Titin antibodies in "seronegative" myasthenia gravis--A new role for an old antigen

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies targeting the neuromuscular junction of skeletal muscles. Triple-seronegative MG (tSN-MG, without detectable AChR, MuSK and LRP4 antibodies), which accounts for ~10% of MG patients, presents a serious gap in MG diagnosis and complicates differential diagnosis of similar disorders. Several AChR antibody positive patients (AChR-MG) also have antibodies against titin, usually detected by ELISA. We have developed a very sensitive radioimmunoprecipitation assay (RIPA) for titin antibodies, by which many previously negative samples were found positive, including several from tSN-MG patients. The validity of the RIPA results was confirmed by western blots. Using this RIPA we screened 667 MG sera from 13 countries; as expected, AChR-MG patients had the highest frequency of titin antibodies (40.9%), while MuSK-MG and LRP4-MG patients were positive in 14.6% and 16.4% respectively. Most importantly, 13.4% (50/372) of the tSN-MG patients were also titin antibody positive. None of the 121 healthy controls or the 90 myopathy patients, and only 3.6% (7/193) of other neurological disease patients were positive. We thus propose that the present titin antibody RIPA is a useful tool for serological MG diagnosis of tSN patients.

Pain and autonomic dysfunction in patients with sarcoidosis and small fibre neuropathy

Small fibre neuropathy (SFN) has been demonstrated in sarcoidosis. However, a systematic analysis of neuropathic pain and autonomic symptoms, key features of SFN, has not been performed. Clinimetric evaluation of pain and autonomic symptoms using the neuropathic pain scale (NPS) and the modified Composite Autonomic Symptoms Scale (mCOMPASS) was used in sarcoidosis patients for this study. A total of 91 sarcoidosis patients (n = 23 without SFN symptoms, n = 43 with SFN symptoms but normal intraepidermal nerve fibre density (IENFD), n = 25 with SFN symptoms and reduced IENFD) were examined. NPS and mCOMPASS were assessed twice (reliability studies). Severity of pain was compared between the subgroups. Correlation between NPS and a visual analogue pain scale (VAS) was assessed (validity studies). Healthy controls (n = 105) completed the mCOMPASS for comparison with patients’ scores. Patients with sarcoidosis, SFN complaints, and reduced IENFD demonstrated more severe pain scores on the NPS. The mCOMPASS differentiated between subjects with and without SFN symptoms. A significant correlation was obtained between the NPS and VAS, indicating good construct validity. Good reliability values were obtained for all scales. The use of the NPS to evaluate SFN symptoms is suggested, as it shows differences between patients with SFN symptoms with normal or reduced IENFD values. The mCOMPASS might be used to select patients for further testing.

Intraepidermal nerve fiber density and its application in sarcoidosis

BACKGROUND

Intraepidermal nerve fiber density (IENFD) is considered a good diagnostic tool for small fiber neuropathy (SFN).

OBJECTIVES

To assess stratified normative values for IENFD and determine the reliability and validity of IENFD in sarcoidosis.

METHODS

IENFD was assessed in 188 healthy volunteers and 72 patients with sarcoidosis (n = 58 with SFN symptoms, n = 14 without SFN symptoms). Healthy controls were stratified (for age and sex), resulting in 6 age groups (20-29, 30-39, ... up to > or = 70 years) containing at least 15 men and 15 women. A skin biopsy was taken in each participant 10 cm above the lateral malleolus and analyzed in accordance with the international guidelines using bright-field microscopy. Interobserver/intraobserver reliability of IENFD was examined. In the patients, a symptoms inventory questionnaire (SIQ; assessing SFN symptoms) and the Vickrey Peripheral Neuropathy Quality-of-Life Instrument-97 (PNQoL-97) were assessed to examine the discriminative ability of normative IENFD values.

RESULTS

There was a significant age-dependent decrease of IENFD values in healthy controls, with lower densities in men compared with women. Good interobserver/intraobserver reliability scores were obtained (kappa values > or = 0.90). A total of 21 patients with sarcoidosis had a reduced IENFD score (< 5th percentile; 19 [32.8%] in patients with SFN symptoms, 2 [14.3%] in patients without SFN symptoms). The validity of the normative IENFD values was demonstrated by distinguishing between the SIQ scores and various PNQoL-97 values for the different patient groups.

CONCLUSION

This study provides clinically applicable distal intraepidermal nerve fiber density normative values, showing age- and sex-related differences.

