T cell responses to human recombinant acetylcholine receptor-alpha subunit in myasthenia gravis and controls

Autoimmune Thyroiditis and Myasthenia Gravis

Autoimmune diseases (AIDs) are the result of specific immune responses directed against structures of the self. In normal conditions, the molecules recognized as "self" are tolerated by immune system, but when the self-tolerance is lost, the immune system could react against molecules from the body, causing the loss of self-tolerance, and subsequently the onset of AID that differs for organ target and etiology. Autoimmune thyroid disease (ATD) is caused by the development of autoimmunity against thyroid antigens and comprises Hashimoto's thyroiditis and Graves disease. They are frequently associated with other organ or non-organ specific AIDs, such as myasthenia gravis (MG). In fact, ATD seems to be the most associated pathology to MG. The etiology of both diseases is multifactorial and it is due to genetic and environmental factors, and each of them has specific characteristics. The two pathologies show many commonalities, such as the organ-specificity with a clear pathogenic effect of antibodies, the pathological mechanisms, such as deregulation of the immune system and the implication of the genetic predisposition. They also show some differences, such as the mode of action of the antibodies and therapies. In this review that focuses on ATD and MG, the common features and the differences between the two diseases are discussed.

Vaccines against myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies to nicotinic acetylcholine receptor (AChR) interfering with the neuromuscular transmission. Experimental autoimmune MG serves as an excellent animal model to study possible therapeutic modalities for MG. This review will focus on the different ways to turn off the autoimmune response to AChR, which results in suppression of myasthenia. This paper will describe the use of fragments or peptides derived from the AChR, antigen-presenting cells and anti-T cell receptor antibodies, and will discuss the underlying mechanisms of action. Finally, the authors propose new promising therapeutic prospects, including treatment based on the modulation of regulatory T cells, which have recently been found to be functionally defective in MG patients.

Myasthenia gravis patients, but not healthy subjects, recognize epitopes that are unique to the epsilon-subunit of the acetylcholine receptor

Myasthenia gravis (MG) is an autoimmune disease characterized by deficits in neuromuscular transmission due to antibody-mediated damage of the acetylcholine receptor (AChR). We examined the in vitro immune response of peripheral blood mononuclear cells isolated from MG patients (n=38) and healthy nonmyasthenic subjects (n=31) to epitopes on the alpha-, epsilon-, and gamma-chains of the AChR. The epsilon- and gamma-epitopes tested represent regions with little sequence homology to the alpha-chain, and little sequence homology between the epsilon- and gamma-chains. No differences were observed in the immune response of MG patients and healthy subjects to any of the alpha-chain epitopes tested. Serial studies of the immune response to the alpha-peptides suggest that epitope spread does occur over time. Cells from MG patients were stimulated by the epsilon- and gamma-chain peptides, although the response was weaker than that to the alpha-peptides. Cells from healthy subjects showed reactivity to gamma-chain peptides only; none of the healthy subjects responded to the epsilon-chain peptides tested. Differences between the epsilon- and gamma-chains may be important in the development of MG, because only MG patients respond to epitopes that are unique to the epsilon-subunit.

Interleukin-12 enhances clinical experimental autoimmune myasthenia gravis in susceptible but not resistant mice

Experimental autoimmune myasthenia gravis (EAMG) is induced by antibodies against the nicotinic acetylcholine receptor (AChR). Studies indicate a role for interferon-gamma (IFN-gamma) in EAMG. We examined the effect of IL-12, a major inducer of IFN-gamma production, on EAMG in C57BL/6 mice. Five doses of IL-12 accelerated and enhanced clinical disease in AChR-immunized mice. Control B6 mice, IFN-gamma gene-knockout mice, and EAMG-resistant bm12 mice showed no enhancement of disease. Shifting to a Th1-type antibody isotype distribution was insufficient to cause disease. Other factors, such as direct effects of Th1 cytokines on muscle tissue, may be involved in EAMG susceptibility.

