A novel neuronal antigen identified by sera from patients with systemic lupus erythematosus

Identification of autoantigens specific for systemic lupus erythematosus with central nervous system involvement

Using proteomic analysis, we identified candidate autoantigens specific for central nervous system (CNS) involvement in systemic lupus erythematosus (SLE). Proteins, extracted from cultured human neuroblastoma cells, were separated both by SDS-PAGE (1-DE) and two-dimensional electrophoresis (2-DE), and transferred to membranes. Western blot analysis was performed using serum samples from 30 SLE patients with CNS involvement (CNS-Lupus) and from 30 SLE patients without CNS involvement (non-CNS-SLE). The detected autoantigens were identified using MALDI-TOF/TOF MS. On the 1-DE Western blot, we detected 32 antigenic bands in the serum samples from the CNS-Lupus patients. Among them, four bands were detected significantly more frequently in the CNS-Lupus patients than in the non-CNS-SLE patients. Three bands were detected in four or more of the CNS-Lupus patients but in only one or none of the non-CNS-SLE patients. We thus selected these seven bands for the next investigations. Next, we detected protein spots corresponding to the selected seven bands by 2-DE Western blot and identified four proteins. They are peroxiredoxin-4, ubiquitin carboxyl-terminal hydrolase isozyme L1, splicing factor arginine/serine-rich 3, and histone H2A type 1. These four candidate autoantigens for the anti-neuronal cell antibodies would be a useful marker for CNS-Lupus.

Central nervous system involvement in systemic lupus erythematosus: cerebral imaging and serological profile in patients with and without overt neuropsychiatric manifestations

The aim of this study was to evaluate morphological and functional abnormalities by cerebral imaging in a series of systemic lupus erythematosus (SLE) patients with and without overt central nervous system (CNS) manifestations, and to detect possible relationships with clinical parameters and a large panel of autoantibodies, including those reactive against neurotypic and gliotypic antigens. 68 patients with SLE were investigated in a cross-sectional study which included clinical evaluation of symptoms, cerebral magnetic resonance imaging (MRI) and brain single photon emission tomography (SPECT) analysis, electroencephalography (EEG), and serological tests for antibodies directed against nuclear, cytoplasmic neuronal and glial cell-related antigens. The results of this study showed: (1) a significant positive association of (a) anti-glial fibrillary acidic protein (GFAP) serum antibodies with neuropsychiatric (NP) manifestations and (b) anti-serin proteinase 3 (anti-PR3/c-ANCA) serum antibodies with pathological cerebral SPECT; (2) the presence of significantly higher values of (a) SLICC organ damage index in patients with abnormal MRI and (b) SLAM activity index in patients with abnormal SPECT; and (3) the association of (a) abnormal MRI with nonactive NP manifestations and (b) combined abnormality of brain SPECT and MRI with the occurrence of overall overt NP manifestations and with those of the organic/major type. Neuropsychiatric manifestations, namely those of the organic/major type, appeared to be significantly associated to the presence of a serum antibody against GFAP, a gliotypic antigen. There was also evidence of an association between SPECT abnormality and the presence of anti-PR3 (c-ANCA). Furthermore, brain imaging by MRI and SPECT applied to SLE patients appears to express CNS involvement significantly related to specific categories of NP manifestations. The abnormalities detected by the two tests seem to be preferentially associated with different activity phases of the NP disorder or of the lupus disease.

Neurobehavioral alterations in autoimmune mice

Inbred MRL, NZB and BXSB strains of mice spontaneously develop a systemic, lupus-like autoimmune disease. The progress of autoimmunity is accompanied with a cascade of behavioral changes, most consistently observed in tasks reflective of emotional reactivity and the two-way avoidance learning task. Given the possibility that behavioral alterations may reflect a detrimental consequence of autoimmune-inflammatory processes and/or an adaptive response to chronic malaise, they are tentatively labeled as autoimmunity-associated behavioral syndrome (AABS). It is hypothesized that neuroactive immune factors (pro-inflammatory cytokines, brain-reactive antibodies) together with endocrine mediators (corticotropin-releasing factor, glucocorticoids) participate in the etiology of AABS. Since AABS develops natively, and has a considerable face and predictive validity, and since the principal pathway to autoimmunity is known, AABS may be a useful model for the study of CNS involvement in human autoimmune diseases and by extension, for testing autoimmune hypotheses of several mental disorders (major depression, schizophrenia, Alzheimer's disease, autism and AIDS-related dementia).

