Analysis of autoantibody binding to 52-kd paraneoplastic cerebellar degeneration-associated antigen expressed in recombinant proteins

Changing landscape in the field of paraneoplastic neurology: Personal perspectives over a 35-year career

Paraneoplastic neurologic syndromes are a group of rare disorders that have fascinated neurologists for more than a century. The discovery in the 1980s that many of these disorders occurred in association with antibodies against neuronal proteins revived the interest for these diseases. This chapter first traces the history of the paraneoplastic neurologic syndromes during the era that preceded the discovery of immune mechanisms and then reviews the immunologic period during which many of these syndromes were found to be associated with antibodies against intracellular onconeuronal proteins and pathogenic cytotoxic T-cell mechanisms. Alongside these developments, investigations on the antibody-mediated disorders of the peripheral nervous system, such as the myasthenic syndromes or neuromyotonia, provided suggestions for the study of the central nervous system (CNS) syndromes. These converging areas of research culminated with the groundbreaking discovery of a new category of CNS disorders mediated by antibodies against neuronal surface proteins or receptors. These disorders are not always paraneoplastic, and the understanding of these syndromes and mechanisms has changed the landscape of neurology and neurosciences.

Paraneoplastic motor disorders

Paraneoplastic neurological disorders (PNDs) are heterogeneous clinicopathologic syndromes that occur throughout the neuraxis resulting from damage to organs or tissues remote from the site of a malignant neoplasm or its metastases. The discordance between severe neurological disability and even an indolent malignancy suggests an underlying neuroimmunologic host immune response that inflicts nervous tissue damage while inhibiting malignant tumor growth. Motor system involvement, like other symptoms and signs, is associated with focal or diffuse involvement of the brain, spinal cord, peripheral nerve, neuromuscular junction or muscle, alone or in combination due to an underlying neuroimmune and neuroinflammatory process targeting neural-specific antigens. Unrecognized and therefore untreated, PNDs are often lethal making early detection and aggressive treatment of paramount importance. While the combination of clinical symptoms and signs, and analysis of detailed body and neuroimaging, clinical neurophysiology and electrodiagnostic studies, and tumor and nervous system tissue biopsies are all vitally important, the certain diagnosis of a PND rests with the discovery of a corresponding neural-specific paraneoplastic autoantibody in the blood and/or spinal cerebrospinal fluid.

Anti-Yo positive paraneoplastic cerebellar degeneration: a report of three cases and review of the literature

Anti-Yo is an anti-Purkiney cell cytoplasmic antibody found in approximately 50% of patients with parancoplastic cerebellar degeneration (PCD). We report three patients with anti-Yo positive PCD (one ovarian carcinoma and two poorly differentiated adenocarcinomas consistent with breast origin). Two were treated with chemotherapy and plasmapheresis but died within months of the diagnosis from progressive neurological disease. The other was given gamma-globulin and has remained table at 6 months follow up. Anti-Yo antibodies are highly specific with almost all patients having breast or gynaecological malignanies. Commonly the tumour is of small volume and asymptomatic. Attempts at treatment are usually unsuccessful but there are a number of reports of stabilisation or improvement when treatment is begun before the development of severe neurological disability. The detection of anti-Yo antibodies is very useful for the diagnosis of PCD allowing early tumour detection and prompt institution of treatment.

Antineuronal autoantibodies in neurological disorders

Autoantibodies (abs) related to neurological disease are currently classified into two large groups depending on the site of the respective target antigen: Group I encompasses abs that recognise intracellular antigens (Hu, Yo, Ri, CV2/CRMP5, amphiphysin, Ma2, SOX, ZIC, GAD, adenylate kinase 5, homer 3), whereas group II abs are targeted against neuronal cell membrane antigens (VGKC, AMPA-R, GABAB-R, NMDA-R, Glycine-R, VGCC, metabotropic GluR1). Both abs groups can be further subdivided according to their diagnostic impact for paraneoplastic or non-paraneoplastic neurological disease. The review gives an overview of the common characteristics of each group and provides more detailed information on single abs and the associated clinical syndromes.

