clinically definite MS (CDMS). The patients have not been treated and have not received corticosteroids or interferon-β. When comparing these two groups, we were unable to identify any differences in any of the variables mentioned. Thus, very early MS, as represented by ON, shows the same full-blown pattern of immunological abnormalities seen in CDMS. Furthermore, a complete epitope spread affecting MBP, MOG, PLP, MAG and other myelin components is already present in ON. Whether any of these alterations play a pathogenetic role is still unsettled.     

亚低温治疗对实验性脑出血大鼠死亡率及脑组织钙含量的影响

目的本研究观察３２℃亚低温对实验性脑出血大鼠２４ｈ内死亡率和脑组织钙含量的影响。方法１３４只大鼠分成两部分：（１）６８只大鼠用于死亡率观察;（２）６６只大鼠用于脑组织钙含量测定。每一部分分成假手术对照组、常温脑出血组及亚低温脑出血组。结果常温组２４ｈ内死亡率为３６．６７％,亚低温组为４．５５％;脑组织钙含量常温组较对照组和亚低温组为高。结论亚低温治疗能显著减少实验性脑出血大鼠２４ｈ内死亡率,减少脑出血后脑组织钙含量。     

Multiple sclerosis: occurrence of myelin basic protein peptide-reactive T cells in healthy family members

Genetic factors influence the susceptibility to multiple sclerosis (MS). This disease is accompanied by augmented T cell responses to CNS myelin components such as myelin basic protein. To evaluate the familial occurrence of such T cell autoreactivity, we have studied 12 MS families including 37 healthy first-degree relatives for occurrence of numbers of interferon-gamma (IFN-γ) secreting cells among blood mononuclear after culture in presence of myelin basic protein (MBP), eight synthetic MBP peptides and the control antigen acetylcholine receptor (AChR). There were no differences between MS patients and healthy family members regarding frequencies of autoreactive T cells recognizing MBP, the eight different MBP peptides or AChR. None of the MBP peptides predominated as T cell antigen among the MS patients or their unaffected family members. In some families the highest number of MBP peptide reactive T cells were found among unaffected family members. No correlation was observed between numbers of MBP or MBP peptide reactive T cells in various subjects and their HLA-DR-DQ phenotypes. In conclusion, this study has revealed the presence of MBP and MBP peptide reactive T cells of similar frequencies in MS patients and their healthy family members.     

重症肌无力患者对糖皮质激素的敏感性与糖皮质激素受体的关系

目的　了解重症肌无力(MG)患者对糖皮质激素(GC)敏感性与糖皮质激素受体(GR)的关系。 方法　观察10例MG患者及10名健康对照。采用 3　H-地塞米松( 3　H-DEX)放射配体法测定外周血单个核细胞(PBMC)GR。分别用植物血凝素(PHA)、髓鞘碱性蛋白(MBP)、乙酰胆碱受体(AChR)刺激PBMC， 3　H-TdR掺入法检测体外淋巴细胞增殖反应，地塞米松(DEX)抑制淋巴细胞增殖反应。 结果　正常对照及MG患者PBMC对PHA及MBP刺激的增殖反应差别不显著(P>,0 .05)。而MG患者PBMC对AChR的反应明显高于正常对照者(P<,0 .01)。DEX对MG患者PBMC特异性增殖反应的抑制率为42 .14%, 而对正常对照PBMC的增殖反应的抑制率为21 .62％，两组间有很显著区别(P<,0 .01)。GR数与DEX抑制率间有很良好的相关关系(r=0 .943, P<,0 .01)。 结论　MG PBMC GR数与体外DEX对PBMC 特异性增殖反应的抑制效应有良好的一致性。DEX对抗原特异性淋巴细胞增殖反应的抑制性可作为了解MG患者对GC敏感性的一项指标。     

Muscle antibodies in the cerebrospinal fluid from patients with myasthenia gravis

IgG antibodies to nicotinic acetylcholine receptor (AChR) and to a muscle antigen extracted by citric acid, were quantified in serum and cerebrospinal fluid (CSF) from 28 patients with myasthenia gravis, and the serum:CSF ratios compared with those of total IgG. Agarose-electrophoresis and calculations of the IgG index and Tourtellotte's formula were performed. No evidence of intrathecal antibody synthesis was demonstrated. Compared to the total IgG concentrations in serum and CSF, the CSF concentrations of IgG AChR antibodies were lower than expected.     