Immunologic, clinical, and radiologic status 14 months after cessation of natalizumab therapy

OBJECTIVE

Natalizumab is a humanized recombinant monoclonal antibody against very late activation antigen-4 approved for the treatment of patients with multiple sclerosis (MS). A phase II study failed to demonstrate a difference between natalizumab treatment groups and the placebo group with regard to gadolinium enhancing lesions on MRI 3 months after discontinuation of therapy. The objective of this study was to assess clinical MS disease activity, surrogate disease markers on MRI, immunologic parameters in peripheral blood and CSF, as well as safety in patients with MS after discontinuation of natalizumab therapy.

METHODS

This study is a longitudinal and serial cross-sectional assessment, in which 23 patients who were treated with natalizumab in the context of two phase III clinical trials were originally enrolled. A subgroup of patients was followed over 14 months. The annual relapse rate, neurologic disease progression assessed by the Expanded Disability Status Scale, disease surrogate markers on MRI, cellular and humoral immune markers in peripheral blood and CSF, and adverse events of the drug were monitored.

RESULTS

With regard to clinical disease activity, neuroimaging, and immune responses, the majority of patients in our cohort were stable. Decreased lymphocyte cell numbers and altered cell ratios returned to normal 14 months after cessation of natalizumab. No infectious complications were observed.

CONCLUSION

This is the first long-term follow-up of patients who discontinued natalizumab. We did not observe a clinical, radiographic, or immunologic rebound phenomenon after discontinuation of natalizumab therapy.

The features of myasthenia gravis with autoantibodies to MuSK

OBJECTIVES

To determine if myasthenia gravis (MG) with antibodies to MuSK is a distinct subgroup of seronegative MG.

METHODS

We assayed antibodies to muscle specific tyrosine kinase (MuSK) in 55 MG patients who had no antibodies to acetylcholine receptors and looked for the specific phenotype, comparing clinical features of anti-MuSK positive and anti-MuSK negative MG patients.

RESULTS

MG with anti-MuSK antibodies was characterised by a striking prevalence of female patients (15 women, two men). Age at onset ranged from 22 to 52 years, with 70.6% of patients presenting at < 40 years of age. The majority of patients (82.4%) had prevalent involvement of facial and bulbar muscles. One third of them did not respond well to anticholinesterase drugs. Steroid immunosuppression was effective in eight patients (44.4%). Nine patients underwent thymectomy; six of these had no thymus pathology, while three had a hyperplastic thymus. At the end of the observation period, six (35.3%) patients were in remission, five (29.4%) improved, four (23.6%) did not change, and two (11.7%) had died.

CONCLUSIONS

MG patients with antibodies to MuSK have characteristic clinical features that are different from features of the remaining seronegative MG patients. This emphasises the predictive value of anti-MuSK antibody analysis in seronegative MG patients.

Immunoregulation in Experimental Autoimmune Myasthenia Gravis-about T Cells, Antibodies, and Endplates

Experimental autoimmune myasthenia gravis (EAMG) can be induced in a large number of animal species by active immunization (AI) AChR, by passive transfer (PT) of anti-AChR antibodies, by autologous bone marrow transplantation and cyclosporin (BMT-Cy), or spontaneously. Depending on the model used, different immunological mechanisms are operational. In the AI model, the T cell is pivotal in directing the anti-AChR antibody production towards pathogenic, that is, cross-linking and complement-fixing antibodies. Injection of anti-AChR antibodies alone suffices to induce EAMG, excluding the role of specific cell-mediated immune responses in the effector phase of the disease. Aged animals are resistant to the induction of AI and PT EAMG. This resistance is localized at the postsynaptic membrane containing more AChR-anchoring proteins, including S-laminin and rapsyn in aged animals. In BMT-CyA EAMG, a dysregulation of the immune system in the absence of immunization is capable of inducing myasthenia. The role of these animal models in relation to pathogenesis and immunotherapy is discussed.

The role of antibodies in myasthenia gravis

Myasthenia gravis is an autoimmune disease associated with antibodies directed to the postsynaptic acetylcholine receptor. These antibodies reduce the number of receptors. Autoantibodies against AChR and other muscle antigens can be used for the diagnosis of myasthenia gravis and related disorders. The origin and the role of these antibodies in the disease are discussed. Experimental autoimmune myasthenia gravis, an experimental model closely mimicking the disease, has provided answers to many questions about the role of antibodies, complement macrophages and AChR anchor proteins. Genetically modified anti-AChR antibodies may also be used in the future to treat myasthenia.

