Further characterization of autoantibodies to GABAergic neurons in the central nervous system produced by a subset of children with autism.

BACKGROUND: Autism is a neurodevelopmental disorder characterized by impairments in social interaction and deficits in verbal and nonverbal communication, together with the presence of repetitive behaviors or a limited repertoire of activities and interests. The causes of autism are currently unclear. In a previous study, we determined that 21% of children with autism have plasma autoantibodies that are immunoreactive with a population of neurons in the cerebellum that appear to be Golgi cells, which are GABAergic interneurons. METHODS: We have extended this analysis by examining plasma immunoreactivity in the remainder of the brain. To determine cell specificity, double-labeling studies that included one of the calcium-binding proteins that are commonly colocalized in GABAergic neurons (calbindin, parvalbumin or calretinin) were also carried out to determine which GABAergic neurons are immunoreactive. Coronal sections through the rostrocaudal extent of the macaque monkey brain were reacted with plasma from each of seven individuals with autism who had previously demonstrated positive Golgi cell staining, as well as six negative controls. In addition, brain sections from adult male mice were similarly examined. RESULTS: In each case, specific staining was observed for neurons that had the morphological appearance of interneurons. By double-labeling sections with plasma and with antibodies directed against γ-aminobutyric acid (GABA), we determined that all autoantibody-positive neurons were GABAergic. However, not all GABAergic neurons were autoantibody-positive. Calbindin was colabeled in several of the autoantibody-labeled cells, while parvalbumin colabeling was less frequently observed. Autoantibody-positive cells rarely expressed calretinin. Sections from the mouse brain processed similarly to the primate sections also demonstrated immunoreactivity to interneurons distributed throughout the neocortex and many subcortical regions. Some cell populations stained in the primate (such as the Golgi neurons in the cerebellum) were not as robustly immunoreactive in the mouse brain. CONCLUSIONS: These results suggest that the earlier report of autoantibody immunoreactivity to specific cells in the cerebellum extend to other regions of the brain. Further, these findings confirm the autoantibody-targeted cells to be a subpopulation of GABAergic interneurons. The potential impact of these autoantibodies on GABAergic disruption with respect to the etiology of autism is discussed herein.

Detection of autoantibodies to neural cells of the cerebellum in the plasma of subjects with autism spectrum disorders.

Autism spectrum disorders (ASD) are a group of heterogeneous, behaviorally defined disorders characterized by disturbances in social interaction and communication, often with repetitive and stereotyped behavior. Previous studies have described the presence of antibodies to various neural proteins in autistic individuals as well as post-mortem evidence of neuropathology in the cerebellum. We examined plasma from children with ASD, as well as age-matched typically developing controls, for antibodies directed against human cerebellar protein extracts using Western blot analysis. In addition, the presence of cerebellar specific antibodies was assessed by immunohistochemical staining of sections from Macaca fascicularis monkey cerebellum. Western blot analysis revealed that 13/63 (21%) of subjects with ASD possessed antibodies that demonstrated specific reactivity to a cerebellar protein with an apparent molecular weight of approximately 52 kDa compared with only 1/63 (2%) of the typically developing controls (p=0.0010). Intense immunoreactivity, to what was determined morphologically to be the Golgi cell of the cerebellum, was noted for 7/34 (21%) of subjects with ASD, compared with 0/23 of the typically developing controls. Furthermore, there was a strong association between the presence of antibodies reactive to the 52 kDa protein by Western blot with positive immunohistochemical staining of cerebellar Golgi cells in the ASD group (r=0.76; p=0.001) but not controls. These studies suggest that when compared with age-matched typically developing controls, children with ASD exhibit a differential antibody response to specific cells located in the cerebellum and this response may be associated with a protein of approximately 52 kDa.

Autoantibodies in autism spectrum disorders (ASD).

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disorders defined behaviorally by abnormalities in social, verbal, and nonverbal communication. The etiologies of ASD are unknown, likely to be the result of a variety of numerous genetic, neurological, environmental, and immunological interactions that lead to a general behavioral phenotype defined as ASD. This review will focus on the various immune system anomalies, in particular, autoantibodies, which have been reported in subjects with ASD. In addition, we will discuss recent studies performed by our group concerning the presence of autoantibodies directed against neural antigens, which are observed in patients with ASD.

Brain-specific autoantibodies in the plasma of subjects with autistic spectrum disorder.

Although autism spectrum disorder (ASD) is diagnosed on the basis of behavioral parameters, several studies have reported immune system abnormalities and suggest the possible role of autoimmunity in the pathogenesis of ASD. In this study we sought to assess the incidence of brain-specific autoantibodies in the plasma of children with autism (AU) compared to age-matched controls including, siblings without ASD, typically developing (TD) controls, and children with other developmental disabilities, but not autism (DD). Plasma from 172 individuals (AU, n = 63, median age: 43 months; TD controls, n = 63, median age: 48 months; siblings, n = 25, median age: 61 months; and DD controls, n = 21, median age: 38 months) was analyzed by Western blot for the presence of IgG antibodies against protein extracts from specific regions of the human adult brain including the hypothalamus and thalamus. The presence of a approximately 52 kDa MW band, in the plasma of subjects with AU, was detected with a significantly higher incidence when compared to plasma from TD controls (29% vs. 8%, P = 0.0027 and 30% vs. 11%, P = 0.01, in the thalamus and hypothalamus, respectively). Reactivity to three brain proteins (42-48 kDa MW), in particular in the hypothalamus, were observed with increased incidence in 37% of subjects with AU compared to 13% TD controls (P = 0.004). Multiple brain-specific autoantibodies are present at significantly higher frequency in children with AU. While the potential role of these autoantibodies in AU is currently unknown, their presence suggests a loss of self-tolerance to one or more neural antigens during early childhood.

The immune response in autism: a new frontier for autism research.

Autism spectrum disorders (ASD) are part of a broad spectrum of neurodevelopmental disorders known as pervasive developmental disorders, which occur in childhood. They are characterized by impairments in social interaction, verbal and nonverbal communication and the presence of restricted and repetitive stereotyped behaviors. At the present time, the etiology of ASD is largely unknown, but genetic, environmental, immunological, and neurological factors are thought to play a role in the development of ASD. Recently, increasing research has focused on the connections between the immune system and the nervous system, including its possible role in the development of ASD. These neuroimmune interactions begin early during embryogenesis and persist throughout an individual's lifetime, with successful neurodevelopment contingent upon a normal balanced immune response. Immune aberrations consistent with a dysregulated immune response, which so far, have been reported in autistic children, include abnormal or skewed T helper cell type 1 (T(H)1)/T(H)2 cytokine profiles, decreased lymphocyte numbers, decreased T cell mitogen response, and the imbalance of serum immunoglobulin levels. In addition, autism has been linked with autoimmunity and an association with immune-based genes including human leukocyte antigen (HLA)-DRB1 and complement C4 alleles described. There is potential that such aberrant immune activity during vulnerable and critical periods of neurodevelopment could participate in the generation of neurological dysfunction characteristic of ASD. This review will examine the status of the research linking the immune response with ASD.