Purkinje cell death after uptake of anti-Yo antibodies in cerebellar slice cultures

Paraneoplastic cerebellar degeneration accompanying gynecological and breast cancers is characteristically accompanied by a serum and cerebrospinal fluid (CSF) antibody response, termed "anti-Yo," which reacts with cytoplasmic proteins of cerebellar Purkinje cells. Because these antibodies interact with cytoplasmic rather than cell surface membrane proteins, their role in causing Purkinje cell death has been questioned. To address this issue, we studied the interaction of anti-Yo antibodies with Purkinje cells in slice (organotypic) cultures of rat cerebellum. We incubated cultures with immunoglobulin G (IgG)-containing anti-Yo antibodies using titers of anti-Yo antibody equivalent to those found in CSF of affected patients. Cultures were then studied in real time and after fixation for potential uptake of antibody and induction of cell death. Anti-Yo antibodies delivered in serum, CSF, or purified IgG were taken up by viable Purkinje cells, accumulated intracellularly, and were associated with cell death. Normal IgG was also taken up by Purkinje cells but did not accumulate and did not affect cell viability. These findings indicate that autoantibodies directed against intracellular Purkinje cell proteins can be taken up to cause cell death and suggest that anti-Yo antibody may be directly involved in the pathogenesis of paraneoplastic cerebellar degeneration.

Anti-Ri-associated paraneoplastic cerebellar degeneration and breast cancer: an autopsy case study

Several antineuronal antibodies are associated with paraneoplastic cerebellar degeneration. Anti-Ri is one of these antibodies in some cases but it is more commonly associated with paraneoplastic opsoclonus myoclonus in the context of gynecological neoplasia. Anti-Ri autoantibodies are thought to be directed against onconeural antigens, NOVA-1 and NOVA-2, that are expressed by the tumor as well as by neurons. The results of the treatment of both syndromes have been disappointing, although aggressive multimodality immunosuppressive treatments have been used. There are few cases of anti-Ri paraneoplastic cerebellar degeneration and none has been pathologically studied. We report the pathological study of a patient who died from anti-Ri-positive paraneoplastic cerebellar degeneration associated with breast cancer only confirmed at autopsy.

Yo antibodies in ovarian and breast cancer patients detected by a sensitive immunoprecipitation technique

Onconeural antibodies are found in patients with cancer and are associated with paraneoplastic neurological syndromes (PNS). The objective of the present study was to assess the frequency of Yo antibodies in ovarian and breast cancer using a sensitive immunoprecipitation technique, and to look for any association of Yo antibodies with neurological symptoms and prognostic factors. A multiwell adapted fluid-phase immunoassay using radiolabelled recombinant cerebellar degeneration related protein (cdr2), produced by coupled in vitro transcription/translation was used for the detection of Yo antibodies. This technique combines high specificity and sensitivity with high sample analysing capacity for the antibody in question. Sera or EDTA-blood from 810 ovarian (n = 557) and breast cancer (n = 253) patients were analysed for Yo antibodies by immunoprecipitation, as well as immunofluorescence and immune blots. Two hundred healthy blood donors and sera from 17 patients with paraneoplastic cerebellar degeneration and Yo antibodies served as controls. Immunoprecipitation was more sensitive in detecting Yo antibodies than immunofluorescence and immune blots. The prevalence of Yo antibodies was 13/557 (2.3%) in ovarian cancer and 4/253 (1.6%) in breast cancer using immunoprecipitation. Yo antibodies were not correlated with specific histological subgroups. The Yo index of ovarian cancer patients in FIGO stage IV was higher compared to FIGO stage I-III. The prevalence of Yo antibodies was 3 times higher in patients with stage III breast cancer than in stage I and II. Only 2/17 (11.8%) patients with Yo antibodies detected during the screen of 810 cancer patients had PNS. The results show that the prevalence of Yo antibodies is low in ovarian and breast cancer. Yo antibodies may be associated with advanced cancer, but less often with PNS.

Induction of humoral responses specific for paraneoplastic cerebellar degeneration-associated antigen by whole recombinant yeast immunization

Paraneoplastic cerebellar degeneration (PCD) is a potent autoimmune disorder in which antigen-driven responses toward the onconeural antigen are assumed to occur in patients. Yeast cell wall has adjuvant capacity and provides immunostimulatory effects of the antigen expressing in viable cells. The recombinant yeast expressing the PCD-associated antigen may become an immunogen for inducing PCD-associated autoimmunity in mice. We attempted to induce autoimmune responses with whole recombinant yeast expressing PCD-associated antigen. SJL/J strain of mouse is found to be a responder to the major epitope on the antigen for anti-Purkinje cell antibodies, and whole recombinant yeast could induce cellular and humoral autoimmune responses in vivo ion SJL/J mice. The immunization technique based on the recombinant yeast expressing a PCD-associated antigen provides a new tool for analyzing the underlying immunological pathomechanisms of PCD.

