Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies

BACKGROUND

Idiopathic autonomic neuropathy is a severe, subacute disorder with a presumed autoimmune basis. It is indistinguishable from the subacute autonomic neuropathy that may accompany lung cancer or other tumors. Autoantibodies specific for nicotinic acetylcholine receptors in the autonomic ganglia are potentially pathogenic and may serve as serologic markers of various forms of autoimmune autonomic neuropathy.

METHODS

We tested serum from 157 patients with a variety of types of dysautonomia. Immunoprecipitation assays with iodine-125-labeled epibatidine and solubilized human neuroblastoma acetylcholine receptors were used to detect autoantibodies that bound to or blocked ganglionic receptors.

RESULTS

Ganglionic-receptor-binding antibodies were found in 19 of 46 patients with idiopathic or paraneoplastic autonomic neuropathy (41 percent), in 6 of 67 patients with postural tachycardia syndrome, idiopathic gastrointestinal dysmotility, or diabetic autonomic neuropathy (9 percent), and in none of 44 patients with other autonomic disorders. High levels of the binding antibodies correlated with more severe autonomic dysfunction (including the presence of tonic pupils). Levels of these antibodies decreased in patients who had clinical improvement. All seven patients with ganglionic-receptor-blocking antibodies had ganglionic-receptor-binding antibodies and had idiopathic or paraneoplastic autonomic neuropathy.

CONCLUSIONS

Seropositivity for antibodies that bind to or block ganglionic acetylcholine receptors identifies patients with various forms of autoimmune autonomic neuropathy and distinguishes these disorders from other types of dysautonomia. The positive correlation between high levels of ganglionic-receptor antibodies and the severity of autonomic dysfunction suggests that the antibodies have a pathogenic role in these types of neuropathy.

Antineuronal antibodies in patients with neuroblastoma and paraneoplastic opsoclonus-myoclonus

PURPOSE

To identify serologic markers in children with paraneoplastic opsoclonus-myoclonus (POM).

MATERIALS AND METHODS

We examined the sera of 64 children with neuroblastoma (16 with POM and 48 age-matched and stage-matched controls) by immunohistochemistry of rat brain and human cerebellum, and by Western blot analysis of protein extracts from human Purkinje cells, cortical neurons, neuroblastoma cell lines, and HuD.

RESULTS

Using immunohistochemistry, IgG reactivity against neurons was identified in 13 of 16 POM sera (81%), and 12 of 48 non-POM sera (25%; P<0.001). IgM antineural antibodies were present in 3 of 16 POM sera (19%) and 11 of 48 (23%) non-POM sera. Except for anti-Hu antibodies detected in 10 sera (4 with POM), no other specific reactivities were identified by Western blot analysis of neuronal or of neuroblastoma protein extracts.

CONCLUSIONS

We conclude that: 1) patients with neuroblastoma and POM are more likely to harbor antineuronal antibodies than patients without POM; 2) no specific serologic marker of POM was identified, but the frequent presence of antineuronal antibodies suggests that POM is immune-mediated; and 3) anti-Hu antibodies are present in some sera from patients with neuroblastoma, irrespective of the presence of POM.

Paraneoplastic limbic encephalitis: neurological symptoms, immunological findings and tumour association in 50 patients