Systemic lupus erythematosus: immunopathogenesis of neurologic dysfunction

Neurologic complications of systemic lupus erythematosus (neuro-SLE) are common. The most frequent manifestations of neuro-SLE are seizures, encephalopathy, and behavioral changes, but a wide variety of other neurologic abnormalities affecting the central and peripheral nervous system and muscle also occur. Although the prevalence of neuro-SLE is high, the diversity of clinical presentations, the multiple potential etiologies, and the absence of sensitive and specific diagnostic tests render diagnosis difficult. Recent advances in understanding mechanisms of neuronal dysfunction combined with advances in imaging techniques, including functional imaging, should help in diagnosis and management. The mechanisms of neurologic injury can be divided into three broad categories. First, neuronal dysfunction may result from direct effects of the immune system on brain cells such as autoantibody binding to cell surface, immune complex deposition with secondary inflammation, and effects of cytokines. Second, immune- mediated injury to supportive structures such as the vasculature may also affect the nervous system by producing ischemia. Finally, the neuraxis may be affected by any one of several immune and non- immune effects of infection, toxins, and metabolic disturbances.

Controversies in lupus: nervous system involvement

What have we learned about CNS lupus in recent years? An enormous amount of knowledge on pathophysiology of antiphospholipid antibodies, in particular, has been gathered. Although hard evidence of a direct pathogenetic role of these antibodies in cerebral lupus is still lacking, it is generally felt that the multiple microinfarctions found in the brains of lupus patients are related to their presence. Better understanding of the pathogenesis of cerebral lupus will come from the study of experimental models, as it has been possible to develop an antiphospholipid antibody syndrome in mice. Because no specific laboratory test for CNS lupus is yet available, diagnosing the condition remains a challenge to every clinician. Techniques including neuropsychometric testing, quantitative EEG, and SPECT scans have taught us more about cognitive dysfunction and psychosis in patients with SLE. These categories remain the most difficult to define. The concept of hypercoagulability in SLE patients has diverted the direction of therapy from immunosuppression towards anticoagulation. It is of utmost importance that randomised trials are commenced in order to determine the optimal mode of anticoagulation for various groups of lupus patients. It will be necessary to conduct such trials under strict inclusion criteria, based on well defined patient categories. Such an enterprise will require international co-operation of investigators.

Affinity isolation of neuron-reactive antibodies in MRL/lpr mice

Autoantibodies from the MRL/lpr mice react with numerous proteins on neuronal cell surfaces. The purpose of this study was to isolate and characterize a population of autoantibodies reactive preferentially or exclusively with nervous system tissue. Using a purified plasma membrane preparation from brain cortex of balb/c mice coupled to diaminopropylamine agarose gel, we affinity-isolated antineuronal antibodies from pooled MRL/lpr immunoglobulins. The isolated immunoglobulins reacted with brain cortex plasma membranes and neuroblastoma cells (but not liver, kidney, or fibroblasts) by Western blot and indirect immunofluorescence with confocal microscopy. By Western blot, the epitopes in the brain cortex were proteins of apparent molecular weights 101, 63, 53, 43, 39, and 33, kd; the epitopes in the neuroblastoma cells were 63, 57, and 53 kd. Lectin column isolation revealed that the 101 and 63 kd epitopes were glycosylated. Indirect immunofluorescence revealed that the antibodies bound to the cell soma more intensely than to the cell processes of viable cultured neuroblastoma cells. The cell surface localization of this binding was confirmed by confocal microscopy. Within the central nervous system the antibodies bound more intensely to primary cultures of isolated neurons from fetal cortex than to hippocampal or neostriatal cells. With these antibodies we can begin studies of their potential pathogenic effects.