Myasthenia gravis and its animal model: T cell receptor expression in an antibody mediated autoimmune disease

Myasthenia gravis (MG) is a prototypic antibody-mediated autoimmune disease. Since the primary target antigen of the autoimmune response is known and a well-characterized animal model is available, MG is often considered an excellent situation for the application of novel specific immunotherapies, many of which are directed at T lymphocytes. CD4+ helper T cells are required for the development of the animal model, experimental autoimmune MG (EAMG). Even though the target antigen, acetylcholine receptor (AChR) is immunologically complex, the T cell response to AChR in mice is dominated by recognition of a single peptide by about 50% of the T cells. These T cells, in turn, utilize a restricted set of TCR gene elements and conserved CDR3 regions. While specific therapy directed at the immunodominant T cells is capable of reducing the magnitude of the anti-AChR response, considerable flexibility is apparent and reveals the ability of additional T cells to provide the requisite B cell help. In human MG patients, AChR-specific T cells have been identified but in many studies the frequencies were surprisingly low. In a very few cases, AChR-specific T cells have been cloned from MG patients. Analysis reveals heterogeneity in epitope recognition and MHC restriction. Little information on TCR structure is available. Our own studies using antigen-specific as well as non-specific methods for examining clonal T cell expansions in MG have led to an alternative hypothesis concerning T-B collaboration in MG.

The effect of thymectomy on autoreactive T- and B-lymphocytes in myasthenia gravis

Eleven patients with myasthenia gravis were followed for three years after thymectomy. Acetylcholine receptor-specific T-cell stimulation was found in 8/11 patients before operation as compared to 2/11 three years after thymectomy. Changes of T-cell antireceptor-reactivity were commonly paralleled by changes in disease severity. The numbers of cells secreting IL-2 upon stimulation with human acetylcholine receptor correlated with those secreting IFN-gamma. T-cell reactivity against a monoclonal acetylcholine receptor antibody did not decrease after thymectomy. Such reactivity could reflect a beneficial immune response counteracting anti-receptor reactivity. The frequency of autoantibody-secreting cells remained unchanged, while the serum concentration of acetylcholine receptor antibodies started to decrease one year after thymectomy. All examined thymus-cell suspensions contained autoreactive T- and B-lymphocytes. There was a preferential enrichment of autoreactive lymphocytes in the thymus in a few patients with recent onset of disease.

Antigen presentation by interferon-gamma-treated thyroid follicular cells inhibits interleukin-2 (IL-2) and supports IL-4 production by B7-dependent human T cells

The consequence of recognition of antigen on antigen-presenting cells that are induced to express major histocompatibility complex (MHC) class II molecules following an inflammatory process is still not clear. In this study, we have investigated the outcome of antigen presentation by epithelial cells and we have used as a model thyroid follicular cells (TFC) that are known to express MHC class II molecules in autoimmune thyroid diseases and acquire the capacity to present autoantigens to T cells infiltrating the thyroid gland. The result show that MHC class II-expressing TFC were unable to stimulate a primary T cell alloresponse, using CD4+ T cells from three HLA-mismatched responders. Phenotypic analysis showed that TFC, after incubation with interferon-gamma, do not express the costimulatory molecules B7-1 (CD80) and -2 (CD86). Addition of murine DAP.3 cells expressing human B7-1 (DAP.3-B7) to cultures containing peripheral blood CD4+ T cells and DR1-expressing TFC led to a proliferative response, suggesting that the failure of TFC to stimulate a primary alloresponse was due to a lack of co-stimulation. Similarly, HLA-DR-restricted, influenza-specific T cell clones dependent on B7 for co-stimulation did not respond to peptide presented by TFC; again the lack of response could be overcome by co-culture of TFC with DAP.3-B7. Furthermore, recognition of antigen on TFC inhibited interleukin-2 (IL-2) production in the B7-dependent T cells. In contrast, in T helper type 0 (Th0) T cells, IL-4 release was not affected by TFC presentation. In addition, antigen presentation by TFC favored IL-4 production relative to IL-2 production by B7-independent Th0 clones. These results suggest that antigen presentation by MHC class II+ TFC may induce tolerance in autoreactive Th1 cells but may simultaneously favors a Th2 response in uncommitted T cells, and thereby support autoantibody production.

