CA-antibody: an immunological marker of thymic neoplasia in myasthenia gravis?

Thymic expression of the main immunogenic region of titin in thymomatous myasthenia gravis

Antititin antibody occurs in the serum of myasthenia gravis (MG) patients with thymoma (MGT), and is a diagnostic marker for the disease. The mechanism that triggers MGT development is, however, unclear. This study evaluated the role of the main immunogenic region (MIR) of titin in MGT pathogenesis. Titin MIR antiserum (antibody titre 1:16) was obtained and an in situ immunohistochemical study of thymomatous tissue samples was performed. Strong immunostaining for titin MIR was observed on epithelial cell membranes in MGT patients, and the degree of immunostaining was directly proportional to the number of epithelial cells in thymomatous tissue. Serum antititin antibody levels were closely related to titin MIR levels in thymoma cells; however, titin MIR levels did not appear to be related to MG severity. Antititin antibody may be a good surrogate marker for thymoma but is probably not involved in the pathogenesis of MGT.

The role of complement in myasthenia gravis: serological evidence of complement consumption in vivo

BACKGROUND

Antibodies to the acetylcholine receptor (AChR) titin and the ryanodine receptor (RyR) occur in myasthenia gravis (MG). These antibodies are capable of complement activation in vitro. The involvement of the complement system should cause consumption of complement components such as C3 and C4 in vivo.

MATERIALS AND METHODS

Complement components C3 and C4 were assayed in sera from 78 AChR antibody-positive MG patients and 52 healthy controls. Forty-eight of the patient sera contained titin antibodies as well, and 20 were also RyR antibody-positive.

RESULTS

MG patients with AChR antibody concentrations above the median (11.2 nmol/l) had significantly lower mean C3 and C4 concentrations in serum compared to those with AChR antibody concentrations below the median. Titin antibody-positive MG patients, titin antibody-negative early-onset MG patients, titin antibody-negative late-onset MG patients, and controls had similar C3 and C4 concentrations. Nor did mean C3 and C4 concentrations differ in MG patients with RyR antibodies. Patients with severe MG (grades 4 and 5) had similar C3 and similar C4 levels compared to those with mild MG (grades 1 and 2).

CONCLUSION

An increased in vivo complement consumption was detected in MG patients with high AChR antibody concentrations, unrelated to MG severity and non-AChR muscle antibodies.

Thymectomy and anti-muscle autoantibodies in late-onset myasthenia gravis

Thymectomy is still widely carried out in myasthenia gravis (MG) patients, but its role, especially in late-onset MG patients, is not established. These patients are immunologically heterogeneous, some with thymoma-like and others with early onset-like features. We evaluated whether any therapeutic effects of thymectomy correlate with the presence of non-acetylcholine receptor (AChR) muscle antibodies. The severity of MG, and titin and ryanodine receptor (RyR) antibodies, were assessed yearly starting from MG onset in 21 thymectomized and 22 non-thymectomized AChR antibody positive late-onset MG patients, who were followed for 2, 3 and 5 years. Clinical or pharmacological remission were seen in six of 11 titin antibody negative but none of the 10 titin antibody positive thymectomized patients, however, the non-thymectomized cases showed an opposite trend. The three MG-related deaths were all in patients with titin antibodies. There was no significant difference in MG severity between thymectomized and non-thymectomized patients; 2 years after MG onset, both groups were significantly improved. This study showed no dramatic benefit from thymectomy in late-onset MG in general. Any limited improvement appeared less likely in cases with titin and/or RyR antibodies.

Complement activation by titin and ryanodine receptor autoantibodies in myasthenia gravis. A study of IgG subclasses and clinical correlations

To elucidate the mechanism of immune damage caused by titin and ryanodine receptor (RyR) autoantibodies in myasthenia gravis (MG), we studied the complement-activating capacity and the IgG subclass distribution of these autoantibodies in sera from 49 MG patients. Complement activation occurred in 38 out of 49 titin antibody positive sera, and in 14 out of 21 RyR antibody positive sera. The titin antibodies occurred only in the IgG 1 and IgG 4 subclasses, whereas the RyR antibodies occurred in all four IgG subclasses but with IgG 1 predominance. Complement-activating RyR antibodies occurred with higher frequency in sera of thymoma MG than of late-onset MG. RyR IgG 1 antibodies occurred more often in severe MG than in mild and moderate disease groups. Mean total IgG and IgG 1 titin and RyR antibody titers fell during long-time patient observation together with an improvement of the MG symptoms.

An enzyme-linked immunosorbent assay for antibodies against acid soluble skeletal muscle antigen in myasthenia gravis

An enzyme-linked immunosorbent assay (ELISA) system has been developed for measuring serum antibodies against citric-acid extract of human skeletal muscles. With this assay, 80% of myasthenia patients with thymoma gave positive results. No sera from patients with neurological diseases other than myasthenia gravis (MG) gave positive results. The result of this study indicates that the ELISA system is useful as an adjunct for the diagnosis of MG particularly in the patients associated with thymoma and that the ELISA method can also be used as a prognostic marker following thymectomy in patients with MG.

Antibodies to skeletal muscle in myasthenia gravis. Part 1. Diagnostic value for the detection of thymoma

The role of anti-muscle antibodies (AMA) in the diagnosis of thymoma in patients with myasthenia gravis (MG) is evaluated. We compared ELISA and Western blot assay for antibodies to citric acid muscle extract (a-CAE) with an immunofluorescence assay (IF). Sera from 234 selected MG patients and 123 controls were tested. There was no essential difference between ELISA and IF. Western blot was superior in young onset patients but less useful in patients with an onset beyond the age of 40 years. Unusually high post-test probabilities were found by our patient selection criteria which seem most realistic for clinical practice. Western blot revealed no differences in specificity of AMA in thymoma and non-thymoma patients irrespective of age at onset of disease.