Brain reactive autoantibodies and cognitive impairment in systemic lupus erythematosus

Nervous system involvement in SLE encompasses a wide array of clinical manifestations which may reflect multiple etiologic factors including autoantibodies to nervous tissue antigens. The aim of the present study was to examine the association between autoantibodies to a wide range of brain antigens and cognitive abnormalities in an unselected population of 70 SLE patients. Using a battery of standardized neuropsychological tests, cognitive impairment was identified in 15/70 (21%) SLE patients compared with 1/25 (4%) patients with rheumatoid arthritis and 1/23 (4%) healthy subjects (P = 0.04). Integral membrane proteins were isolated from dissociated brain cells by temperature-induced phase separation with Triton X-114. Synaptosomes were isolated by differential centrifugation and membrane enriched fractions were prepared by lectin affinity chromatography. Western blotting identified IgG reactivity to a wide range of proteins (MW 22-52 K) in SLE patients. The proteins identified were distinct from well-characterized intracellular antigens including ribosomal P proteins. There was no significant difference in the prevalence of anti-brain antibodies between SLE patients who were cognitively impaired and those who were not impaired. Furthermore, there was no association between the presence of autoantibodies and subsets of cognitive dysfunction. These results suggest that circulating autoantibodies to brain antigens are not responsible for the abnormalities in cognitive function in SLE patients.

Lymphocyte and neuronal antigens in neuropsychiatric lupus: presence of an elutable, immunoprecipitable lymphocyte/neuronal 52 kd reactivity

OBJECTIVE

To examine specific lymphocyte or neuronal antigens immuno-precipitated by systemic lupus erythematosus (SLE) sera.

METHOD

SLE sera were screened for the presence of antibodies binding to surface antigens of CD4(+) HUT-78 or SK-N-SH and IMR-6 neuroblastoma cells using Western blotting or radioimmunoprecipitation.

RESULTS

IgG eluates from both lymphocytes and neuroblastoma cells recognised a 52 kd band in HUT 78 cell lysates. Eight sera studied further using radioimmunoprecipitation also demonstrated binding to a 52 kd antigen (4/8 on HUT-78, 8/8 on SK-N-SH cells), partially depleted by absorption with viable HUT-78.

CONCLUSION

A 52 kd antigen recognised by SLE sera on lymphocytes and neuronal cells may play a role in the pathogenesis of neuropsychiatric-SLE.

Lymphocyte antigens in neuropsychiatric systemic lupus erythematosus. Relationship of lymphocyte antibody specificities to clinical disease

OBJECTIVE

To examine the relationships among specific lymphocyte antigenic reactivities of lupus sera and central nervous system complications of systemic lupus erythematosus (SLE), lymphocytotoxic antibody (LCA) positivity, and specific cognitive impairment.

METHODS

Sera from 115 patients with SLE were examined for the presence of IgM- and IgG-class autoantibodies binding to surface target antigens on lymphocytes, by immunoblotting and microdroplet lymphocytotoxicity studies. Seventy-three of these patients also underwent detailed neuropsychological testing within the same time period.

RESULTS

Significant associations were found between reactivities to several lymphocyte antigenic moieties and neuropsychiatric SLE (NPSLE) or cognitive impairment. Specifically, immunoblot reactivities to 31-32-kd, 50-52-kd, 54-56-kd, and 97-98-kd targets were associated with clinical NPSLE; there was a significant association between reactivity to the 50-52-kd moiety in particular and cognitive impairment. There were also associations between LCA and immunoblot reactivity. Furthermore, the previously reported association between LCA positivity and specific visuospatial cognitive impairment was confirmed with data obtained from 2 different batteries of neuropsychological tests.

CONCLUSION

In some cases, specific antigenic targets of LCA-containing sera may be implicated in the pathogenesis of NPSLE:

Cerebrospinal fluid interleukin-6, prostaglandin E2 and autoantibodies in patients with neuropsychiatric systemic lupus erythematosus and central nervous system infections