Analysis of T cell responses to the autoantigen in Goodpasture's disease

Goodpasture's disease is a rare form of glomerulonephritis characterized by the production of autoantibodies to the glomerular basement membrane (GBM). In order to understand the development of autoimmunity to the GBM, it is important to examine mechanisms underlying T cell responses to the autoantigen. A MoAb P1, with the same specificity as patients' autoantibodies, was used to affinity-purify the antigen from collagenase-digested human GBM. This material was enriched in the NC1 domain of the alpha 3 chain of type IV collagen (alpha 3(IV)NC1), known to be the principal target of anti-GBM antibodies, but also contained lower quantities of alpha 4(IV)NC1. In proliferation assays, T cells from 11/14 patients with Goodpasture's disease showed significant responses (SI > or = 2.0) to affinity-purified human GBM. Peak responses were demonstrated at 7 or 10 days at antigen concentrations of 10-30 micrograms/ml. As in other autoimmune disorders, the presence of autoantigen-reactive T cells was also demonstrated in 5/10 healthy volunteers. Tissue typing revealed that all patients possessed HLA-DR2 and/or -DR4 alleles, while normal individuals whose T cells responded possessed DR2 and/or DR7 alleles. The specificity of the T cell response in Goodpasture's disease was further investigated using monomeric components of human GBM purified by gel filtration and reverse phase high performance liquid chromatography (HPLC). Two antigenic monomer pools were obtained, which were shown by amino-terminal sequence analysis to contain alpha 3(IV)NC1 and alpha 4(IV)NC1, respectively. In all patients tested, significant T cell proliferation was observed in response to one or both of these alpha (IV)NC1 domains. These results demonstrate that patients with Goodpasture's disease possess T cells reactive with autoantigens known to be recognized by anti-GBM antibodies.

Autoantigen-specific T cell proliferation induced by the ribosomal P2 protein in patients with systemic lupus erythematosus

A role for helper T cells in the induction of pathogenic lupus autoantibodies is increasingly supported by data from studies of murine lupus and patients with systemic lupus erythematosus (SLE). However, the poor in vitro function of SLE T cells has hampered the identification and characterization of autoantigen-specific T cells. We used recombinant fusion proteins to study the T cell proliferative response of 31 lupus patients and 27 healthy subjects to a well-characterized SLE autoantigen, the ribosomal P2 protein. Although PBMC from SLE patients showed marked impairment in the proliferative response to the common recall antigen tetanus toxoid when compared with normal subjects, a significantly greater proportion of SLE patients (32%) than normal individuals (0%) showed a T cell response to a recombinant P2 fusion protein. When the SLE patients were subgrouped according to the presence of serum anti-P autoantibody, 7 of 10 anti-P antibody-positive patients, but 0 of 20 anti-P antibody-negative SLE patients, demonstrated > 2,000 cpm [3H]thymidine incorporation and a P2 stimulation index > 5. The specificity of the T cell proliferative response for the P2 protein was confirmed by studies using a second recombinant human P2 fusion protein and by the specific activation of P2-primed T cells by recombinant P2 in secondary cultures. Moreover, the T cell proliferative response to the P2 autoantigen was mediated by CD4-positive T cells and was inhibited by anti-MHC class II antibodies. These data demonstrate the presence of autoantigen-specific T helper cells in patients with SLE and suggest that these T cells drive the production of autoantibodies by B lymphocytes.

Th1-like cell responses to peripheral nerve myelin components over the course of experimental allergic neuritis in Lewis rats

Experimental allergic neuritis (EAN) is a T cell-mediated animal model of Guillain-Barré syndrome characterized by inflammation and demyelination of peripheral nerves. EAN can be induced by immunization of rats with bovine peripheral nerve myelin (BPM) or the myelin proteins P2 or P0, but the extent of T cell responses over the course of EAN is incompletely defined. We studied the T cell responses to these proteins and the glycolipid GM1 by enumerating T helper type 1 (Th1)-like cells secreting interferon-gamma (IFN-gamma) after short-term culture of mononuclear cells (MNC) in presence of antigen. Already 7 days post immunization (p.i.) with BPM and before onset of clinical EAN, lymph nodes contained elevated levels of P2 responsive T cells. At the height of EAN on day 14 p.i. and during recovery, T cell levels responding to BPM, P0 and GM1 were also elevated. The same temporal profiles and specificities were registered for antigen reactive spleen MNC. The results implicate that Th1-like cells with multiple specificities including the glycolipid GM1 occur at increased levels in lymphoid organs in EAN rats, and that IFN-gamma may be an important effector molecule in the induction of nerve damage.