Small fibre neuropathy in sarcoidosis

Some patients with sarcoidosis have unexplained pain and dysaesthesia. We did quantitative sensory testing in 31 sarcoidosis patients with pain or autonomic dysfunction. 25 patients had reduced warmth sensitivity, cold sensitivity, or both. Intraepidermal nerve fibre density (IENFD) was measured in punch biopsy skin samples in seven consecutive patients. All seven patients had reduced IENFD compared with controls, which confirmed the presence of small fibre neuropathy in these patients. Some patients with sarcoidosis may have small fibre neuropathy with autonomic involvement.

Anti-Hu antibody titre and brain metastases before and after treatment for small cell lung cancer

OBJECTIVES

To follow up the level of anti-Hu antibody titres during chemotherapy and to compare the pattern of metastases and other neurological complications before and after chemotherapy in patients with small cell lung cancer (SCLC) with and without low titre anti-Hu antibodies. Seventeen per cent of patients with SCLC without paraneoplastic syndromes have a low titre of anti-Hu antibodies in their serum. Previous studies suggested that these antibodies correlate with a more indolent tumour growth.

METHODS

The serum of 52 consecutive patients with SCLC were studied before and during chemotherapy, and the correlation with stage of disease and pattern of metastases was examined. All serum samples were investigated using western blot and enzyme linked immunosorbent assay (ELISA) with HuD recombinant protein. All patients with SCLC were investigated using MRI of the brain, CSF, bone marrow aspiration, ultrasound of the abdomen, and radionuclide bone scan.

RESULTS

Nine (17%) of 52 SCLC serum samples were positive by western blot. At the time of diagnosis none of the anti-Hu positive patients had either CNS (brain or leptomeningeal), epidural, adrenal, or bone marrow metastases and 56% had limited disease. In eight of 43 anti-Hu negative patients CNS metastases were found at the time of diagnosis, and only 30% had limited disease. The prevalence of bone and liver metastases was similar in both groups. Survival was 11 (SD ) months for the 43 anti-Hu negative and 10 (SD 6) months for the nine anti-Hu positive patients. Male:female ratio in the anti-Hu negative group was 4.4:1, and in the anti-Hu positive group 2:1.

CONCLUSIONS

No anti-Hu antibody positive serum, as tested by western blot, became negative during chemotherapy. Anti-Hu positive and anti-Hu negative patients had similar survival, but anti-Hu positive patients tended to be women, had limited disease at the time of tumour diagnosis, and initially metastases seemed to spare the nervous system.

Experimental autoimmune myasthenia gravis may occur in the context of a polarized Th1- or Th2-type immune response in rats

Experimental autoimmune myasthenia gravis (EAMG) is a T cell-dependent, Ab-mediated autoimmune disease induced in rats by a single immunization with acetylcholine receptor (AChR). Although polarized Th1 responses have been shown to be crucial for the development of mouse EAMG, the role of Th cell subsets in rat EAMG is not well established. In the present work we show that while the incidence and severity of EAMG are similar in Lewis (LEW) and Brown-Norway (BN) rats, strong differences are revealed in the immune response generated. Ag-specific lymph node cells from LEW rats produced higher amounts of IL-2 and IFN-gamma than BN lymph node cells, but expressed less IL-4 mRNA. IgG1 and IgG2b anti-AChR isotype predominated in BN and LEW rats, respectively, confirming the dichotomy of the immune response observed between the two strains. Furthermore, although IL-12 administration or IFN-gamma neutralization strongly influenced the Th1/Th2 balance in BN rats, it did not affect the disease outcome. These data demonstrate that a Th1-dominated immune response is not necessarily associated with disease severity in EAMG, not only in rats with disparate MHC haplotype but also in the same rat strain, and suggest that in a situation where complement-fixing Ab can be generated as a consequence of either Th1- or Th2-mediated T cell help, deviation of the immune response will not be an adequate strategy to prevent this Ab-mediated autoimmune disease.

Macrophage infiltration at the neuromuscular junction does not contribute to AChR loss and age-related resistance to EAMG

Aged rats resistant to acetylcholine receptor loss in passive transfer experimental autoimmune myasthenia gravis (EAMG) do not reveal infiltrating macrophages at the neuromuscular junction (NMJ) as observed in susceptible rats. It was investigated whether this age-related resistance is due to impaired macrophage function in these aged rats. Reconstitution of aged rats with bone marrow from young donors did not lead to macrophage infiltration, nor did it abolish resistance to EAMG. Subsequently, it was investigated whether macrophages are a primary cause of acetylcholine receptor (AChR) loss in EAMG or are attracted to the NMJ secondary to tissue damage. In lethally irradiated young susceptible rats infiltrating macrophages were absent from the NMJ. However, similar AChR losses were observed in irradiated and non-irradiated rats. These results suggest that macrophages do not contribute to acetylcholine receptor loss in the effector phase of passive transfer EAMG and that age related resistance to passive transfer EAMG is not primarily determined by the absence of infiltrating macrophages.