Cerebrospinal fluid (CSF) from patients with a variety of central nervous system (CNS) disorders was assayed for cytokines, prostaglandins, and autoantibodies. CSF interleukin-6 (IL-6) in patients with CNS infection (374.24 +/- 92.61 pg/mL) and neuropsychiatric systemic lupus erythematosus (NP-SLE) (71.40 +/- 5.89 pg/mL) were significantly higher than in patients with CNS inflammation (33.92 +/- 29.36 pg/mL) or controls (non-inflammatory CNS diseases) (4.35 +/- 3.00 pg/mL). Interleukin-1 beta, interferon alpha, and tumor necrosis factor alpha were undetectable in these samples: CSF prostaglandin E2 (PGE2) also exhibited similar patterns as IL-6. CSF immunoglobulin G (IgG) in patients with NP-SLE (8.84 +/- 1.80 mg/dL) was much higher than in patients with CNS infection (4.65 +/- 3.09 mg/dL), CNS inflammation (2.54 +/- 1.24 mg/dL), or controls (2.11 +/- 1.03 mg/dL). CSF autoantibodies against calf thymus antigens were present in patients with NP-SLE but not in patients with CNS infection as demonstrated by immunoblot. These results suggest that high IL-6 and PGE2 in CSF favors the diagnosis of CNS infection, while modestly elevated IL-6, high IgG, and autoantibodies against calf thymus antigens in CSF are the features of NP-SLE.

Neuropsychiatric disease in Sjögren's syndrome: anti-ribosomal P and anti-neuronal antibodies

PURPOSE

Patients with Sjögren's syndrome (SS) may develop nonfocal (i.e., psychiatric and/or cognitive dysfunction) as well as focal, neuropsychiatric disease (CNS-SS). Anti-ribosomal P and anti-neuronal antibodies have been associated with nonfocal neuropsychiatric disease in systemic lupus erythematosus (SLE), particularly psychosis and depression. This study examines the spectrum of psychiatric and cognitive dysfunction observed in SS patients with focal, as well as nonfocal, central nervous system (CNS) disease and relates these observations to the presence of serum and cerebrospinal fluid (CSF) anti-ribosomal and anti-neuronal antibodies.

PATIENTS AND METHODS

One hundred thirty-one patients--patients with primary SS (n = 91), patients with secondary SS (n = 34), and mothers of infants with neonatal lupus erythematosus (NLE) (n = 6)--were studied. Patients were referred to a large tertiary referral center and the population was highly selected for CNS disease. Patients were evaluated clinically for focal and nonfocal CNS disease. Sera from 131 patients and 34 paired sera/CSF samples were examined by enzyme-linked immunosorbent assay and radioimmunoassay for the presence of anti-ribosomal P and anti-neuronal autoantibodies, respectively. Clinical features were categorized and autoantibody profiles obtained and correlated independently for statistical significance. Data were analyzed using the two-tailed Fisher exact test.

RESULTS

Psychiatric or cognitive impairment, usually mild or moderate, occurred in over 80% (63 of 77) of this highly selected population of SS patients, and more than 60% of patients (48 of 77) had both. Anti-ribosomal P antibodies occurred in six (4.6%) patients with SS and related disorders. None of the patients with primary SS had anti-ribosomal P antibodies, whereas they were present in a small number of patients with secondary SS (i.e., 4 of 34 [12%]) and in 2 of 6 mothers of infants with NLE. There was no correlation between nonfocal CNS disease, including psychosis or severe depression, and the presence of anti-ribosomal P antibodies. Paired serum CSF samples from 34 SS patients with active CNS disease, including 6 with psychosis and 5 with severe depression, did not contain either anti-ribosomal P or anti-neuronal antibodies. Anti-ribosomal P and anti-neuronal antibodies were present in a control subset of SLE patients defined serologically by the presence of anti-nDNA antibodies.

CONCLUSION

Patients with primary SS associated with CNS disease, including psychosis and depression, do not have serum or CSF autoantibodies to ribosomal P peptide or neuronal antigens, detected by binding to neuroblastoma cells. Thus, autoantibodies associated with nonfocal or diffuse CNS disease in classical SLE (particularly psychosis and depression) are not present in CNS-SS. The observations suggest that nonfocal CNS disease in CNS-SS and CNS-SLE may be mediated by different immunopathologic mechanisms. Potentially, these observations may have diagnostic and therapeutic implications in the management of patients with CNS-SS and patients with CNS-SLE.