Acetylcholine receptor-reactive T cells in myasthenia gravis: evidence for the involvement of different subpopulations of T helper cells

Patients with myasthenia gravis have a high prevalence of acetylcholine receptor-specific T lymphocytes in the peripheral blood. Our earlier study shows that these T lymphocytes are stimulated to secrete interferon (IFN)-gamma and interleukin (IL)-2 in response to the autoantigen. Such stimulated T cells may be subdivided into different subsets according to the pattern of cytokine production. In the present study we have investigated the subpopulations of cells by analyzing their IL-4, IFN-gamma and IL-2 secretion pattern. Autoantigen-stimulated IL-4 secretion was found in 55% of the patients, IFN-gamma secretion in 86% and IL-2 secretion in 72%. T lymphocytes from all patients who responded with increased IL-2 secretion also showed increased IFN-gamma secretion. Stimulated IL-4 secretion was detected both in the presence and absence of stimulated IFN-gamma secretion. Depletion of monocytes/macrophages from peripheral blood mononuclear cell preparation and treatment of the cells with a mouse anti-human HLA-DR antibody abolished the secretion of IFN-gamma and IL-4. There were positive correlations between the numbers of IFN-gamma- and IL-2-secreting T cells and the numbers of B cells secreting antibodies against the acetylcholine receptor. Our results show that acetylcholine receptor-stimulated T lymphocytes secrete IL-4, IFN-gamma and/or IL-2. This T cell response is major histocompatibility complex (MHC) class II-restricted and monocyte/macrophage-dependent. Our study indicates that both Th1/Th2 or Th0 subpopulations of the T lymphocytes are involved in the autoimmune response in myasthenia gravis.

HIV antigen-reactive T cells detected by antigen-induced interferon gamma secretion

The T cell repertoire to human immunodeficiency virus (HIV) was studied in HIV-infected patients of different clinical stages by the detection and enumeration of cells that secreted interferon gamma (IFN-gamma) in short-term cultures of blood mononuclear cells after stimulation in vitro with the HIV recombinant antigens pB1, p121, p24-15, gp160bac, and the HIV V3 loop peptide. T cell reactivities to cytomegalovirus (CMV) and Mycobacterium tuberculosis-purified protein derivative (PPD) were examined in parallel. Among 29 patients with HIV infection, 48% had blood cells recognizing one or more of the five HIV antigens. The mean numbers of HIV antigen-reactive T cells varied between 1/approximately 6000 blood cells for pB1 and 1/approximately 20,000 cells for p24-15. None of the five HIV antigens studied was identified as an immunodominant T cell epitope in HIV infection. T cells from 20% of the patients responded to all five HIV antigens in parallel, but the antigen preferentially recognized varied from patient to patient. Those with more advanced disease had a tendency to lower numbers of HIV antigen-reactive T cells. Most HIV-infected patients had both CMV- and PPD-reactive T cells, but numbers were significantly lower in more advanced disease. It should be possible to adopt the present method to evaluate fine specificities of the T cell repertoire to other antigens and to study the involvement of other cytokines besides IFN-gamma, for example, the Th2 cell-related cytokine interleukin 4.

The nicotinic acetylcholine receptor: structure and autoimmune pathology

The nicotinic acetylcholine receptors (AChR) are presently the best-characterized neurotransmitter receptors. They are pentamers of homologous or identical subunits, symmetrically arranged to form a transmembrane cation channel. The AChR subunits form a family of homologous proteins, derived from a common ancestor. An autoimmune response to muscle AChR causes the disease myasthenia gravis. This review summarizes recent developments in the understanding of the AChR structure and its molecular recognition by the immune system in myasthenia.

Immune activation in myasthenia gravis: soluble interleukin-2 receptor, interferon-gamma and tumor necrosis factor-alpha levels in patients' serum

Soluble interleukin-2 receptor (sIL-2R), interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) levels were evaluated in serum from patients affected by myasthenia gravis (MG). sIL-2R titers were significantly increased in generalized and bulbar MG patients while ocular cases were not different from controls. Patients showing a recent clinical worsening had significantly higher sIL-2R titers when compared to the whole MG population. sIL-2R levels did not correlate with the corresponding anti-acetylcholine receptor antibody titer (Anti-AChR Ab). IFN-gamma was not detected in serum of both MG patients and healthy subjects while TNF-alpha levels were not statistically different from controls. The finding of increased sIL-2R levels supports the hypothesis of circulating activated autoreactive T cells in myasthenic patients.