Acetylcholine receptors in human thymic myoid cells in situ: an immunohistological study

Myoid cells were studied by double immunofluorescence in sections of thymus from 47 patients with myasthenia gravis and 15 control subjects, using polyclonal sheep anti-troponin T and monoclonal antibodies to troponin I, striated muscle myosin, and acetylcholine receptor (AChR). The myoid cells were rare and located mainly in the medulla, and most were clearly positive for AChR; labeling was similar with four individual monoclonal antibodies specific for extrajunctional AChR and five that also recognize endplate AChR. They were mostly keratin-positive and consistently HLA-DR-negative. In the myasthenia gravis samples, the myoid cells were similar but largely confined to medullary epithelial areas; AChR labeling was slightly weaker, but otherwise they did not differ noticeably from those of control subjects. A preliminary finding was of even rarer AChR-positive/HLA-DR-positive antigen-presenting (possibly) cells seen in 9 of 9 myasthenia gravis samples and in none of 9 control samples. Although myoid-cell AChR appears antigenically similar to extrajunctional muscle AChR, and must therefore express the epitopes that myasthenics' antibodies recognize, these cells do not appear to be foci of immunological stimulation in myasthenia gravis.     

Abundant extracellular myelin in the meninges of patients with multiple sclerosis

Background:  In multiple sclerosis (MS) myelin debris has been observed within MS lesions, in cerebrospinal fluid and cervical lymph nodes, but the route of myelin transport out of the brain is unknown. Drainage of interstitial fluid from the brain parenchyma involves the perivascular spaces and leptomeninges, but the presence of myelin debris in these compartments has not been described. Aims: To determine whether myelin products are present in the meninges and perivascular spaces of MS patients. Methods: Formalin-fixed brain tissue containing meninges from 29 MS patients, 9 non-neurological controls, 6 Alzheimer's disease, 5 stroke, 5 meningitis and 7 leucodystrophy patients was investigated, and immunohistochemically stained for several myelin proteins [proteolipid protein (PLP), myelin basic protein (MBP), myelin oligodendrocyte glycoprotein (MOG) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase)]. On brain material from MS patients and (non)neurological controls, PLP immunostaining was used to systematically investigate the presence of myelin debris in the meninges, using a semiquantitative scale. Results: Extensive extracellular presence of myelin particles, positive for PLP, MBP, MOG and CNPase in the leptomeninges of MS patients, was observed. Myelin particles were also observed in perivascular spaces of MS patients. Immunohistochemical double-labelling for macrophage and dendritic cell markers and PLP confirmed that the vast majority of myelin particles were located extracellularly. Extracellular myelin particles were virtually absent in meningeal tissue of non-neurological controls, Alzheimer's disease, stroke, meningitis and leucodystrophy cases. Conclusions: In MS leptomeninges and perivascular spaces, abundant extracellular myelin can be found, whereas this is not the case for controls and other neurological disease. This may be relevant for understanding sustained immunogenicity or, alternatively, tolerogenicity in MS.     

High numbers of perforin mRNA expressing CSF cells in multiple sclerosis patients with gadolinium-enhancing brain MRI lesions

Enhanced expression of pro- and anti-inflammatory cytokines is a common finding in MS, but attempts to correlate cytokine expression with disease activity have produced conflicting results. In this paper, gadolinium-(Gd-)enhancing lesions on brain MRI were used as markers for active inflammation in patients with MS not treated with any immunomodulatory drugs. In parallel, in situ hybridization was used to detect blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) expressing cytokine mRNA. An association was observed between numbers of perforin mRNA expressing CSF MNC and numbers of Gd-enhancing brain MRI lesions. Perforin mRNA expressing CSF MNC were not detected in any of the patients lacking active lesions on brain MRI. The expression of tumor necrosis factor-alpha, interleukin-10 (IL-10) and IL-12 mRNA in CSF MNC did not differ between MS patients with and without active MRI lesions. Based on the present finding, a role for perforin in the disruption of the blood-brain barrier in MS can be hypothesized.     

The B-cell repertoire in myasthenia gravis includes all four acetylcholine receptor subunits

By enumerating cells secreting IgG antibodies of particular specificities using an enzyme-linked immunospot (ELISPOT) assay, the B-cell responses to Torpedo acetylcholine receptor (AChR) and its α-, β-, γ- and δ-subunits in peripheral blood from patients with myasthenia gravis (MG), and controls with other neurological diseases (OND) as well as healthy subjects were determined. Compared to controls, the patients with MG had elevated numbers of B cells secreting antibodies against AChR and its α-, β-, γ- and δ-subunits in peripheral blood in parallel. The mean numbers of anti-AChR antibody secreting cells were about 17 per 10⁵ blood MNC, and for the subunits 10 to 15 in MG patients, compared to between 0.8 and 1.9 per 10⁵ blood MNC in OND patients, and 0.1 to 0.3 in healthy controls. Such B cells detected in controls probably represent naturally occurring B cells responded to AChR and its subunits. The finding that most (60%) MG patients had B cells predominantly recognizing the α-subunit may be an indirect argument for the existence of a main immunogenic region (MIR). In the remaining 40% of patients with MG the predominant B-cell responses were directed to β-, γ- or δ-subunit. The data suggest that all four AChR subunits may function as strong immunogens in MG, though the α-subunit may be the major immune target in a substantial proportion of MG patients.     

