Acetylcholine receptor alpha-subunit isoforms are differentially expressed in thymuses from myasthenic patients.

A central role of the thymus in autosensitization to the acetylcholine receptor has been proposed to explain the immunopathogenetic processes in myasthenia gravis (MG). Two isoforms of the alpha-subunit of the acetylcholine receptor are known; they differ by a 25-amino-acid insertion coded by the P3A exon. We investigated the expression of the P3A exon by RNA polymerase chain reaction in fetal and adult human myoblasts and TE671 cells; both isoforms were expressed. Muscle biopsies from patients with MG, Duchenne muscular dystrophy, and polymyositis were also studied and it was again found that both isoforms were expressed, indicating that the P3A exon is not associated with autoimmune, degenerative, and inflammatory muscle diseases. When P3A expression was studied in thymus samples from normal subjects and from thymectomized MG patients, the P3A+ subunit was absent in 75% of patients with involuted thymus and in all patients with thymomas but was present in normal thymuses and in patients with hyperplasia. Differential expression of the alpha-subunit isoforms of the acetylcholine receptor within the thymus may play a role in the immune pathogenesis of MG.

Removal of antiacetylcholine receptor antibodies by protein-A immunoadsorption in myasthenia gravis.

Myasthenia Gravis is an autoimmune disease in which autoantibodies to the acetylcholine receptor interfere with neuromuscular transmission. Plasma exchange is effective in temporarily relieving the symptoms of the disease, but for repeated use the lack of selectivity and need for replacement fluids (which increases the risk of contracting viral diseases) are important drawbacks. Staphylococcal protein A, a potent ligand for immunoglobulins, that interacts negligibly with other plasma proteins, appears to be an optimal candidate for removing antiacetylcholine receptor antibodies, which are mostly IgG. We treated three patients with severe immunosuppression-resistant myasthenia gravis with protein A immunoadsorption. Neurological impairment significantly improved in all patients. After immunoadsorption of 1.5-2 plasma volumes per session, the mean percentage reductions for serum IgG and specific autoantibodies were 71% and 82% respectively. No major side effects occurred. Protein A immunoadsorption appears to be a safe, efficient and effective alternative to plasmaexchange for selected myasthenic patients requiring prolonged apheresis.

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.

Analysis of T cell receptor repertoire of muscle-infiltrating T lymphocytes in polymyositis. Restricted V alpha/beta rearrangements may indicate antigen-driven selection.

Polymyositis is an inflammatory myopathy characterized by mononuclear cell infiltration of muscle tissue. Myocytotoxic T lymphocytes have been recognized in the infiltrates, but the muscle antigen, target of the immune attack, has not been identified. Molecular characterization of the variable regions of T cell receptors (TCRs) on the infiltrating lymphocytes can be expected to provide insights into the pathogenic process. The V alpha/beta TCR repertoire was investigated by RNA-PCR in muscle biopsies from 15 polymyositis patients and 16 controls (6 Duchenne muscular dystrophy and 10 with no inflammatory or dystrophic myopathy). A variety of rearranged variable TCR genes was found in polymyositis, V alpha 1, V alpha 5, V beta 1, and V beta 15 being the most common (present in 60-100% of patients). In Duchenne muscular dystrophy patients TCR V alpha or beta rearrangements were found although no restriction was observed; no rearrangements were found in muscles from the other controls. Sequence analysis revealed the presence of the J beta 2.1 region in 90% of the V beta 15 clones studied, no random N additions in the diversity region, and a common motif within the CDR3 region. These results suggest that selection of muscle-infiltrating T lymphocytes is antigen driven in polymyositis.