T helper cell recognition of muscle acetylcholine receptor in myasthenia gravis. Epitopes on the gamma and delta subunits

We tested the response of CD4+ cells and/or total lymphocytes from the blood of 22 myasthenic patients and 10 healthy controls to overlapping synthetic peptides, 20 residues long, to screen the sequence of the gamma and delta subunits of human muscle acetylcholine receptor (AChR). The gamma subunit is part of the AChR expressed in embryonic muscle and is substituted in the AChRs of most adult muscles by an epsilon subunit. The delta subunit is present in both embryonic and adult AChRs. Adult extrinsic ocular muscles, which are preferentially and sometimes uniquely affected by myasthenic symptoms, and thymus, which has a still obscure but important role in the pathogenesis of myasthenia gravis, express the embryonic gamma subunit. Anti-AChR CD4+ responses were more easily detected after CD8+ depletion. All responders recognized epitopes on both the gamma and delta subunits and had severe symptoms. In four patients the CD4+ cell response was tested twice, when the symptoms were severe and during a period of remission. Consistently, the response was only detectable, or larger, when the patients were severely affected.

Myasthenia gravis: recognition of a human autoantigen at the molecular level

The symptoms of myasthenia gravis are primarily or exclusively due to an autoimmune response against the muscle nicotinic acetylcholine receptor (AChR) and this has been the object of intensive investigations for almost 20 years. A detailed picture at the molecular level of the interaction of this autoantigen with the key elements involved in the autoimmune response, such as anti-AChR antibodies, the T-cell receptor and restricting major histocompatibility complex molecules, is now emerging for both human myasthenia gravis and its experimental model, experimental autoimmune myasthenia gravis. Here, Maria Pia Protti and colleagues focus on the molecular interactions occurring in human myasthenia gravis and summarize recent information on pathogenic mechanisms of the autoimmune response, and the structure of epitopes recognized by B cells and CD4+ T cells of myasthenic patients on the AChR molecule.

Autoreactive T and B cell responses to myelin antigens after diagnostic sural nerve biopsy

To study whether nervous tissue trauma provokes myelin antigen autoreactive T and B cell responses in humans we examined consecutive blood samples from 7 patients with polyneuropathy undergoing diagnostic sural nerve biopsy and 8 control patients undergoing other types of minor surgery. The antigen-specific T cells were assessed by enumerating cells secreting interferon-gamma (IFN-gamma) in response to the myelin components P0, P2, myelin basic protein (MBP) and myelin associated glycoprotein (MAG), and to 4 selected MBP peptides. B cell mediated immunity was assessed by counting numbers of cells secreting antibodies directed against the myelin proteins. On day 7 after biopsy, there were 3-10-fold increased numbers of T and B cells reactive with P0, P2, MBP and MAG in blood of polyneuropathy patients compared to controls, while levels of cells recognizing purified protein derivate or responding to phytohemagglutinin (PHA) did not differ significantly. Comparison of prebiopsy levels on day 0 with post-biopsy levels on day 7 in the polyneuropathy patients revealed a significant increase in T cells recognizing P0, P2 and MAG, and in B cells secreting IgG antibodies against P0 and P2. On day 14 after nerve biopsy these differences were no longer seen. We suggest that in patients with polyneuropathy, sural nerve biopsy with the ensuing wallerian degeneration and myelin breakdown causes transiently increased levels of circulating myelin autoreactive T and B cells. It remains to be determined if this has a physiological role in nerve trauma responses and/or affects the clinicopathological course of the peripheral neuropathy.

T-cell immunity to acetylcholine receptor and its subunits in Lewis rats over the course of experimental autoimmune myasthenia gravis

Lymph nodes, spleen and thymus obtained from Lewis rats were examined over the course of experimental autoimmune myasthenia gravis (EAMG) for the distribution and the number of antigen-reactive CD4+ T helper cells which, upon recognition of Torpedo acetylcholine receptor (AChR) or the alpha, beta, gamma or delta subunits of Torpedo AChR, responded by secretion of interferon-gamma (IFN-gamma). T cells with these specificities were detected in these three immune organs. Numbers were highest in lymph nodes. In spleen and thymus, numbers of antigen-reactive T cells did not differ. T cells reacting against the intact AChR were more frequent than T cells recognizing any of the subunits. The immunogenicity between the four subunits did not differ, with the exception that the alpha subunit induced a slightly higher T-cell response. No restriction of the T-cell repertoire to the four subunits was detected during early compared to late phases of EAMG. The AChR and subunit-reactive T cells could--via secretion of effector molecules including IFN-gamma--play an important role in the initiation and perpetuation of EAMG, and consequently also of human myasthenia gravis. T cells with the same specificities were also detected in control animals injected with adjuvant only, but at much lower numbers which were within the range of T cells recognizing the control antigen myelin basic protein. They could represent naturally occurring autoimmune T cells.