Myasthenia gravis muscle antibodies examined by ELISA: IgG and IgM antibodies characterize different patient subgroups

Sera from 90 myasthenia gravis (MG) patients were examined for antibodies against skeletal muscle citric acid extract (CA) antigens by ELISA and indirect haemagglutination (IHA). 31% (ELISA) and 24% (IHA) of the sera were positive, and the results of the two tests were in good agreement. 18 of 28 patients positive in ELISA had IgG CA-antibodies, 10 had IgM and 3 IgA CA-antibodies. The patients with IgG antibodies had a high mean age of MG disease onset, and 9/14 thymectomized patients had a thymoma. Patients with IgM CA-antibodies had a much lower age of onset and 4/5 thymectomized patients had thymus hyperplasia. IgM antibody positive patients had a long disease duration, indicating that they produce IgM antibodies for an indefinite period of time without switching to IgG antibody production.

Anti-skeletal muscle and anti-acetylcholine receptor antibodies in patients with thymoma without myasthenia gravis: relation to the onset of myasthenia gravis

We measured the anti-skeletal muscle (SM) antibody titers in sera from 46 patients with thymoma but without Myasthenia gravis (MG) in order to determine whether the presence of anti-SM antibody is linked to the combination of thymoma-MG, or to thymoma alone. We detected anti-SM antibodies in 18 of these sera, of which 15 had concomitantly elevated titers of anti-AChR antibodies. Moreover, 9 of whom had experienced the onset of MG after surgery. In contrast, no patient without elevations in both antibodies developed MG during the followup. We conclude that the presence of anti-SM antibodies is linked strongly with thymoma associated with MG, but not with thymoma alone.

Patients with myasthenia gravis and thymoma have in their sera IgG autoantibodies against titin

Patients with myasthenia gravis (MG) and thymoma have in their sera antibodies which react with non-receptor antigens from striated muscle. The purpose of this investigation was to characterize the antigen(s). Polypeptides in homogenates from rat skeletal muscle were separated by SDS-PAGE and trans-blotted to nitrocellulose. Sera from six patients with MG and thymoma stained a large (molecular weight greater than 500 kD) polypeptide, while no staining was observed with sera from 20 non-thymoma MG patients. Titin is one of the large (greater than 500 kD) polypeptides of striated muscle and the antibody containing MG sera have antibodies that bind to titin in a preparation of myofibrillary proteins from rabbit skeletal muscle. The staining pattern is identical to that obtained with antiserum to titin, showing that the antigen has the same electrophoretic mobility as titin. Antibodies from the sera of the patients with MG and thymoma, affinity-purified on the large polypeptide, reacted with skeletal muscle sections in a cross-striational pattern, near the A/I band junction but within the I band, corresponding to the localization of one of the epitopes of titin. Our findings therefore indicate that the muscle antibodies found in the sera from some MG patients with thymoma are directed against titin.

Immunoglobulin allotypes in myasthenia gravis patients with a thymoma

Gm and Km allotypes were examined in 29 myasthenia gravis patients with a thymoma and non-receptor skeletal muscle antibodies. The frequency of the phenotype Gm1,2,3;23;5,21 was significantly higher in the patients than in 292 healthy controls (P less than 0.01). Km allotype frequencies did not differ in patients and controls.

Anti-skeletal muscle antibodies in the sera from myasthenic patients with thymoma: identification of anti-myosin, actomyosin, actin, and alpha-actinin antibodies by a solid-phase radioimmunoassay and a western blotting analysis

We recently reported a strong association between the occurrence of anti-skeletal muscle (SM) antibodies and the presence of thymoma in patients with myasthenia gravis (MG). To further examine the immunoreactivity of MG sera against human muscle antigens, we developed a solid-phase radioimmunoassay (RIA) using purified muscle antigens and a Western blotting analysis in MG sera with high titers of anti-SM antibodies. Our results showed that MG patients with thymoma (thymoma group) had markedly high titers of anti-myosin and anti-actomyosin antibodies than those without thymoma (non-thymoma group). Furthermore, a close correlation was found between titers of anti-SM, anti-myosin and anti-actomyosin antibodies. The antibody titers against actin, alpha-actinin and tropomyosin were all low and did not correlate with titers of anti-SM antibodies. But, significant levels of these three antibodies were found in the thymoma group. By a Western blotting analysis, immunoreactivity of sera from the thymoma group appeared to be predominantly directed against myosin, actin and alpha-actinin.

Anti-neuroblastoma antibodies in myasthenia gravis: clinical and immunological correlations

Forty-four of 109 myasthenia gravis (MG) patients (40%) had serum antibodies against human neuroblastoma cells (NBL). Anti-NBL antibodies were most frequent in the sera of MG patients who had either a hyperplastic thymus or a thymoma, clinically mild to moderately severe generalized MG, and a long disease duration (greater than or equal to 11 years). No correlation between individual anti-NBL antibody and anti-acetylcholine receptor (AChR) antibody titers was observed. Seven of the 19 patients negative for anti-AChR antibodies (37%) had anti-NBL antibodies in their sera. These findings provide further evidence for immunological heterogeneity in MG. In addition to the typical autoantibodies to the AChR, autoimmunization against neural antigens can frequently be detected in these patients.