Neuroimmunology of the paraneoplastic neurological degenerations

The paraneoplastic neurological degenerations (PNDs) are remarkable examples of naturally occurring tumor immunity in humans. In PND patients, common tumors such as breast, ovarian and lung tumors express proteins normally made exclusively in the brain, eliciting an immune response that successfully suppresses growth of the tumor. This successful anti-tumor response would be expected to go clinically unnoticed by the patient, but the immune cells mediating the response somehow cross into the brain, resulting in an autoimmune attack on neurons and neurological symptoms. Pieces of the mystery of this tumor immune response and neuronal autoimmunity have been assembled, but much more needs to be learned.

Effect of a paraneoplastic cerebellar degeneration-associated neural protein on B-myb promoter activity

In this study, we have shown that a paraneoplastic cerebellar degeneration (PCD)-associated antigen, pcd17, binds to a cell cycle-related protein, MRG15. MRG15 derepresses the E2F-responsive B-myb promoter. The pcd17 antigen inhibits the derepression of the B-myb transcriptional activity by MRG15, and, as a result, pcd17 represses the promoter. Delivery of anti-Purkinje cell antibodies (anti-Yo) into the cells inhibits the repression of B-myb promoter activity by pcd17. Because derepression of the B-myb promoter has been implicated in neuronal death, the results suggest the possible role of the antibodies in the pathogenesis of PCD.

Effects of antineuronal antibodies from patients with paraneoplastic neurological syndrome on primary-cultured neurons

Some patients with paraneoplastic neurological syndrome (PNS) produce autoantibodies against tumor and neuronal tissues of symptom-relevant areas. These characteristic antibodies are detected at early stages of the neurological disorder and are reliable markers for the diagnosis of PNS and underlying cancers. These antibodies are thought to be related directly to neuronal damage. However, the passive transfer of antibodies to rodents has been succeeded only in those in which the target antigens were expressed on the cell surface, like Lambert-Eaton myasthenic syndrome. The serum IgGs from patients with PNS and anti-Yo or anti-Hu antibody were not shown to induce the disease by passive transfer or active immunization with these antigen proteins to date. Instead, cytotoxic T lymphocytes (CTLs) against these antigen peptides-presenting targets could be induced in the peripheral blood of PNS patients. However, there is no direct proof of CTLs killing neurons. In this study, we examined the effects of the anti-Yo or anti-Hu antibody on mouse-brain-derived neurons in a primary culture system and found that these antibodies did not kill neurons, but induced the expression of cell adhesion molecules and accelerated neuronal differentiation. These effects of serum IgG fractions containing the anti-Yo or the anti-Hu antibody on the cultured neurons were the same, suggesting that their effects were not through the binding of the antibody to specific antigens, but to some other factors contained in IgG fractions.

Anti-Hu paraneoplastic syndrome presenting with brainstem-cerebellar symptoms and Lambert-Eaton myasthenic syndrome

Paraneoplastic syndrome (PNS) with two distinct neurological features was reported in a 50-year-old man who presented initially with vertigo, ataxia, dysarthria, tremor, confusion, urinary retention and hypotension. Pulmonary X-ray findings, class IIIb sputum cytology, and positive anti-Hu antibody established the diagnosis of PNS associated with small-cell lung cancer (SCLC). Two cycles of combined chemotherapy resulted in shrinkage of the lung tumor together with complete recovery of neurological symptoms and disappearance of anti-Hu antibody. Relapse of SCLC 4 months later with re-appearance of anti-Hu antibody required additional chemotherapy and irradiation. Eight months later, when multiple liver metastasis of SCLC was noticed, muscular weakness with positive waxing phenomenon compatible with Lambert-Eaton myasthenic syndrome (LEMS) developed. Postmortem examinations revealed residual SCLC in the primary lung, and massive liver metastasis with generalized lymph node involvement, but no tumors in the CNS. In the cerebellum, there was a slight loss of Purkinje cells with torpedo formation but without apparent lymphocytic infiltration. The present PNS was unique in that the relapse of SCLC was accompanied by the appearance of anti-Hu antibody, and that initial signs of brainstem-cerebellar symptoms, encephalopathy and autonomic failure were replaced by LEMS coinciding with the tumor recurrence.