T cells recognizing multiple peptides of myelin basic protein are found in blood and enriched in cerebrospinal fluid in optic neuritis and multiple sclerosis

The cause of multiple sclerosis (MS) is unknown. Recently reported abnormal T-cell responses to several myelin proteins and myelin basic protein (MBP) peptides in peripheral blood constitute one line of evidence that autoimmune mechanisms could be involved in the pathogenesis of the disease. Monosymptomatic unilateral optic neuritis (ON) is a common first manifestation of MS and important to examine for a possible restriction of the T-cell repertoire early in the disease. T-cell activities to MBP and the MBP amino acid sequences 63-88, 110-128 and 148-165 were examined by short-term cultures of mononuclear cells from cerebrospinal fluid (CSF) and blood in the presence of these antigens, and subsequent detection and counting of antigen-specific T cells that responded by interferon-gamma (IFN-gamma) secretion. Most patients with MS and ON had MBP and MBP peptide-reactive T cells in CSF, amounting to mean values of between about 1 per 2000 and 1 per 7000 CSF cells and without immunodominance for any of the peptides. Numbers were 10-fold to 100-fold lower in the patients' blood. Values were similar in ON and MS, and no evidence was obtained for a more restricted T-cell repertoire in ON. The MBP peptide-recognizing T-cell repertoire was different in CSF than in blood in individual patients with ON and MS, thereby giving further evidence for an autonomy of the autoimmune T-cell response in the CSF compartment. No relations were observed between numbers of autoreactive T cells and presence of oligoclonal IgG bands in CSF or abnormalities on magnetic resonance imaging of the brain in ON or clinical variables of MS. The high numbers of MBP and MBP peptide-reactive T cells could play a role in the pathogenesis of ON via secretion of effector molecules, one of them being IFN-gamma, as well as in the transfer of ON to MS.

Myasthenia gravis: an autoimmune response against the acetylcholine receptor

Myasthenia gravis (MG) is an organ-specific autoimmune disease caused by an antibody-mediated assault on the muscle nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Binding of antibodies to the AChR leads to loss of functional AChRs and impairs the neuromuscular signal transmission, resulting in muscular weakness. Although a great deal of information on the immunopathological mechanisms involved in AChR destruction exists due to well-characterized animal models, it is not known which etiological factors determine the susceptibility for the disease. This review gives an overview of the literature on the AChR, MG and experimental models for this autoimmune disease.

Differential expression of human nicotinic acetylcholine receptor alpha subunit variants in muscle and non-muscle tissues

The nicotinic acetylcholine receptor (nAChR) is an oligomeric transmembrane glycoprotein consisting of four homologous subunits in stoichiometry of alpha 2, beta (gamma or epsilon). Recently the presence of a novel exon (P3A) in human alpha AChR gene has been reported. Two variants of the human alpha subunit arise from alternate RNA splicing, one with and one without the P3A exon. However, the evolutionary origin of the P3A exon and the regulation of the expression of the two variants in human muscle and non-human tissues is currently unknown. Examination of genomic DNA from various species shows that the P3A exon sequence is present only in hominoids, old world and new world primates species and is absent in the muscle cDNA or genomic DNA from rat, mouse or dog, indicating that P3A exon is evolutionary conserved for at least 50 million years. The P3A+ variant of alpha subunit was found to be constitutively expressed in skeletal muscle, brain, heart, kidney, liver, lung and thymus, while P3A-variant was differentially expressed only in skeletal muscle. Thus it appears that the P3A+ variant is generated by 'default' selection by the splicing machinery, while expression of the P3A- variant is regulated by tissue-specific factors in the skeletal muscle. Mechanisms regulating differential expression of the alpha subunit variants may be pertinent to the pathophysiology of myasthenia gravis.