Antibodies to brain integral membrane proteins in systemic lupus erythematosus

Wheat germ lectin affinity chromatography and temperature-induced phase separation with Triton X-114 were evaluated for the isolation of surface neuronal antigens from rat and human brain and from human neuroblastoma cell lines IMR-6 and SK-N-SH. Both techniques yielded surface proteins which were free of contamination by intracellular proteins but temperature-induced phase separation was technically less demanding and less expensive, required a shorter assay time and resulted in a superior quantity and quality of isolated proteins. Rat brain surface proteins were used for characterization of antineuronal antibody reactivity in sera from patients with systemic lupus erythematosus (SLE). Western blotting identified reactivity in 15 of 75 (20%) SLE sera compared to five of 95 (5%) normal controls (P 0.006). In rat brain the molecular weight of the individual proteins identified ranged from 59 kDa to 22 kDa. Six of these were also present in human brain and two were present in neuroblastoma cell lines. Absorption studies indicated that some of the antigenic proteins were either restricted to brain tissue or shared with other non-neuronal tissues. These techniques should facilitate the characterization of antineuronal antibody reactivities and lead to a clearer understanding of their role in the pathogenesis of autoimmune neurologic disease.

Brain synaptosomal antibodies in systemic lupus erythematosus

Nervous system involvement in systemic lupus erythematosus (SLE) has been linked to the production of autoantibodies that may bind to surface antigens on neuronal cells and cause cellular dysfunction. At present, little is known of the target antigens recognized by these antibodies. The aim of the present study was to examine reactivity to rat brain synaptosomes (RBS) in sera from patients with SLE. Sera from 73 unselected SLE patients and controls were studied. Crude RBS were prepared by differential centrifugation and enriched fractions of synaptosomes (SY-E), myelin (MY-E) and mitochondria (MI-E) were obtained by sucrose density centrifugation. Rat liver (RL) was used for control antigens. Wheat-germ lectin affinity chromatography yielded membrane-enriched fractions of RBS, RL and whole rat brain (WRB). Antibody binding was examined by Western blotting. IgM reactivity was detected in 12/73 sera (16%) and was directed to proteins of 62K, 48K 37K molecular weight. IgG reactivity was present in 5/73 sera (7%) to proteins of 52K, 48K, 37K and 29K molecular weight. Except for binding to the 52K and 37K proteins these autoantibodies were not detected in control sera. Reactivity was usually absent, or present in reduced amounts, in WRB and RL. Additional experiments revealed that binding of IgM to 62K was found predominantly in SY-E and MY-E fractions, 48K in SY-E and MI-E fractions and 37K in the SY-E fraction. Binding of IgG to 48K and 29K was detected in the SY-E and MI-E, but reactivity to 52K and 37K was restricted to the SY-E fraction. Thus, sera from SLE patients contain antibodies to synaptosomal antigens that may contribute to the neuropsychiatric manifestations of the disease.

Fluctuating cognitive abnormalities and cerebral glucose metabolism in neuropsychiatric systemic lupus erythematosus

Brain imaging techniques such as MRI and PET have the potential for identifying central nervous system involvement in SLE. They may also help elucidate the mechanisms giving rise to the widely diverging manifestations of CNS involvement in SLE. This report documents an intensive longitudinal study of three women with neuropsychiatric SLE. PET and neuropsychological evaluation were both used to examine the co-occurrence of behavioural/cognitive deficits with alterations in regional brain glucose metabolism. In all three patients, FDG uptake indicated abnormalities which were not identified on CT scan, but corresponded well with localisable cognitive deficits. Changes in each patient's cognitive profile on reassessment paralleled changes on PET. These findings support the suggestion that cognitive deficits in SLE patients reflect primary CNS involvement.

Systemic lupus erythematosus patients with central nervous system involvement show autoantibodies to a 50-kD neuronal membrane protein

An antibody was detected in the sera from patients with systemic lupus erythematosus (SLE) and central nervous system (CNS) involvement that reacted with a 50-kD antigen in the plasma membrane of brain synaptic terminals. The 50-kD antigen was solubilized with Triton X-100 from preparations enriched with synaptic plasma membranes, and was partially purified by molecular sieve filtration column chromatography. The sera of 19 of 20 CNS-SLE patients showed strong to moderate immunoreactivity with the 50-kD protein in Western blots. Immunoreactivity with the 50-kD protein was also detected in the cerebrospinal fluid of CNS-SLE patients. Control sera from healthy individuals did not react with the 50-kD protein. Low to background reactivity was detected in 35% of a group of SLE patients without CNS manifestations, and in 3% of patients displaying other connective tissue diseases. A total of 100 individuals were tested in this study. Purified autoantibodies to the 50-kD protein from CNS-SLE patients were used for immunofluorescent labeling of neuroblastoma cells. The immunofluorescent staining revealed a distinct macular distribution pattern on the surface of the cell membrane. Taken together, the data suggest that the 50-kD protein may be an important target for autoantibodies, preponderantly found in CNS-SLE patients, and that the antigen may play a role in the pathogenesis of some neurological manifestations in SLE.