Interaction of a paraneoplastic cerebellar degeneration-associated neuronal protein with the nuclear helix-loop-helix leucine zipper protein MRG X

Paraneoplastic cerebellar degeneration-associated antigen PCD17/cdr2 is a neuronal protein expressed predominantly in the cytoplasm of cerebellar Purkinje cells. The biological activities of this protein are not known; however, the presence of a leucine zipper motif in its amino acid sequence suggests that this protein might interact with other proteins harboring a leucine zipper motif. In this study we found by means of a yeast two-hybrid system, ligand overlay assay, and co-immunoprecipitation assay that PCD17 interacts with a nuclear helix-loop-helix leucine zipper protein, MRG X. Overexpression of MRG X in T98G glioblastoma cells by transfection caused abnormal morphological changes in the nucleus and induced cell death. On the other hand, coexpression of PCD17 with MRG X prevented nuclear morphological changes and cell death in T98G cells. MRG X, which is thought to be functionally related to the cell cycle and cell growth, may be regulated by PCD17/cdr2 in Purkinje cells.

Induction of cytotoxic T lymphocytes specific for paraneoplastic cerebellar degeneration-associated antigen in vivo by DNA immunization

Paraneoplastic cerebellar degeneration associated with gynecological and breast malignancies (PCD) is known to develop autoantibodies and autoreactive cytotoxic T lymphocytes (CTLs) specific for a cytoplasmic protein of Purkinje cells PCD17/cdr2, in the blood of patients. The functional roles of these antibodies and CTLs in the pathogenesis of PCD are unknown. Induction of immune response to this antigen in experimental animals should be useful to clarify the immune mechanisms in PCD patients. We immunized Balb/c mice with naked DNA, which is encoded human PCD17 neural protein in an eukaryotic expression plasmid under control of CMV promoter, and explored whether or not humoral and cell-mediated immune responses against PCD17 could be induced in vivo. We show that DNA immunization with naked pcd17 cDNA could induce autoantibodies against the cytoplasmic protein of Purkinje cells and CTLs could lyse syngenic myeloma cells pulsed with H-2K-restricted PCD17 peptide. In spite of the generation of anti-Purkinje cell antibodies and PCD17-specific CTLs in vivo, neither clinical nor pathological changes consistent with significant cerebellar degeneration have been detected.

Paraneoplastic neurologic disease antigens: RNA-binding proteins and signaling proteins in neuronal degeneration

Studies of the disorders known as paraneoplastic neurologic degenerations exemplify the successful application of modern molecular biological techniques to diseases, yielding, even for these extremely rare disorders, wide-ranging insight into basic neurobiology, tumor immunity, and autoimmune neurologic disease. Immune responses to paraneoplastic neurologic degeneration antigens, also called onconeural antigens, have been exploited to clone and characterize a number of neuron-specific proteins, including several RNA-binding proteins and new kinds of signaling molecules. The biology and functions of these proteins are reviewed, and a model in which their functions are related to the pathogenesis of autoimmune neurologic disease is discussed.

Suppression of the transcriptional activity and DNA binding of nuclear factor-kappa B by a paraneoplastic cerebellar degeneration-associated antigen

Paraneoplastic cerebellar degeneration (PCD) associated with gynecological malignancies is a disorder in which an autoimmune mechanism has been suggested, and both antibody- and cell-mediated immune responses exist against pcd17/cdr2, a neural protein expressed in cerebellar Purkinje neurons and brainstem neurons. In this report, we describe that pcd17 can suppress the basal or activated NF-kappaB-dependent transcriptional activity in a co-transfection study. The DNA binding of constitutive NF-kappaB complexes decreased in the nucleus of TNF-alpha-stimulated neuroblastoma cells, though pcd17 does not bind to classical NF-kappaB consensus site. These data indicate that pcd17 is a potential repressor for NF-kappaB-dependent gene transcription in neurons.