Cytokines in neuroinflammatory disease: role of myelin autoreactive T cell production of interferon-gamma

Many cytokines must be considered as effector and immunoregulatory molecules in neuroinflammatory diseases such as multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). We have studied the potential role of interferon-gamma (IFN-gamma) in the pathogenesis of these diseases, since this cytokine has a number of important effects such as macrophage activation, induction of MHC class I and class I antigens, and T cell homing. An immunospot assay that allows enumeration of single cells secreting IFN-gamma after short-term culture in vitro of mononuclear cell suspensions has been used. In EAE, increased numbers of IFN-gamma-secreting cells (IFN-gamma-sc) appear in the central nervous system shortly before onset of clinical signs. Such cells also increased during pharmacologically induced relapse of EAE. In later stages of EAE, memory T cells that produced IFN-gamma in response to presented antigen, recognized multiple regions of the myelin basic protein (MBP), showing that (i) myelin autoreactive T cells have the functional ability to produce this cytokine, (ii) the concept of immunodominance as to autoantigen peptide reactivity is non-absolute and time-dependent. In multiple sclerosis (MS) there are increased numbers of IFN-gamma-sc among the CSF cells. Also, there are increased numbers of memory T cells, strongly enriched to the cerebrospinal fluid, which upon recognition of several myelin antigens and several MBP peptide stretches, produce IFN-gamma. Taken together, the data are consistent with a role for IFN-gamma as a key mediator in inflammatory demyelinating diseases.

The T-cell repertoire in myasthenia gravis involves multiple cholinergic receptor epitopes

Antibodies against the alpha-subunit of the acetylcholine receptor (AChR) are found in most patients with myasthenia gravis and are considered to contribute to the receptor damage which leads to the characteristic signs and symptoms of the disease. This B-cell response is T-cell driven. Elevated T-cell reactivities to AChR and its alpha-subunit have been described in myasthenia gravis, and AChR alpha-subunit peptide reactive T-cell lines and clones preferentially recognizing certain defined sequence segments have been reported, thereby disclosing the possibility of specific immunotherapy. We have defined the T-cell repertoire to AChR, its alpha-subunit and the synthetic peptide sequences 100-117, 113-130, 143-163, 161-179, 207-225, 221-240, and 235-255 of the alpha-subunit in an immunospot assay which is based on secretion of interferon-gamma (IFN-gamma) by individual memory T cells upon stimulation with specific antigen in short-term cultures. Most patients with myasthenia gravis displayed T-cell reactivities to 1 to 6 different peptides. The mean numbers of T cells recognizing individual peptides varied in the myasthenia gravis patients between 1 per 77,000 and 1 per 167,000 peripheral blood mononuclear cells. None of the seven peptides evaluated could be identified as an immunodominant T-cell epitope, and any of them was found to dominate in individual patients. The numbers of T cells reacting with AChR and recombinant human AChR alpha-subunit were slightly higher (mean numbers 1 per 26,000 and 1 per 50,000 mononuclear cells, respectively). Such cells, as well as AChR alpha-subunit peptide reactive T cells, were also found in patients with other neurological diseases and in healthy subjects, but at lower frequencies and numbers. In myasthenia gravis, the elevated numbers of memory T cells recognizing multiple AChR alpha-subunit peptides may be crucial for the development of the disease, and the IFN-gamma released by such T cells might be important for its perpetuation.

Virus-reactive and autoreactive T cells are accumulated in cerebrospinal fluid in multiple sclerosis

Elevated numbers of B cells--plasma cells secreting antibodies to measles and mumps virus, and to myelin associated glycoprotein (MAG), one of several putative myelin autoantigens--have previously been reported in cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS), while it is unknown if corresponding T cell reactivities occur. We have defined the T cell reactivities to measles and mumps virus and to MAG in an immunospot assay which is based on the detection of secretion of interferon-gamma (IFN-gamma) by single cells upon stimulation with specific antigen in short term cultures. Patients with MS had higher numbers of MAG-reactive T cells in blood compared to controls, while no differences were observed for measles or mumps virus-reactive T cells. In CSF, elevated numbers of MAG-reactive T cells and also of measles- and mumps-reactive T cells were found in patients with MS compared to other neurological diseases. A strong accumulation of antigen-reactive T cells was observed in the MS patients' CSF compared to blood. The magnitude of these T cell reactivities did not correlate with clinical MS variables. The T cell repertoire in MS thus includes, besides myelin basic protein, proteolipid protein and myelin oligodendrocyte glycoprotein, also MAG and, in addition, measles and mumps virus. It is not clear whether these T cell reactivities accumulated in the CSF have importance for the pathogenesis of MS or reflect phenomena secondary to myelin damage, or result from both these alternatives.