Paraneoplastic limbic encephalitis (PLE) is a rare disorder characterized by personality changes, irritability, depression, seizures, memory loss and sometimes dementia. The diagnosis is difficult because clinical markers are often lacking, and symptoms usually precede the diagnosis of cancer or mimic other complications. The frequency of antineuronal antibodies in patients with PLE has not been investigated. We examined the neurological symptoms and the causal tumours in 50 patients with PLE to determine the utility of paraneoplastic antibodies and other tests. The diagnosis of PLE required neuropathological examination or the presence of the four following criteria: (i) a compatible clinical picture; (ii) an interval of <4 years between the development of neurological symptoms and tumour diagnosis; (iii) exclusion of other neuro-oncological complications; and (iv) at least one of the following: CSF with inflammatory changes but negative cytology; MRI demonstrating temporal lobe abnormalities; EEG showing epileptic activity in the temporal lobes. Of 1047 patients with neurological symptoms, whose sera or CSF were examined for paraneoplastic antibodies, 79 had the presumptive diagnosis of limbic encephalitis, dementia, cognitive dysfunction, or confusion. Fifty of these patients fulfilled our criteria for PLE. Pathological confirmation was obtained in 12 patients. The commonly associated neoplasms were of the lung (50%), testis (20%) and breast (8%). Neurological symptoms preceded the cancer diagnosis in 60% of patients (by a median of 3.5 months). Twenty-five of 44 (57%) patients with MRI studies had signal abnormalities in the limbic system. Thirty (60%) patients had antineuronal antibodies (18 anti-Hu, 10 anti-Ta, 2 anti-Ma), and 20 were antibody-negative or had uncharacterized antibodies (n = 4). The combination of symptoms, MRI findings and paraneoplastic antibodies established the diagnosis of PLE in 78% of the patients. Patients with anti-Hu antibodies usually had small-cell lung cancer (94%), multifocal neurological symptoms (78%) and a poor neurological outcome. Patients with anti-Ta (also called anti-Ma2) antibodies were young men with testicular tumours (100%), frequent hypothalamic involvement (70%) and a poor neurological outcome. In the group of patients without anti-Hu or anti-Ta antibodies, the tumour distribution was diverse, with cancer of the lung the most common (36%); 57% had positive MRI. Fifteen of 34 (44%) patients with a median follow-up of 8 months showed neurological improvement. Treatment of the tumour appeared to have more effect on the neurological outcome than the use of immune modulation. Improvement was observed in 38% of anti-Hu patients, 30% of anti-Ta patients and 64% of patients without these antibodies.

Paraneoplastic syndromes: an unsolved murder

With neuroimmunology playing an ever greater role in child neurology, paraneoplastic syndromes--uncommon but often devastating complications of cancer--are in the forefront. Abnormalities of both humoral and cellular immunity support the immunological theory of causation. Through co-complicity of host and tumor factors, targets of immunologically mediated injury remote from the tumor may be damaged or destroyed, giving rise to discrete neurological deficits. In the nervous system, the main targets are neuronal nuclei or cell bodies, structural constituents, surface receptors, synapses, and ion channels. The clinical syndromes and response to treatment differ substantially between children and adults. Current pharmacological and biological therapies, which are nonselective, include noncytotoxic and cytotoxic drugs, intravenous immunoglobulins, plasma exchange, and immunoadsorption, some chosen for induction and others for maintenance. Tumor resection and thymectomy are surgical treatments. Combination immunotherapies allow steroid sparing, targeting of more than one immunologic effector pathway, and deploy an advantageous mixture of early- and late-acting drugs. More selective and efficacious immunotherapies are needed.

Autoantibodies in paraneoplastic neurological syndrome

Paraneoplastic neurological syndrome is a rare disorder caused by the secondary effects of cancer and is thought to be immune-mediated. A high titer of autoantibodies in the patient's serum and cerebrospinal fluid, directed against both neurons and tumor, have been detected in some forms of this syndrome. These autoantibodies are considered the result of an immunological response to tumor and may cross-react with cells of the nervous system, causing neuronal damage. Specific forms of this syndrome are often associated with specific antineuronal antibodies and tumors. The onset of neurological symptoms and detection of these antibodies often precede the diagnosis of the tumor; therefore, detection of these antibodies greatly assists the diagnosis of this syndrome and prompts investigations for the underlying tumor. The pathogenicity of these antineuronal antibodies has been proven in only a few cases, such as that of anti-voltage gated calcium-channel antibodies in Lambert-Eaton myasthenic syndrome. The selective involvement of specific types of neurons has not been fully elucidated. The target spectrum of some of these antineuronal antibodies correlates well with the neurological symptoms, but that of others is wider than expected from the symptoms. Interesting evidence has suggested that these antionconeuronal antibodies can suppress tumor growth. The discovery of new antibodies and characterization of target molecules have been reported with advances in the field of molecular biology. A more detailed understanding of the relationship between the cancer and the neural involvement from the molecular biological standpoint may lead to rational tumor therapy and elucidation of the mechanism of neuronal death. Here, major clinical forms with well-known antineuronal antibodies and specific tumors are reviewed; for each antineuronal antibody, the target antigens and its putative role in the pathogenesis of this syndrome are described.