Evidence for bound antineuronal antibodies in brains of NZB/W mice

Antibodies reactive with neuronal tissue are present in the sera of the murine models of systemic lupus erythematosus (SLE). Access of these antibodies to the central nervous system is an important prerequisite to the hypothesis that these antibodies affect neuronal function. In this study, we isolated antibodies from neutral and acid washes of brain parenchyma of NZB/W F1 mice. Antibody could be eluted from the brains of NZB/W F1 but not control mice. The immunoglobulin was predominantly IgG1; the binding characteristics of the brain eluted antibody were narrower than those of antibody from sera and eluted from visceral organ.

Diagnosis and pathogenesis of CNS lupus

The central nervous system (CNS) is clinically involved in approximately 40% of all systemic lupus erythematosis (SLE) patients. Minor psychiatric symptoms and abnormalities on neuropsychological testing are being detected with increasing frequency. This review summarizes current thinking concerning the diagnosis and pathogenesis of CNS lupus. The main symptoms of CNS lupus can be diffuse (generalized seizures, psychosis) or focal (stroke, peripheral neuropathies). Neuropsychiatric symptoms often occur in the first year of SLE, but are rarely the presenting symptoms of the disease. In studies on the pathology of CNS lupus, vasculopathy, infarcts and haemorrhages are often observed, whereas vasculitis is rare. Endocardial lesions and mural thrombi have also been reported in 33-50% of CNS lupus patients. In diagnostic imaging of the CNS, magnetic resonance imaging (MRI) scans often provide evidence for edema or small infarcts, both in focal and diffuse CNS lupus, whereas computerized tomography (CT) scans only show gross abnormalities. The first reports on position emission tomography (PET) scans in CNS lupus patients show decreased glucose uptake in the brain. The cerebral blood flow decreases during active diffuse and focal CNS lupus. The blood-brain barrier is somewhat more frequently impaired in diffuse CNS lupus. Intrathecal IgG and IgM production is observed in 25-66% of all CNS lupus patient. Various specificities of autoantibodies have been observed in CNS lupus. Of these, anticardiolipin (ACA) antibodies show a well-documented association with focal involvement of the CNS in SLE. These antibodies could cause thrombosis by interfering with the protein C pathway of fibrinolysis. In addition, they are associated with endocardial and valvular heart disease, which is often observed in SLE and which could cause embolism. The relation between ACA and diffuse CNS lupus is not yet clear. Low-avidity anti-DNA antibodies are also found in CNS lupus, possibly because of their cross-reaction with cardiolipin. Antineuronal antibodies and lymphocytotoxic antibodies have been associated with diffuse CNS lupus and abnormalities on neuropsychological testing. However, the population of these antibodies is rather heterogeneous and it has not been possible to assess a common target antigen. Therefore, it is still obscure whether there is also a second immune-mediated mechanism responsible for the development of the diffuse form of CNS lupus.

The association between sequential changes in serum antineuronal antibodies and neuropsychiatric systemic lupus erythematosus

To determine the significance of changes in serum antineuronal antibody levels in systemic lupus erythematosus, 9 patients who had a rise and 11 patients who had a fall in neuronal antibody titre over a mean duration of 2.1 years (range 0.25-5.2) were identified. These changes were examined in the light of concurrent changes in other serological variables, overall disease activity, neuropsychiatric disease and neuropsychological tests. Changes in antineuronal antibodies were frequently associated with concurrent changes in anti-DNA antibodies and overall disease activity. When neuropsychiatric disease or cognitive dysfunction were present, their course showed a close correlation with changes in antineuronal antibody levels. The results support the association between antineuronal antibodies and neuropsychiatric-systemic lupus erythematosus, but suggest that their measurement will provide useful information of disease status in only a subpopulation of patients.