Increased incidence of certain TCR and HLA genes associated with myasthenia gravis in Italians

Prospects for a T-cell receptor vaccination against myasthenia gravis

T-cell receptor (TCR) vaccination has been proposed as a specific therapy against autoimmune diseases. It is already used in clinical trials, which are supported by pharmaceutical companies for the treatment of multiple sclerosis, rheumatoid arthritis and psoriasis. Current vaccine developments are focusing on enhancement of immunogenicity as well as selecting the best route of immunization and adjuvant to favor the therapeutic effect. In the meantime, academic laboratories are tackling the regulatory mechanisms involved in the beneficial effect of the vaccines to further understand how to control the therapeutic tool. Indeed, several examples in experimental models of autoimmune diseases indicate that any specific therapy may rely on a delicate balance between the pathogenic and regulatory mechanisms. This review presents a critical analysis of the potential of such therapy in myasthenia gravis, a prototype antibody-mediated disease. Indeed, a specific pathogenic T-cell target population and a TCR-specific regulatory mechanism mediated by anti-TCR antibodies and involved in protection from the disease have recently been identified in a patient subgroup. The presence of spontaneous anti-TCR antibodies directed against the pathogenic T-cells that may be boosted by a TCR vaccine provides a rationale for such therapy in myasthenia gravis. The development of this vaccine may well benefit from experience gained in the other autoimmune diseases in which clinical trials are ongoing.

No association of the HLA-DQ alleles with myasthenia gravis in Cuban patients

Myasthenia gravis (MG) is a neuromuscular disorder characterized by fatigability and weakness of striated muscles. Its association with HLA molecules is well known and varies depending on age, sex and the ethnicity of the patients. A case-control study was performed in 61 Cuban patients and 81 controls using polymerase chain reaction and sequence-specific primers of the HLA-DQA1/B1 alleles. The distribution of the HLA-DQ alleles individually and in a simple haplotype between patients and controls shows no statistically significance differences. This result could be due to the heterogeneity and ethnic admixture existing in Cuban population. These findings indicate that the association between a disease and a particular genetic region cannot be explained merely by similarities in the genetic background but involve environmental and immunological factors.

Myasthenia gravis: clinical, immunological, and therapeutic advances

We give an update on clinical, immunological, and therapeutic advances in the field of myasthenia gravis, including a summary of suggested therapeutic recommendations.

Genetics of autoimmune myasthenia gravis, a model for antibody-mediated autoimmunity in man

Autoimmune myasthenia gravis is an antibody-mediated autoimmune disease of the neuromuscular junction aimed at the muscle acetylcholine receptor. Recent genetic analyses focusing on a nonclass II HLA-linked locus, MYAS1, and on one of the genes encoding the AChR self-antigen, CHRNA1, are discussed.

IL-1 genes in myasthenia gravis: IL-1A -889 polymorphism associated with sex and age of disease onset

Myasthenia gravis (MG) is a multifactorial autoimmune disease of the neuromuscular junction. We investigated the relation between four polymorphisms of the interleukin (IL)-1 gene cluster on 2q12-22, and MG susceptibility and clinical features in a large cohort of individuals. No polymorphism was associated with MG susceptibility. However, the IL-1A -889 CC genotype was associated with early disease onset (p=0.0044) in the whole MG group and the subgroup of CC males developed MG about 18 years earlier than males carrying other IL-1A -889 genotypes (p=0.022). This finding suggests that IL-1A is a disease modifier in MG, or is in linkage disequilibrium with an unknown locus on chromosome 2.

HLA-DQ6 transgenic mice resistance to experimental autoimmune myasthenia gravis is linked to reduced acetylcholine receptor-specific IFN-gamma, IL-2 and IL-10 production

To comprehend the reduced susceptibility of HLA-DQ6 transgenic mice in comparison with HLA-DQ8 mice, to experimental autoimmune myasthenia gravis (EAMG), we immunized them with acetylcholine receptor (AChR) and examined in vitro, the proliferative and cytokine responses to AChR. When immunized with AChR and examined for AChR-specific lymphocyte responses to AChR, EAMG-resistant DQ6 mice exhibited significantly reduced in vitro lymphoproliferative and cytokine responses to AChR, compared to DQ8 mice. The differences in susceptibility were not linked to a difference in peptide recognition by AChR-specific lymphocytes. AChR T cell epitope mapping showed that both DQ6 and DQ8 responded to the same epitopes, although to varying degrees. Resistance of DQ6 transgenic mice to EAMG was linked to a dramatic suppression of AChR-specific IFN-gamma, IL-2 and IL-10 productions by AChR-primed lymph node cells.

beta2-adrenergic receptor gene polymorphisms in myasthenia gravis (MG)

The beta2-adrenergic receptor (beta2-AR) belongs to the group of G-protein coupled receptors and is present mainly on skeletal and cardiac muscle cells and lymphocytes. The gene encoding beta2-AR (ADRB2) displays a moderate degree of heterogeneity in the human population. The distribution of polymorphisms at amino acid positions 16, 27 and 164 is changed in asthma, hypertension and obesity. We have earlier reported a decreased density of the beta2-AR on peripheral blood mononuclear cells and the presence of beta2-AR antibodies in patients with MG. Since certain polymorphisms affect the function of the beta2-AR, it was of interest to analyse these in MG. Using allele-specific polymerase chain reaction amplification, we revealed an over-representation of homozygosity for Arg16 and a lower prevalence of homozygosity for Gly16 in MG patients compared with healthy individuals. The increased frequency of homozygosity for Arg16 was due to a contribution from patients with generalized MG but not from patients with only ocular disease. Homozygosity for Glu27 was negatively associated with both the presence of beta2-AR antibodies and severity of disease. Moreover, acetylcholine receptor (AChR) antibodies were more often present in patients being homozygous for Gln27. Our results imply that homozygosity for Arg16 confers susceptibility to generalized MG, and that certain polymorphisms at amino acid position 27 are associated with subgroups of patients.