Autoantibodies in childhood post-varicella acute cerebellar ataxia

BACKGROUND

Anti-Purkinje cell antibodies have been reported in cerebellar ataxia following Epstein-Barr virus (EBV) infection. We investigated autoantibody responses, including anti-Purkinje cell antibodies, and the clinical course in eight children who developed post-varicella ataxia, five of their siblings with uncomplicated varicella, one child with post-EBV ataxia, two children with acute disseminated encephalomyelitis (ADEM) and one with neuroblastoma associated ataxia, and in age and gender matched controls.

METHODS

Autoantibodies were tested by indirect immunofluorescence (IIF) on cryopreserved cerebrum and cerebellum sections. Other autoantibodies were measured by conventional IIF protocols using HEp-2 cells as a substrate. Antibodies to myelin associated glycoprotein (MAG), asialo-GM1, beta2 glycoprotein 1, cardiolipin and myelin basic protein (MBP) were measured by ELISA.

RESULTS

Three of eight children with acute post-varicella ataxia, one child with post-EBV ataxia, one child with ADEM and one child with uncomplicated varicella, had high titer autoantibodies (>1/160) that reacted with cerebrum and cerebellar tissue. This reactivity was not seen in one child with ADEM, in one with neuroblastoma and ataxia, in the remainder of the children with uncomplicated varicella or age and gender matched controls. Autoantibodies were not seen in CSF from two children with post-varicella ataxia. The punctate staining seen on cerebrum and cerebellum sections co-localized with rabbit antibodies to the centrosome protein pericentrin. All patients with strong reactivity with cerebrum and cerebellar tissue by IIF had elevated levels of anti-MAG that was not confirmed by absorption assay. No reactivity was seen with asialo-GM1, MBP, beta2 glycoprotein 1 or cardiolipin. None of the sera had autoantibodies directed against endosomes, the Golgi complex, or the paraneoplastic autoantigens Hu and Yo.

CONCLUSION

Some children with post-viral ataxia develop antibodies that have strong reactivity with cerebral and cerebellar tissue. Some of the antigenic reactivity co-localized with the centrosome protein pericentrin.

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.

The cytoplasmic Purkinje onconeural antigen cdr2 down-regulates c-Myc function: implications for neuronal and tumor cell survival

Paraneoplastic cerebellar degeneration (PCD) is a disorder in which breast or ovarian tumors express an onconeural antigen termed cdr2, which normally is expressed in cerebellar Purkinje neurons. This leads to an immune response to cdr2 that is associated with tumor immunity and autoimmune cerebellar degeneration. We have found that cdr2, a cytoplasmic protein harboring a helix-leucine zipper (HLZ) motif, interacts specifically with the HLZ motif of c-Myc. Both proteins colocalize in the cytoplasm of adult cerebellar Purkinje neurons, and coimmunoprecipitate from tumor cell lines and cerebellar extracts. cdr2 down-regulates c-Myc-dependent transcription in cotransfection assays, and redistributes Myc protein in the cytoplasm. Disease antisera from six of six PCD patients specifically blocked the interaction between cdr2 and c-Myc in vitro. These data indicate that cdr2 normally sequesters c-Myc in the neuronal cytoplasm, thereby down-regulating c-Myc activity, and suggest a mechanism whereby inhibition of cdr2 function by autoantibodies in PCD may contribute to Purkinje neuronal death.

Antibody recognition and RNA binding of a neuronal nuclear autoantigen associated with paraneoplastic neurological syndromes and small cell lung carcinoma

The PLE21/HuC neural protein is an autoantigen for anti-neuronal nuclear autoantibodies (ANNA-1/anti-Hu/Type IIa antibodies) from a patient with paraneoplastic limbic encephalomyelitis and small cell lung carcinoma. This antigen belongs to the Hu/ELAV-like protein family, contains three RNA recognition motifs (RRMs) and has RNA binding capacity. In many autoimmune diseases mediated by autoantibodies, antibodies often interfere with the biological functions of their target antigens. To investigate the influences of the autoantibodies on the biological function of the antigen, we mapped the regions which were required for the antibody recognition and for the RNA binding. Deletion analysis of the antigen revealed that the epitopes for the antibodies were localized in the regions of 12 residues, amino acids 161-172, and eight residues, amino acids 29-38, of the first and second RRMs. It was also shown that the eight residues, amino acids 29-38, and the 10 residues, amino acids 187-194, were required for the RNA binding. Although amino acids 29-38 were necessary for both the antibody recognition and the RNA bindings, pre-incubation of the PLE21 antigen with the antibodies did not inhibit the formation of the complex of PLE21, the antibodies and RNA. Thus, the regions required for the antibody recognition are not identical with those for the RNA binding, and it seems unlikely that the autoantibodies interfere with RNA binding of the antigen.

