Leslie Jacobson

Antibodies in Myasthenia Gravis and Related Disorders

Abstract: Acetylcholine receptor (AChR) antibodies are present in around 85% of patients with myasthenia gravis (MG) as measured by the conventional radioimmunoprecipitation assay. Antibodies that block the fetal form of the AChR are occasionally present in mothers who develop MG after pregnancy, especially in those whose babies are born with arthrogryposis multiplex congenita. The antibodies cross the placenta and block neuromuscular transmission, leading to joint deformities and often stillbirth. In these mothers, antibodies made in the thymus are mainly specific for fetal AChR and show restricted germline origins, suggesting a highly mutated clonal response; subsequent spread to involve adult AChR could explain development of maternal MG in those cases who first present after pregnancy. In the 15% of “seronegative” MG patients without AChR antibodies (SNMG), there are serum factors that increase AChR phosphorylation and reduce AChR function, probably acting via a different membrane receptor. These factors are not IgG and could be IgM or even non‐Ig serum proteins. In a proportion of SNMG patients, however, IgG antibodies to the muscle‐specific kinase, MuSK, are present. These antibodies are not found in AChR antibody‐positive MG and are predominantly IgG4. MuSK antibody positivity appears to be associated with more severe bulbar disease that can be difficult to treat effectively.

Plasma from human mothers of fetuses with severe arthrogryposis multiplex congenita causes deformities in mice.

Arthrogryposis multiplex congenita (AMC) is characterized by fixed joint contractures and other deformities, sometimes resulting in fetal death. The cause is unknown in most cases, but some women with fetuses affected by severe AMC have serum antibodies that inhibit fetal acetylcholine receptor (AChR) function, and antibodies to fetal antigens might play a pathogenic role in other congenital disorders. To investigate this possibility, we have established a model by injecting pregnant mice with plasma from four anti-AChR antibody-positive women whose fetuses had severe AMC. We found that human antibodies can be transferred efficiently to the mouse fetus during the last few days of fetal life. Many of the fetuses of dams injected with AMC maternal plasmas or Ig were stillborn and showed fixed joints and other deformities. Moreover, similar changes were found in mice after injection of a serum from one anti-AChR antibody-negative mother who had had four AMC fetuses. Thus, we have confirmed the role of maternal antibodies in cases of AMC associated with maternal anti-AChR, and we have demonstrated the existence of pathogenic maternal factors in one other case. Importantly, this approach can be used to look at the effects of other maternal human antibodies on development of the fetus.

The search for new antigenic targets in myasthenia gravis

Around 80% of myasthenia gravis patients have antibodies against the acetylcholine receptor, and 0–60% of the remaining patients have antibodies against the muscle‐specific tyrosine kinase, MuSK. Another recently identified antigen is low‐density lipoprotein receptor‐related protein 4 (Lrp4). To improve the existing assays and widen the search for new antigenic targets, we have employed cell‐based assays in which candidate target proteins are expressed on the cell surface of transfected cells and probed with patient sera. These assays, combined with use of myotube cultures to explore the effects of the antibodies, enable us to begin to identify new antigenic targets and test antibody pathogenicity in vitro.

Scenarios for Autoimmunization of T and B Cells in Myasthenia Gravis

Abstract: We have studied responses in thymoma patients to interferon‐α and to the acetylcholine receptor (AChR) in early‐onset myasthenia gravis (EOMG), seeking clues to autoimmunizing mechanisms. Our new evidence implicates a two‐step process: (step 1) professional antigen‐presenting cells and thymic epithelial cells prime AChR‐specific T cells; then (step 2) thymic myoid cells subsequently provoke germinal center formation in EOMG. Our unifying hypothesis proposes that AChR epitopes expressed by neoplastic or hyperplastic thymic epithelial cells aberrantly prime helper T cells, whether generated locally or infiltrating from the circulation. These helper T cells then induce antibody responses against linear epitopes that cross‐react with whole AChR and attack myoid cells in the EOMG thymus. The resulting antigen‐antibody complexes and the recruitment of professional antigen‐presenting cells increase the exposure of thymic cells to the infiltrates and provoke local germinal center formation and determinant spreading. Both these and the consequently enhanced heterogeneity and pathogenicity of the autoantibodies should be minimized by early thymectomy.