RNA-binding analyses of HuC and HuD with the VEGF and c-myc 3'-untranslated regions using a novel ELISA-based assay

Human members of the ELAV family, referred to as ELAV-like proteins (ELPs), include HuC, HuD, Hel-N1 and HuR. These proteins bind to AU-rich elements in the 3'-untranslated regions (3'-UTRs) of many growth-related mRNAs, including c-myc and VEGF, and may participate in regulating the stability of these transcripts. Here, I have developed an enzyme-linked immunosorbent assay (ELISA) which can rapidly assess the RNA-protein-binding properties of ELPs. With this assay, I demonstrate that HuC and HuD bind to the VEGF 3'-UTR regulatory segment (VRS) and to the c- myc 3'-UTR in a specific and concentration-dependent pattern, with both proteins showing a greater affinity for the VRS. Further analysis of the VRS indicated that the binding affinity was greater for the 3'-end where the majority of AU motifs reside. Binding to the VRS could be competed by both proteins as well as a poly(U) ribohomopolymer. The binding could not be competed by other ribohomopolymers or serum from patients with high titer anti-HuD antibodies. In summary, this assay provides a rapid analysis of ELP-RNA binding which can be utilized for further characterization of RNA-binding properties and for identification of competitor molecules for in vivo functional analysis of ELPs.

Antibodies to calcium channel and synaptotagmin in Lambert-Eaton myasthenic syndrome

In the Lambert-Eaton myasthenic syndrome (LEMS), an autoimmune disease that is often associated with lung cancer and characterized by reduced quantal release of acetylcholine from the motor nerve terminal, our studies to search for the target of LEMS antibodies have brought the voltage-gated calcium channel (VGCC) into relief. Among multiple types of VGCCs, the P/Q-type was highly recognized by LEMS antibodies. Using synthetic peptides or recombinant proteins as antigens, the study specified the S5-S6 linker regions in 3 of 4 domains as immunodominant sites in the molecular structure of P/Q-type VGCC alpha1 subunit. Synaptotagmin, one of the functionally VGCC-associated synaptic proteins, was also found to be an immunogen in the pathogenesis of LEMS.

[Intrathecal synthesis of the anti-Hu antibody in patients with paraneoplastic encephalomyelitis or sensory neuronopathy]

OBJECTIVE

To probe into the pathogenic mechanisms of paraneoplastic encephalomyelitis (PEM) or sensory neuronopathy(PSN).

METHODS

The serum and cerebral spinal fluid(CSF) anti-Hu antibodies and titers in 16 patients with PEM and 14 patients with PSN were detected with indirect immunohistochemistry (ABC) method. Intrathecal IgG synthesis and antibody specific activity (ASA) were calculated with Schuller's formulas according to the titers of the anti-Hu antibodies in the serum and CSF of the patients. Anti-Hu antibodies were identified by detecting the antigens of the nuclear extracts from the human cerebral cortex neurons with Western blot analysis. IgG in the serum and CSF and the albumin in the CSF were tested with electroimmunodiffusion method.

RESULTS

The serum and CSF anti-Hu antibody titers in patients with PEM were significantly higher than those in patients with PSN (P < 0.001). A ratio of intrathecal ASA/serum ASA of anti-Hu antibody > 2 in 14 (88%) of the 16 patients with PEM and one (7%) patient with PSN indicated that the patients with PEM had a positive intrathecal anti-Hu antibody synthesis (P < 0.001). The Rankin scores are 4.5 +/- 1.7 in patients with PEM and 3.0 +/- 1.4 in patients with PSN (P < 0.01). Patients with PEM were more disabled than those with PSN.

CONCLUSIONS

The detection of intrathecal ASA/serum ASA ratio for identifying the anti-Hu antibody intrathecal synthesis is valuable in judging the severity of disease and prognosis in patients with paraneoplastic syndromes of nervous system.

[Paraneoplastic neurological syndromes: from the diagnosis of exclusion to the use of immunological and molecular markers]

For many years paraneoplastic neurological syndromes have been identified through the exclusion of other neurological complications in patients with cancer. The discovery that many paraneoplastic syndromes are associated with immunological reactions allows a specific and comprehensive definition of these disorders, which often can be promptly recognized by the serological detection of antineuronal antibodies. In a significant number of paraneoplastic syndromes the genes coding for the target onconeuronal antigens have been cloned and their functions are being elucidated. This study reviews the pathogenic mechanisms of paraneoplastic neurological syndromes and addresses the most frequently asked questions regarding their diagnosis and treatment.