PKN interacts with a paraneoplastic cerebellar degeneration-associated antigen, which is a potential transcription factor

PKN is a fatty acid-activated serine/threonine protein kinase, having a catalytic domain homologous to protein kinase C family. PKN has been recently reported to interact with a small GTP-binding protein Rho and cytoskeletal proteins such as neurofilament and alpha-actinin. To identify the new components of the PKN-signaling pathway, the yeast two-hybrid system was employed. Using the amino-terminal regulatory domain of PKN as a bait, cDNA encoding a neural antigen PCD17, which is recognized by characteristic antibodies of patients with paraneoplastic cerebellar degeneration, was isolated from a human brain cDNA library. The interaction between PKN and PCD17 was also determined by the in vitro binding analysis. PCD17 was coimmunoprecipitated with PKN from the lysate of COS7 cells transfected with both expression constructs for PKN and the amino-terminal region of PCD17. PCD17 was phosphorylated by PKN, and the extent of this phosphorylation was enhanced by addition of 40 microM arachidonic acid. The amino-terminal region of PCD17 could form a homodimer in vitro, and PCD17 fused to the Gal4 DNA binding domain showed the transcriptional transactivation of the chloramphenicol acetyltransferase reporter gene linked to 5 Gal4 binding sites and minimal promoter in rat C6 glioma cells. These results suggest the participation of PCD17 in gene expression and lead to a clue for elucidating the PKN signaling pathway from the cytosol to the nucleus.

Neurologic paraneoplastic syndromes

Several neurologic paraneoplastic disorders are believed to be caused by an autoimmune reaction against antigen(s) co-expressed by tumour cells and neurons. Of the paraneoplastic syndromes, the evidence for an autoimmune etiology is strongest for the Lambert-Eaton myasthenic syndrome, in which autoantibodies downregulate voltage-gated calcium channels at the presynaptic nerve terminal. For other syndromes, including cerebellar degeneration, multifocal encephalomyelitis, sensory neuronopathy, limbic encephalitis, opsoclonus-myoclonus, stiff person syndrome, and retinal degeneration, the autoimmune theory is supported by the presence of specific antineuronal antibodies. These antibodies serve as a useful diagnostic tool, but their actual role in causing neuronal injury and clinical disease remains unclear. Further understanding of immunopathogenesis awaits successful experimental models. Among different syndromes, a varied proportion of patients shows neurologic improvement with immunosuppressive treatments; it is likely that many patients have already suffered irreversible neuronal injury at the time of diagnosis.

A post-transcriptional regulatory mechanism restricts expression of the paraneoplastic cerebellar degeneration antigen cdr2 to immune privileged tissues

Paraneoplastic cerebellar degeneration (PCD) is believed to be an autoimmune disorder initiated by the ectopic expression of a neuron-specific protein in breast and ovarian tumors. PCD antisera was used previously to identify several cerebellar degeneration-related (cdr) genes encoding putative PCD antigens. We have found that the cdr2 gene, which encodes a cytoplasmic leucine zipper protein of unknown function, is expressed in PCD-associated tumors, whereas other cdr genes are not; thus, cdr2 encodes the PCD tumor antigen. To determine whether the expression pattern of cdr2 is consistent with its proposed role in PCD, we have isolated the mouse homolog and examined both the mRNA and protein distribution in adult tissues. We have found that cdr2 mRNA is expressed in almost all tissues, whereas the protein is expressed only in the brain and testis. Within the brain, both the cdr2 mRNA and immunoreactivity are confined primarily to neurons in the cerebellum and brainstem, the regions most affected in PCD. These results suggest first that the tissue-specific expression of cdr2 is regulated at a post-transcriptional level. Moreover, because the brain and testis are considered to be immune-privileged sites, the expression pattern of cdr2 is compatible with the autoimmune model of PCD pathogenesis.

Autoimmunity to ion-channels and other proteins in paraneoplastic disorders

Paraneoplastic neurological disorders are rare conditions caused by immune responses against tumour antigens that cross-react with neuronal antigens. In the past year, there have been advances in the definition of some of the antigens that are recognized by patients' antibodies, and new observations on the results of passive and active immunization against the antigens.