A transfected human muscle cell line expressing the adult subtype of the human muscle acetylcholine receptor for diagnostic assays in myasthenia gravis

Immunoprecipitation of human acetylcholine receptor (AChR) is used in the diagnostic assay for myasthenia gravis (MG).We compared human AChR derived from TE671 cells, which express fetal-type AChR, with AChR from TE671-epsilon cells, which we have engineered to express adult-type AChR. Some low-titer MG sera distinguished strikingly between the two subtypes. Four out of seven MG sera that had equivocal titers in standard assays gave positive titers with TE671-epsilon AChR, whereas only one out of seven gave a positive titer with TE671 cells. The new cell line provides a greater concentration of adult AChR than can be obtained from normal human muscle and increases the sensitivity of the diagnostic assay. NEUROLOGY 1996;47: 1552-1555

Clinical relevance of serum antibodies to extracellular N-methyl-d-aspartate receptor epitopes

Objective There are now a large number of requests for N-methyl-d-aspartate receptor autoantibody (NMDAR-Ab) tests, and it is important to assess the clinical relevance of all results, particularly when they are reported as ‘Low Positive’. Methods The clinical data of 56 patients found Positive or Low Positive by the Oxford live cell-based assay were reviewed. An autoimmune basis for the condition was assigned as ‘Definite’, ‘Possible’ or ‘Unlikely’. The number of core features (encephalopathy, psychiatric, cognitive, epileptic, extrapyramidal and inflammatory cerebrospinal fluid (CSF)) was tabulated. Results Twenty-five (44.6%) patients had a Definite NMDAR-Ab encephalitis (eight ovarian teratomas, one Hodgkins lymphoma), 18 (32.1%) a Possible NMDAR-Ab encephalitis and 13 (23.2%) an Unlikely autoimmune syndrome. Serum NMDAR-Ab levels were higher in patients with tumours. Positive NMDAR-Abs were found not only in patients with three or more core features and a Definite syndrome, but also in five patients classified as Possible. Conversely, Low Positive NMDAR-Abs were present in 7 Definite cases as well as in 13 Possible cases. Unlikely patients had mainly Low Positive antibodies and fewer core features. CSF NMDAR-Abs, only available in 11 pairs and at varying time points, broadly related to serum levels and were Positive in 3/3 patients with tumours but in only 2/5 Definite patients, and none of the Possible or Unlikely cases. Interpretation Using live cell-based assays, Positive and Low Positive antibodies can be of clinical significance. The number of core clinical features should help to select those patients in whom an immunotherapy intervention might be considered, irrespective of the antibody level.

NMDA receptor antibodies associated with distinct white matter syndromes

Objective: To report the clinical and radiologic findings of children with NMDA receptor (NMDAR) antibodies and white matter disorders. Method: Ten children with significant white matter involvement, with or without anti-NMDAR encephalitis, were identified from 46 consecutive NMDAR antibody–positive pediatric patients. Clinical and neuroimaging features were reviewed and the treatment and outcomes of the neurologic syndromes evaluated. Results: Three distinct clinicoradiologic phenotypes were recognized: brainstem encephalitis (n = 3), leukoencephalopathy following herpes simplex virus encephalitis (HSVE) (n = 2), and acquired demyelination syndromes (ADS) (n = 5); 3 of the 5 with ADS had myelin oligodendrocyte glycoprotein as well as NMDAR antibodies. Typical NMDAR antibody encephalitis was seen in 3 patients remote from the first neurologic syndrome (2 brainstem, 1 post-HSVE). Six of the 7 patients (85%) who were treated acutely, during the original presentation with white matter involvement, improved following immunotherapy with steroids, IV immunoglobulin, and plasma exchange, either individually or in combination. Two patients had escalation of immunotherapy at relapse resulting in clinical improvement. The time course of clinical features, treatments, and recoveries correlated broadly with available serum antibody titers. Conclusion: Clinicoradiologic evidence of white matter involvement, often distinct, was identified in 22% of children with NMDAR antibodies and appears immunotherapy responsive, particularly when treated in the acute phase of neurologic presentation. When observed, this clinical improvement is often mirrored by reduction in NMDAR antibody levels, suggesting that these antibodies may mediate the white matter disease.

