Brain reactive monoclonal auto-antibodies: production and characterization

Circulating brain-reactive autoantibodies and behavioral deficits in the MRL model of CNS lupus

Brain-reactive autoantibodies (BRAA) are hypothesized to play a role in the neuropsychiatric manifestations that accompany systemic lupus erythematosus (SLE). The present study tests the proposed relation between circulating BRAA and behavioral deficits in lupus-prone MRL/lpr mice. Two age-matched cohorts born at different times were used to test the relationship in the context of altered disease severity. Significant correlations between autoimmunity and behavior were detected in both cohorts. These results are the first to report correlations between behavior and autoantibodies to integral membrane proteins of brain, supporting the hypothesis that BRAA contribute to the behavioral dysfunction seen in lupus.

Distribution and prevalence of leukocyte phenotypes in brains of lupus-prone mice

Autoantibody-mediated compromise of central neurotransmission is a pathogenic mechanism proposed in etiology of neuropsychiatric lupus (NP-SLE). Recent experimental data support the hypothesis that intrathecally-synthesized antibodies play a key role in brain damage and behavioral dysfunction. However, autoantibody-producing plasma cells have not yet been detected in brain tissue. We presently use contemporary immunohistochemical markers and flow cytometry to assess distribution and prevalence of plasma cells and other phenotypes, which infiltrate brains of lupus-prone MRL-lpr mice. The functional status of infiltrates was confirmed by in situ hybridization for TNF-alpha mRNA. Consistent with the notion of breached blood-CSF and blood-brain barriers, CD3+ T-cells (approximately 20% of the mononuclear cell infiltrate) were plentiful in choroid plexuses and commonly seen around blood vessels. The CD138+ plasma cells were restricted to the choroid plexus and stria medullaris of diseased MRL-lpr mice. Although accounting for less than 1% of the total cell infiltrate, CD19+IgM+ B-cells increased with age in brains of MRL-lpr mice. Severe mononuclear cell infiltration was accompanied by splenomegaly and retarded brain growth. The results obtained support the hypothesis of progressive neurodegeneration as a consequence of leukocyte infiltration and intrathecal autoantibody synthesis. Further characterization of neuroactive antibodies and their targets may contribute to a better understanding of brain atrophy and behavioral dysfunction in the MRL model, and potentially in NP-SLE.

Novel brain reactive autoantibodies: Prevalence in systemic lupus erythematosus and association with psychoses and seizures

Autoantibodies can cause neuropsychiatric manifestations in lupus patients by altering the physiological function of neuronal cells. In this study, we identified Brain Reactive Autoantibodies (BRAAs) against murine neuronal membrane proteins (M.W. 27.5 and 29.5 kD) and found them correlating with psychosis and/or seizures in lupus patients. They were specific to neuronal membrane tissues of mammalian origin and are significantly associated with psychosis and/or seizures (p<0.0001). These membrane proteins mass spectrometry profiles did not match to any published protein sequences. These BRAAs may play important roles in the pathophysiology of neuropsychiatric lupus.

Behavioral heterogeneity in an animal model of neuropsychiatric lupus

BACKGROUND

Various psychiatric manifestations of unknown etiology are common in systemic autoimmune disease lupus erythematosus (SLE). Profound heterogeneity at clinical and neuropathological levels suggests distinct subpopulations of SLE patients and multiple mechanisms in the pathogenesis of aberrant behavior. Using inbred mice prone to SLE-like condition, we presently examine whether subpopulations of diseased mice can be identified on the basis of their behavioral performance.

METHODS

Hierarchical cluster analysis was used to classify 105 MRL-lpr males into clusters. Multivariate analysis of variance (MANOVA) and discriminant function analysis were used to detect overall differences and identify discriminative variables.

RESULTS

Cluster 1 was characterized by blunted responsiveness to palatable stimulation, as well as increased spleen mass and serum levels of interleukin-1. Cluster 2 comprised of animals with reduced ambulation speed and enlarged spleen. Mice from cluster 3 showed profound dilatation of brain ventricles, reduced brain mass, impaired nutrition and performance in task reflective of emotional reactivity.

CONCLUSIONS

Present results suggest that systemic autoimmunity compromises brain function via non-Mendelian mechanisms. Although neuroactive cytokines may impair reward systems, brain atrophy seems to underlie deficits in ingestive behavior and emotional reactivity. This study supports the hypothesis that multiple neuroimmunological pathways are involved in the etiology of aberrant behavior during SLE-like disease.