Onconeural antigens and the paraneoplastic neurologic disorders: at the intersection of cancer, immunity, and the brain

Paraneoplastic neurologic disorders (PNDs) are believed to be autoimmune neuronal degenerations that develop in some patients with systemic cancer. A series of genes encoding previously undiscovered neuronal proteins have been cloned using antiserum from PND patients. Identification of these onconeural antigens suggests a reclassification of the disorders into four groups: those in which neuromuscular junction proteins, nerve terminal/vesicle-associated proteins, neuronal RNA binding proteins, or neuronal signal-transduction proteins serve as target antigens. This review considers insights into basic neurobiology, tumor immunology, and autoimmune neuronal degeneration offered by the characterization of the onconeural antigens.

Expression of messenger RNA encoding a paraneoplastic cerebellar degeneration-associated antigen in the rat hippocampus

The PCD17 protein is a paraneoplastic cerebellar degeneration (PCD)-associated neural autoantigen which is recognized by autoantibodies in sera of PCD patients. The localization of the PCD17 mRNA was examined by in situ hybridization histochemistry using a PCD17 cRNA probe. In the cerebellum, the localization of the transcript was in agreement with the distribution of PCD17-immunoreactivity. On the other hand, intense hybridization signals were detected in most of cells in the hippocampus in which notable PCD17-immunoreactivity was undetected. These observations suggest that some negative translational or post-transcriptional mechanisms of the PCD17 mRNA may be involved in neurons of the hippocampus.

Induction of anti-Purkinje cell antibodies in vivo by immunizing with a recombinant 52-kDa paraneoplastic cerebellar degeneration-associated protein

We immunized five different strains of mice with the recombinant human PCD17 protein, which is recognized by anti-Purkinje cell antibodies in the sera of patients with paraneoplastic cerebellar degeneration, and explored whether or not antibodies against cerebellar Purkinje cells could be induced in vivo. Autoantibodies against the cytoplasmic protein of Purkinje cells and other neurons were raised in all the strains of mice. These antisera stained the cytoplasm of cytoplasm of the Purkinje cell in a coarse, granular pattern, but spared the nucleus. The antisera did not stain cerebellar granular cells. This pattern of immunostaining seen with the mouse antisera is similar to that seen with the human PCD sera, but more widespread cells in the central nervous system were stained with these antisera. The titers of the induced antibodies were comparable to or even higher than those of humans. The deposition of IgG was also demonstrated in the cytoplasm of Purkinje cells in the immunized mice. In spite of the generation of anti-Purkinje cell antibodies in vivo, neither clinical nor pathological changes consistent with cerebellar degeneration were detected 1 year following the first immunization.

Autoimmune central nervous system paraneoplastic disorders: mechanisms, diagnosis, and therapeutic options

The presence of specific antineuronal antibodies in some patients with paraneoplastic central nervous system (CNS) disorders supports the theory that these syndromes have an autoimmune etiology. The anti-Purkinje cell antibodies (APCAs) in some patients with paraneoplastic cerebellar degeneration and ovarian or breast carcinomas stain the cytoplasm of Purkinje cells. APCAs react with several distinct neuronal protein autoantigens, including proteins featuring a "leucine zipper" sequence motif, which suggests that they function in regulating DNA transcription. Type 1 anti-neuronal nuclear antibodies (ANNA-1) associated with paraneoplastic encephalomyelitis and small-cell lung carcinoma stain the nucleus and cytoplasm of all neurons, and react with a group of 35- to 40-kd proteins in neuronal immunoblots. The protein targets of ANNA-1 belong to a family of RNA-binding proteins that probably regulate posttranscriptional processing of RNA. Type 2 anti-neuronal nuclear antibodies (ANNA-2) associated with paraneoplastic opsoclonus-ataxia and breast carcinoma also produce a panneuronal immunocytochemical staining pattern, but react with a group of higher-molecular-mass proteins (53-61 kd and 79-84 kd); these autoantigens probably also function as RNA-binding proteins. Several patients with paraneoplastic stiff-man syndrome have antibodies against a 128-kd synaptic protein. These antineuronal antibodies are highly specific (but not infallible) diagnostic markers for the presence of a neoplasm in patients who present with neurological dysfunction. The actual role of these autoantibodies in the pathogenesis of neuronal damage and clinical disease remains to be determined. Current management options for patients with CNS neurological paraneoplastic syndromes are very limited. Only a small minority of patients with paraneoplastic cerebellar degeneration or encephalomyelitis show significant neurological improvement after successful tumor treatment and/or immunosuppressive treatments, while patients with paraneoplastic opsoclonus or stiff-man syndrome have a somewhat better outlook.