[Small cell lung cancer associated with anti-Hu antibody-positive paraneoplastic neurologic syndrome]

We report a case of small cell lung cancer with anti-Hu antibody-positive paraneoplastic neurologic syndrome preceded by variable neurological symptoms. A 57-year-old man first noticed a numbness on the inner side of his right leg in April 1998. He was later admitted to a hospital following the development of polyneuropathy, cerebellar dysfunction, and psychological symptoms. Chest plain X-ray films and computed tomographic scans disclosed a mass shadow in the right upper lobe, in addition to enlarged mediastinal lymph nodes. Small cell lung cancer was suspected on the basis of pathologic findings on an enlarged right supraclavicular lymph node and radiologic findings. The patient was referred to our hospital in October 1998. Anti-Hu antibody was detected both in serum and cerebrospinal fluid. Small cell lung cancer (clinical T1N3M0, stage IIIB) with paraneoplastic neurologic syndrome was diagnosed. Three courses of combination chemotherapy (carboplatin and etoposide) were administered with a partial response. However, the patient's neurological symptoms were not alleviated. We discussed the mechanism, clinical symptoms, and treatment of this disease.

Ulip/CRMP proteins are recognized by autoantibodies in paraneoplastic neurological syndromes

Anti-CV2 autoantibodies have recently been discovered in patients with paraneoplastic neurological diseases (PND). These disorders are associated with neuronal degeneration, mediated by autoimmune processes, in patients with systemic cancer. Anti-CV2 autoantibodies recognize a brain protein of 66 kDa developmentally regulated and specifically expressed by a subpopulation of oligodendrocytes in the adult brain. Here, we demonstrate that anti-CV2 sera recognize several post-translationally modified forms of Ulip4/CRMP3, a member of a protein family related to the axonal guidance and homologous to the Unc-33 gene product in Caenorhabditis elegans. The sequence of the human Ulip4/CRMP3 was determined and the gene localized to chromosome 10q25.2-q26, a region mutated in glioblastomas and containing tumour suppressor genes. The identification of the Ulip/CRMP proteins as recognized by anti-CV2 sera should provide new insights into the role of Ulip/CRMPs in oligodendrocytes and into pathophysiology of PND.

Hu antigen specificities of ANNA-I autoantibodies in paraneoplastic neurological disease

Despite a broad clinical spectrum, paraneoplastic enecephalomyelitis/sensory neuronopathy (PEM/SSN) is characterized by the presence of a common autoantibody, referred to as anti-Hu or type I anti-neuronal nuclear antibody (ANNA-1). The target of these antibodies is a family of four Hu antigens: three (Hel-N1, HuC, HuD) are neural-specific, while the fourth (HuR) is ubiquitous. Here, we have analysed by enzyme-linked immunosorbent assay (ELISA) the immunoreactivity of all four Hu antigens in serum from 75 patients with ANNA-1 autoantibodies and looked for clinical correlations. IgG in all the patients' sera bound to each of the four antigens, and the titers correlated with those of the ANNA-I immunofluorescence assay. Median titers for the neural-specific antigens (range: 56, 892-90,051) were significantly higher than for HuR (36,799). Patients with gastrointestinal dysmotility or subacute sensory neuronopathy had the highest median titers to all four antigens, while patients with sensorineural deafness had the lowest titers. The results indicate a heterogeneous immune response to individual Hu antigens in patients with PEM/SSN, and that the titers to these antigens as a group, rather than individually, correlate with clinical profile. Furthermore, these results suggest that ELISA analysis of a single neural-specific Hu antigen is sufficient for serological screening in PEM/SSN.

[Paraneoplastic neurologic syndromes. Diagnostic and pathogenetic significance of autoantibodies]

Paraneoplastic neurologic syndromes (PNS) are rare disorders of the nervous system that cannot be ascribed to metastases or to destruction of vital systemic organs by the tumor or its treatment. Most frequently, PNS occur in association with small-cell lung, breast or ovarian carcinomas. The most frequent PNS is Lambert-Eaton myasthenic syndrome, which at the same time has the highest predictive value concerning an underlying carcinoma. PNS have been classified mostly under anatomical aspects but now are increasingly categorized according to specific antibodies. In certain neurologic syndromes (sensible and autonomic neuropathy, cerebellitis, limbic encephalitis, Opsoclonus-Myoclonus syndrome, Stiff-man syndrome, neuromyotonia, subacute amaurosis) specific autoantibodies are highly predictive for a neoplasm. Pathogenic relevance of these autoantibodies has been demonstrated only for antibodies against (1) voltage gated calcium channels (VGCC) in Lambert-Eaton myasthenic syndrome, (2) voltage gated potassium channels (VGKC) in neuromyotonia, and (3) recoverin in cancer associated retinopathy. The present article deals with the neurological symptoms of PNS, associated tumors, and the relevance of specific antibodies for the diagnosis and pathogenesis of PNS.