Hippocampal damage in mouse and human forms of systemic autoimmune disease

Systemic lupus erythematosus (SLE) is frequently accompanied by neuropsychiatric (NP) and cognitive deficits of unknown etiology. By using autoimmune MRL-lpr mice as an animal model of NP-SLE, we examine the relationship between autoimmunity, hippocampal damage, and behavioral dysfunction. Fluoro Jade B (FJB) staining and anti-ubiquitin (anti-Ub) immunocytochemistry were used to assess neuronal damage in young (asymptomatic) and aged (diseased) mice, while spontaneous alternation behavior (SAB) was used to estimate the severity of hippocampal dysfunction. The causal relationship between autoimmunity and neuropathology was tested by prolonged administration of the immunosuppressive drug cyclophosphamide (CY). In comparison to congenic MRL +/+ controls, SAB acquisition rates and performance in the "reversal" trial were impaired in diseased MRL-lpr mice, suggesting limited use of the spatial learning strategy. FJB-positive neurons and anti-Ub particles were frequent in the CA3 region. Conversely, CY treatment attenuated the SAB deficit and overall FJB staining. Similarly to mouse brain, the hippocampus from a patient who died from NP-SLE showed reduced neuronal density in the CA3 region and dentate gyrus, as well as increased FJB positivity in these regions. Gliosis and neuronal loss were observed in the gray matter, and T lymphocytes and stromal calcifications were common in the choroid plexus. Taken together, these results suggest that systemic autoimmunity induces significant hippocampal damage, which may underlie affective and cognitive deficits in NP-SLE.

Altered neurotransmission in brains of autoimmune mice: pharmacological and neurochemical evidence

Depressive-like behavior is the most profound manifestation of autoimmunity-associated behavioral syndrome in lupus-prone MRL-lpr mice. This led to the hypothesis that chronic autoimmunity and inflammation alter the activity of central serotonergic and dopaminergic systems. Three drugs with a selective mode of action were used to probe the functional status of these two systems in vivo. The behavioral effects of single and repeated intraperitoneal (i.p.) injections of sertraline, quinpirole (QNP) and risperidone were measured in the forced swim and brief sucrose preference tests. In comparison to MRL +/+ controls, autoimmune MRL-lpr mice did not show a reduction in sucrose intake after the administration of sertraline. Acute injection of quinpirole increased floating more in the MRL-lpr than in the control group, while intermittent administration induced self-injurious behavior in both groups. Acute injection of risperidone significantly increased floating in MRL-lpr mice, while repeated administration abolished the difference between the substrains in sucrose intake. These discrepancies in responsiveness implied that the central neurotransmitter activity is dissimilar in the two MRL substrains. This notion was confirmed in a cohort of untreated MRL-lpr and MRL +/+ mice by comparing their neurotransmitter/metabolite levels in several brain regions. In particular, MRL-lpr brains showed increased dopamine (DA) levels in the paraventricular nucleus (PVN) and median eminence (ME), decreased concentrations of serotonin in the PVN and enhanced levels in the hippocampus, as well as decreased norepinephrine (NE) levels in the prefrontal cortex. Behavioral deficits correlated with the changes in PVN and median eminence. These results are consistent with the hypothesis that imbalanced neurotransmitter regulation of the hypothalamus-pituitary axis plays an important role in the etiology of behavioral dysfunction induced by systemic autoimmune disease.

Animal models for nervous system disease in systemic lupus erythematosus

Animal models have much to teach us about nervous system dysfunction in SLE. It should be stressed that the murine strains described in this review have variable expression in the onset and severity of clinical and serological features, perhaps making them more like a heterogeneous human population with SLE. With this in mind, studies involving animal models like those involving human subjects should use a sample size that ensures adequate power. It is not surprising that studies that use sample sizes as low as four to five animals per group would find discrepant results, especially in outcomes that are measured prior to the terminal phases of the disease. Similar to human SLE patients, murine models have systemic autoimmune as well as neurological manifestations. Studies with murine models must continue to consider some type of SLE disease activity measures in order to control for the effects of systemic disease on nervous system dysfunction. Because of the short time window between the earliest evidence of neurologic dysfunction and severe autoimmune disease manifestations, especially in MRL/lpr mice, the disease acceleration model may allow a more careful dissection of how immunological events are related to nervous system dysfunction. Alternatively, the study of MRL/lpr mice ultraearly (e.g., 3 weeks of age) could also provide invaluable information about the first events leading to nervous system dysfunction in SLE. Both approaches promise to identify predictors of specific nervous system manifestations that may suggest novel and more specific therapeutic interventions.

Circulating autoantibodies to a 240 kD fetal brain protein

Antibodies (IgG and IgM) recognizing a 240 kD antigen of the cat fetal brain were found in sera of healthy people and in sera (IgG) obtained at uncomplicated delivery from the umbilical cord of the newborn infant. The method applied was immunoblotting. Using the same method, the 240 kD antigen could not be detected in the adult brain or other fetal tissues. It seems that the antigen is specific for the fetal brain. The role of the antigen and the origin of generation and significance of function of the antibodies in the circulation are the objects of our further studies.