Different HLA-DQ are positively and negatively associated in Swedish patients with myasthenia gravis

The aim of this study was to determine the association between HLA-DQ and myasthenia gravis (MG) in 79 Swedish patients and 155 unrelated population based controls. HLA genotyping was done using polymerase chain reaction combined with sequence specific oligonucleotide probes. The DQB allele, DQB1*0201 was positively associated with MG, 39/79 (49%) patients and 43/152 (28%) controls (OR 2.47, Pc = 0.037). DQB1*0201 was observed more frequently in patients with an early onset of disease, below 30 years (Pc = 0.033). A negative association was found for DQA1*0103, 7/78 (9%) patients and 38/154 (25%) controls (OR 0.30, Pc = 0.037). DQA1*0501-DQB1*0201 and DQA1*0201-DQB1*0201 together was significantly increased in patients when compared to controls (OR 2.68; Pc = 0.019). In conclusion, two different DQ2 haplotypes (DQA1*0501-DQB1*0201 and DQA1*0201-DQB1*0201) were positively and the DQA1*0103 allele was negatively associated with MG. Susceptibility and resistance to MG in Swedish patients is mediated by HLA-DQ.

Identification by genomic typing of non-DR3 HLA class II genes associated with myasthenia gravis

HLA association with myasthenia gravis (MG) has been studied in a series of 114 patients using class I and class II genotyping after PCR amplification. Positive association was found with DR3, particularly in women (RR = 2.6) and in early MG onset (RR = 3.4). DRB1, DRB3, DQB1, DQA1 and B (B8 and B18) genotyping revealed that the association was predominantly with the B8 DRB1*03 DRB3*0101 DQB1*0201 DQA1*0501 ancestral haplotype. This haplotype frequency was also increased in patients with thymic hyperplasia (RR = 3.5) and was greatly reduced in patients with thymoma (RR = 0.35). Sixteen out of 48 patients carrying this 8.1 ancestral haplotype showed absence of B8 (n = 4) or of DR3 (n = 12). HLA class II genotyping further revealed the existence of two other significant associations. MG was positively associated with the DQB1*0604 allele (RR = 3.4), particularly in patients with thymoma (RR = 5.7). Furthermore, the disease was negatively associated with DR1 in females (RR = 0.32). These data suggest that MG is placed under the control of at least three distinct genes: (1) a class II predisposing gene in the 8.1 ancestral haplotype; (2) a thymoma-associated class II allele on the DQB1*0604 haplotype; and (3) a protective allele DR1.

Restricted Vα2.3 gene usage by CD4+ T lymphocytes in bronchoalveolar lavage fluid from sarcoidosis patients correlates with HLA-DR3

The alpha/beta T cell receptor (TcR) V gene usage of bronchoalveolar lavage (BAL) lymphocytes and peripheral blood lymphocytes (PBL) from 11 sarcoidosis patients and 4 healthy controls was investigated, using eight alpha/beta TcR V gene product-specific monoclonal antibodies (mAb). Twenty-seven percent (3/11) of the sarcoidosis patients had a highly significant increase in V alpha 2.3+CD4+ T lymphocytes in the bronchoalveolar space, while displaying normal frequencies of these T cells in peripheral blood. The reactivities with the remaining seven TcR mAb were normal. In the control group, no compartmentalization of any T cells was seen. Four of the patients expressed the HLA-DR3 (w17), DQw2 haplotype. Interestingly, the three patients with distinct signs of compartmentalized V alpha 2.3+CD4+ T cells all expressed this HLA haplotype. Additionally, a fourth patient with pronounced, although less significant, accumulation of V alpha 2.3+CD4+ T cells in the lung, was also HLA-DR3(w17), DQw2+. Expression of V alpha 2.3+CD4+ T cells in BAL of these patients correlated with clinical disease, as revealed on re-analyzing the four patients after 6 months or longer. Predominant TcR V alpha 2.3 gene usage in compartmentalized CD4+ BAL T lymphocytes, linked to HLA-DR3(w17), DQw2 haplotype, may thus indicate presence of a specific antigen localized to the lungs of sarcoidosis patients.

Abnormal T-cell expansion and V-gene usage in myasthenia gravis patients

To determine the extent of V-gene heterogeneity of blood T lymphocytes in patients suffering from Myasthenia Gravis (MG), we used eight recently available monoclonal antibodies (MoAb), directed against different V alpha and V beta gene products of the variable part of the T-cell receptor (TCR), covering approximately 25% of the alpha/beta T cells in normal peripheral blood (PBL) of healthy individuals. Using a two-colour immunofluorescence method, we could calculate the expression of alpha/beta V segments within the two major T-cell subsets, CD4-/CD8+ and CD4+/CD8- lymphocytes. Twenty-seven per cent (4/15) of the MG patients had T cells showing signs of abnormal expansion. Furthermore, among these expanded T cells, a restricted V beta 12 gene expansion could be seen, in three out of four patients. No correlation between TCR V-gene usage and HLA haplotypes (HLA-A, -B, -DR and -DQ) could be seen. Our data suggest that the majority of MG patients have abnormally expanded T-cell clones. The relevance of these findings is discussed.