CT demonstration of aneurysm of a persistent sciatic artery

The CT findings in a case of persistent sciatic artery complicated with an aneurysm in the gluteal area are reported. If on CT an aneurysm is found in the gluteal area, the possibility of an underlying persistent sciatic artery should be considered.

Inhibition of adenylate cyclase activity of human thyroid membranes by gangliosides

Gangliosides inhibit basal, thyrotropin-induced and fluoride-induced adenylate cyclase activity of human thyroid membranes in physiological conditions. In contrast neutral glycolipids, phospholipids and neuraminic acid containing oligosaccharides show no effect. The efficacy of inhibition is more dependent upon the position of the sialic acid residues than upon their absolute number. In general gangliosides with disialyl groups are more inhibitory than those with single sialyl moieties. The inhibitory effects of the individual gangliosides on the two modes of stimulation are parallel. This parallelism suggests that the inhibitory effect is located at the postreceptor level and that the gangliosides interact directly with the adenylate cyclase system. A possible role of thyroid membrane gangliosides as suppressive cofactors of adenylate cyclase is discussed in relation to recent findings of stimulating anti-ganglioside antibodies in Graves' disease.

High degree of idiotypic cross-reactivity among murine monoclonal antibodies to thyroglobulin

The idiotypy of five mouse monoclonal antibodies (mAb) generated against human thyroglobulin (Tg) and reacting with Tg from various species, including murine Tg, was investigated. Rabbit antisera made specific for the idiotype (Id) of three mAb (62, 1.15, and 9.1) were used. By competitive inhibition of homologous Id-anti-Id binding, a surprisingly high degree of Id cross-reactivity was found. The Id determinants on mAb appeared located in or close to the paratope because anti-Id could inhibit their binding to Tg in each instance. Interestingly enough, no true "private" Id could be identified. Id cross-reactivity was found between mAb generated in different fusion experiments and recognizing apparently distinct epitopes on Tg. These results suggest that the immune response to phylogenetically highly conserved epitopes on antigen of internal origin, such as Tg, is idiotypically restricted.

High degree of idiotypic cross-reactivity among murine monoclonal antibodies to thyroglobulin

The idiotypy of five mouse monoclonal antibodies (mAb) generated against human thyroglobulin (Tg) and reacting with Tg from various species, including murine Tg, was investigated. Rabbit antisera made specific for the idiotype (Id) of three mAb (62, 1.15, and 9.1) were used. By competitive inhibition of homologous Id-anti-Id binding, a surprisingly high degree of Id cross-reactivity was found. The Id determinants on mAb appeared located in or close to the paratope because anti-Id could inhibit their binding to Tg in each instance. Interestingly enough, no true "private" Id could be identified. Id cross-reactivity was found between mAb generated in different fusion experiments and recognizing apparently distinct epitopes on Tg. These results suggest that the immune response to phylogenetically highly conserved epitopes on antigen of internal origin, such as Tg, is idiotypically restricted.

Triiodothyronine binding to lymphocyte nuclei and plasma cyclic AMP response to intravenous glucagon in patients with peripheral resistance to thyroid hormones

In vitro studies of nuclear binding of triiodothyronine (T3) in lymphocytes were performed in three members of a family with hereditary peripheral resistance to thyroid hormone action. Ficoll-Hypaque purified lymphocytes were used; the binding characteristics were analyzed by Scatchard's methods. In 5 euthyroid subjects the apparent mean equilibrium association constant (Ka) was 6.2 x 10(9) l/mol and the mean maximal binding capacity (Cap) 14.4 x 10(-15) mol/100 microgram DNA. In the 3 members of the family one single set os saturable T3 nuclear binding sites with affinity constants similar to those in the controls (mean Ka = 3.2 x 10(9) l/mol; mean Cap = 17.4 x 10(-15) mol/100 microgram DNA) were found. The glucagon stimulated increase in plasma cyclic AMP was studied in 6 healthy subjects and the four members of the family. The plasma cyclic AMP levels of the patients with hormone resistance were generally within the normal range. These observations demonstrate that in these patients with peripheral resistance to thyroid hormone binding of T3 to the receptor in the nucleus of lymphocytes is normal; in relation to the high circulating thyroid hormone levels, the thyroid hormone mediated cyclic AMP response is disturbed, suggesting that the defect is at the post-receptor effector level.