Long term course of change in anti-Yo antibody content in paraneoplastic cerebellar degeneration

Images

Trial to establish an animal model of paraneoplastic cerebellar degeneration with anti-Yo antibody. 2. Passive transfer of murine mononuclear cells activated with recombinant Yo protein to paraneoplastic cerebellar degeneration lymphocytes in severe combined immunodeficiency mice

Passive transfer of serum IgG or mononuclear cells from peripheral blood of a patient with paraneoplastic cerebellar degeneration (PCD) to rodents was carried out in order to examine the role of anti-Purkinje cell antibody (anti-Yo antibody) present in serum and cerebrospinal fluid of PCD patients. After a single injection of IgG into mouse brain, it was taken up by Purkinje cells and remained there for more than 36 h without Purkinje cell loss. Injection of PCD IgG together with complement or lipopolysaccharide-activated human macrophages or rat mononuclear cells into rat ventricles did not cause Purkinje cell loss. We also studied passive transfer of the PCD patient's lymphocytes to mice with severe combined immunodeficiency (SCID). We constructed a recombinant Yo fusion protein that has the leucine-zipper protein (Yo protein), the common epitope for anti-Yo antibody for immunizing mice, and that resulted in production of significant amounts of anti-Yo antibody. Spleen cells from these Yo protein immunized mice were injected intravenously or intracerebrally into naive mice that subsequently showed no neurological symptoms or loss of Purkinje cells. We conclude that the anti-Yo antibody, either in combination with or without complement or activated mononuclear cells, cannot be the sole cause of Purkinje cell loss.

Trial to establish an animal model of paraneoplastic cerebellar degeneration with anti-Yo antibody. 1. Mouse strains bearing different MHC molecules produce antibodies on immunization with recombinant Yo protein, but do not cause Purkinje cell loss

Passive transfer of anti-Yo antibody from patients with paraneoplastic cerebellar degeneration (PCD) associated with gynecological or breast carcinoma has not been successful in inducing an animal model. We used active immunization with recombinant Yo protein of four strains of mice bearing different MHC molecules: BALB/c (H-2d), C3H (H-2k), C57BL/6 (H-2b), SJL/J (H-2s). All the strains produced high anti-Yo antibody titer but none developed cerebellar ataxia or showed Purkinje cell loss. Spleen cells from the immunized mice also reacted with recombinant protein. Because C57BL/6(nu/nu) mice produce no anti-Yo antibody, mature helper T cells are required for its production. Results suggest that antibody production in peripheral blood alone is not sufficient for the development of PCD and that MHC class II molecules function in the activation of T cells to help B cells to help B cells produce antibodies.

Passive transfer and active immunization with the recombinant leucine-zipper (Yo) protein as an attempt to establish an animal model of paraneoplastic cerebellar degeneration

Passive transfer of paraneoplastic cerebellar degeneration (PCD) IgG to rodents as well as active immunization with recombinant Yo fusion protein were tried in order to examine the roles of anti-Purkinje cell antibody (anti-Yo antibody) present in the sera and cerebrospinal fluid of patients with PCD in Purkinje cell loss, the hall mark of PCD pathology. On a single injection of PCD IgG to mouse brain, IgG was taken into Purkinje cells and remained there for more than 36 h without Purkinje cell loss. Injection of PCD IgG together with complement or lipopolysaccharide-activated human macrophages or rat mononuclear cells to rats ventricles did not cause Purkinje cell loss. We made a recombinant Yo fusion protein that has the leucine-zipper protein (Yo protein), the common epitope for anti-Yo antibody. Mice immunized with this Yo protein produced high titer antibody against it for more than 3 months, during which time neither neurological symptoms nor Purkinje cell loss occurred. The anti-Yo antibody, with or without complement or activated mononuclear cells, therefore could not be the sole cause of Purkinje cell loss.