Neuromuscular junction autoimmune disease: muscle specific kinase antibodies and treatments for myasthenia gravis

PURPOSE OF REVIEW: Some of the 20% of myasthenia gravis patients who do not have antibodies to acetylcholine receptors (AChRs) have antibodies to muscle specific kinase (MuSK), but a full understanding of their frequency, the associated clinical phenotype and the mechanisms of action of the antibodies has not yet been achieved. Moreover, some patients do not respond well to conventional corticosteroid therapy. Here we review recent clinical and experimental studies on MuSK antibody associated myasthenia gravis, and summarize the results of newer treatments for myasthenia gravis. RECENT FINDINGS: MuSK antibodies are found in a variable proportion of AChR antibody negative myasthenia gravis patients who are often, but not exclusively, young adult females, with bulbar, neck, or respiratory muscle weakness. The thymus histology is normal or only very mildly abnormal. Surprisingly, limb or intercostal muscle biopsies exhibit no reduction in AChR numbers or complement deposition. However, patients without AChR or MuSK antibodies appear to be similar to those with AChR antibodies and may have low-affinity AChR antibodies. A variety of treatments, often intended to enable corticosteroid doses to be reduced, have been used in all types of myasthenia gravis with some success, but they have not been subjected to randomized clinical trials. SUMMARY: MuSK antibodies define a form of myasthenia gravis that can be difficult to diagnose, can be life threatening and may require additional treatments. An improved AChR antibody assay may be helpful in patients without AChR or MuSK antibodies. Clinical trials of drugs in other neuroimmunological diseases may help to guide the treatment of myasthenia gravis.     

Biased expression of T cell receptor genes characterizes activated T cells in multiple sclerosis cerebrospinal fluid

To better characterize the inflammatory response that occurs in the nervous system in multiple sclerosis (MS), T-cell receptor (TCR) gene expression was quantified from cerebrospinal fluid (CSF) cells of 21 patients with active disease. Unstimulated CSF cells expressed each of 22 different TCR beta chain variable region (Vβ) gene families in proportion to their expression in simultaneously sampled peripheral blood. When CSF cells from individuals with MS were expanded by in vitro culture in T-cell growth factor/interleukin 2 and 4-containing medium (TCGF/IL2/IL4), restricted numbers of Vβ genes were expressed. In many subjects, expanded CSF cells expressed predominantly Vβ2. In contrast to CSF, expansion of corresponding peripheral blood mononuclear cells (PBMC) in TCGF/IL2/IL4 resulted in persistent expression of an Vβ gene families. Within individuals, different Vβ genes were overexpressed by PBMC compared with CSF cells. No effect of the HLA haplotype of the individual on CSF Vβ gene expression was observed. Expanded CSF cells retained their capacity to respond to mitogen stimulation, but the proliferative response to myelin basic protein (MBP) was not enhanced. Finally, freshly obtained CSF cells stimulated directly with MBP also expressed a limited number of Vβ genes, although these were generally different from patterns observed following stimulation with TCGF/IL2/IL4. Thus, restricted populations of T cells capable of responding to TCGF/IL2/IL4, presumably reflecting in vivo activated cells, are compartmentalized in the nervous system in MS. © 1996 Wiley-Liss, Inc.     

Effect of sera from AChR-antibody negative myasthenia gravis patients on AChR and MuSK in cell cultures

A proportion of patients with myasthenia gravis (MG) do not have antibodies to the acetylcholine receptor (AChR). Some of these patients have antibodies to muscle specific kinase (MuSK), whereas others have neither antibody (seronegative MG, SNMG). Both MuSK antibody positive MG (MuSK-MG) and SNMG are antibody-mediated diseases but how they cause neuromuscular junction failure is not clear. One possibility is that they reduce the clustering and expression of AChRs. We looked at the effects of MuSK-MG and SNMG sera/IgG on surface AChR distribution and expression, and AChR subunit and MuSK mRNA by quantitative RT-PCR, in TE671 and C2C12 myotubes. In TE671 cells MuSK-MG sera reduced AChR expression by about 20%, but had no effect on AChR subunit or MuSK mRNA expression. In C2C12 myotubes, MuSK-MG sera caused a reduction in the number of agrin-induced clusters, but the clusters became larger and there was no significant effect on total surface AChR numbers or AChR subunit or MuSK mRNA. By contrast, SNMG sera not only reduced AChR numbers by about 20% in TE671 cells, but modestly upregulated AChR gamma subunit expression in TE671 cells and both AChR gamma subunit and MuSK expression in C2C12 myotubes. Thus, although these results have, disappointingly, demonstrated little effect of MuSK antibodies on AChR expression, they do imply that SNMG antibodies act on AChR-associated pathways.