Early‐onset myasthenia gravis: A recurring T‐cell epitope in the adult‐specific acetylcholine receptor ε subunit presented by the susceptibility allele HLA‐DR52a

No immunodominant T‐cell epitopes have yet been reported in the human acetylcholine receptor (AChR), the target of the pathogenic autoantibodies in myasthenia gravis (MG). We have selected and characterized T cells from MG patients by restimulation in culture with recombinant human AChR α, γ, and ε subunits; the γ and ε distinguish the fetal and adult AChR isoforms, respectively. We obtained clones specific for the ε, rather than the α or γ, subunit in 3 of the first 4 early‐onset MG cases tested. They all responded to peptide ε201–219 and to low concentrations of adult but not fetal AChR. Moreover, although using different T‐cell receptor genes, they were all restricted to HLA‐DR52a (DRB3*0101), a member of the strongly predisposing HLA‐A1‐B8‐DR3 haplotype. This apparently immunodominant ε201–219 epitope (plus DR52a) was also recognized by clones from an elderly patient whose MG had recently been provoked by the drug D‐penicillamine. In all 4 cases, however, the serum antibodies reacted better with fetal than adult AChR and may thus be end products of determinant spreading initiated by adult AChR‐specific T cell responses. Furthermore, as these T cells had a pathogenic Th1 phenotype, with the potential to induce complement‐activating antibodies, they should be important targets for selective immunotherapy. Ann Neurol 1999;45:224–231

N-methyl-D-aspartate receptor antibody-mediated neurological disease: results of a UK-based surveillance study in children

Objective N-methyl-D-aspartate receptor antibody (NMDAR-Ab) encephalitis is a well-recognised clinico-immunological syndrome that presents with neuropsychiatric symptoms cognitive decline, movement disorder and seizures. This study reports the clinical features, management and neurological outcomes of paediatric NMDAR-Ab-mediated neurological disease in the UK. Design A prospective surveillance study. Children with NMDAR-Ab-mediated neurological diseases were voluntarily reported to the British Neurological Surveillance Unit (BPNSU) from November 2010 to December 2011. Initial and follow-up questionnaires were sent out to physicians. Results Thirty-one children fulfilled the criteria for the study. Eight presented during the study period giving an incidence of 0.85 per million children per year (95% CI 0.64 to 1.06); 23 cases were historical. Behavioural change and neuropsychiatric features were present in 90% of patients, and seizures and movement disorders both in 67%. Typical NMDAR-Ab encephalitis was reported in 24 children and partial phenotype without encephalopathy in seven, including predominantly psychiatric (four) and movement disorder (three). All patients received steroids, 22 (71%) received intravenous immunoglobulin, 9 (29%) received plasma exchange,and 10 (32%) received second-line immunotherapy. Of the 23 patients who were diagnosed early, 18 (78%) made a full recovery compared with only 1 of 8 (13%) of the late diagnosed patients (p=0.002, Fishers exact test). Seven patients relapsed, with four needing additional second-line immunotherapy. Conclusions Paediatric NMDAR-Ab-mediated neurological disease appears to be similar to adult NMDAR-Ab encephalitis, but some presented with a partial phenotype. Early treatment was associated with a quick and often full recovery.

Investigation of neuronal autoantibodies in two different focal epilepsy syndromes

Neuronal antibodies have been identified in patients with seizures as the main or sole symptom. Our aim was to investigate the prevalence of these autoantibodies in patients with focal epilepsy of unknown cause (FEoUC) and in the group having mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE‐HS).