The role of autoimmunity and brain inflammation in disorders of learning, behavior and autism

There is a large and growing body of evidence for the role of brain inflammation due to immune dysregulation in disorders of learning, behavior and autism. A study recently published in the journal Biological Psychiatry shows how the microglia (immune cells in the brain) are activated and increased in the prefrontal cortex in autism:

"In the neurodevelopmental disorder autism, several neuroimmune abnormalities have been reported. However, it is unknown whether microglial somal volume or density are altered in the cortex and whether any alteration is associated with age or other potential covariates."

The authors used advanced immunochemistry and nuclear imaging techniques to compare microglial activation and volume in autistic and normal brains. Their conclusion:

"Given its early presence, microglial activation may play a central role in the pathogenesis of autism in a substantial proportion of patients."

Autoimmune activity may manifest through a variety of autoantibodies to neural tissues in autistic spectrum disorders, epilepsy, Landau-Kleffner Syndrome (infantile acquired aphasia), etc. An earlier paper in Biological Psychiatry documents abnormal immune markers in the serum in association with these disorders:

"Brain derived neurotrophic factor (BDNF) elevation in newborn sera predicts intellectual/social developmental abnormalities. Other autoantibodies (AAs) to endothelial cells (ECs) and myelin basic protein (MBP) are also elevated in some children. We tested relationships between BDNF, BDNF AAs, and other AAs in children with these disorders."

The authors measured these immune 'attack molecules' in measured in children with autism, childhood disintegrative disorder (CDD), pervasive developmental delay-not otherwise specified (PDD-nos), acquired epilepsy, Landau-Kleffner syndrome (LKS); healthy children (HC), and children with non-neurological illnesses (NNI). The data showed significant elevations. Their conclusion:

"Children with developmental disorders and epilepsy have higher AAs to several neural antigens compared to controls. The presence of both BDNF AAs and elevated BDNF levels in some children with autism and CDD suggests a previously unrecognized interaction between the immune system and BDNF."

Immune dysregulation can manifest on a spectrum of developmental dysfunction from very mild development and learning disorders to full-blown autism. A recent paper in the same journal presents the evidence for immune dysfunction in healthy siblings of autistic kids:

"Endophenotypes are simple biological aspects of a disease that can be observed in unaffected relatives...an “autism endophenotype” justifies the observation that a mild reduction in ideational fluency and nonverbal generativity might be observed in healthy, unaffected relatives of children with autism...we examined whether the “autism endophenotype” would extend its effects on the immune system."

The authors tested multiple immune parameters in autistic kids and their siblings in comparison to healthy 'controls' without a family history for autism and came to this conclusion:

"Results of this pilot study indicate that a complex immune dysfunction is present both in autistic children and in their non-autistic siblings and show the presence of an “autism endophenotype” that expands its effects on immunologic functions."

An early paper published in Pediatric Neurology provides evidence of neuroinflammation in the cerebrospinal fluid in autism:

"In order to find evidence for neuroinflammation, we compared levels of sensitive indicators of immune activation: quinolinic acid, neopterin, and biopterin, as well as multiple cytokines and cytokine receptors, in cerebrospinal fluid and serum from children with autism, to control subjects with other neurologic disorders."

Neopterin and biopterin are easily measured in the urine. What did the data show?

"In cerebrospinal fluid from 12 children with autism, quinolinic acid and neopterin were decreased, and biopterin was elevated, compared with control subjects."

Subsequent research published in the same journal revealed the role of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) in cases of autism that became worse:

"Recent reports implicating elevated cytokines in the central nervous system in a small number of patients studied with autism have reported clinical regression."

The authors' measurements of TNF-α in the serum and CSF of autistic children resulted in data that painted this picture:

"Elevation of cerebrospinal fluid levels of tumor necrosis factor-alpha was significantly higher than concurrent serum levels in all of the patients studied. The ratio of the cerebrospinal fluid levels to serum levels averaged 53.7:1...This observation may offer a unique insight into central nervous system inflammatory mechanisms that may contribute to the onset of autism and may serve as a potential clinical marker."

Research just published in the journal Brain, Behavior, and Immunity reports the role of other pro-inflammatory cytokines in worsening cases of autistic spectrum disorder.

"A potential role for immune dysfunction has been suggested in Autism spectrum disorders (ASD). To test this hypothesis, we investigated evidence of differential cytokine release in plasma samples obtained from 2 to 5 year-old children with ASD compared with age-matched typically developing (TD) children and children with developmental disabilities other than autism."

The data painted an unmistakable and compelling picture:

"Observations indicate significant increases in plasma levels of a number of cytokines, including IL-1β, IL-6, IL-8 and IL-12p40 in the ASD group compared with TD controls. Moreover, when the ASD group was separated based on the onset of symptoms, it was noted that the increased cytokine levels were predominantly in ASD children who had a regressive form of ASD. In addition, increasing cytokine levels were associated with more impaired communication and aberrant behaviors."

Their conclusion is important for every clinician and parent to bear in mind:

"In conclusion, using larger number of participants than previous studies, we report significantly shifted cytokine profiles in ASD. These findings suggest that ongoing inflammatory responses may be linked to disturbances in behavior and require confirmation in larger replication studies. The characterization of immunological parameters in ASD has important implications for diagnosis, and should be considered when designing therapeutic strategies to treat core symptoms and behavioral impairments of ASD."

We can also be informed by a fascinating study published in Biological Psychiatry confirming that behavioral abnormalities are associated with autoimmune attack on hormones in the brain and periphery. The authors set out to resolve the biological mechanism involved in aggressive behavior:

"Altered stress response is characteristic for subjects with abnormal aggressive and antisocial behavior...We hypothesized that autoantibodies (autoAbs) directed against several stress-related neurohormones may exist in aggressive subjects."

Assays for antibodies revealed a definite pattern for both conduct disorder and prisoners groups leading the authors to conclude:

"High levels of ACTH-reactive autoAbs as well as altered levels of oxytocin- and vasopressin-reactive autoAbs found in aggressive subjects may interfere with the neuroendocrine mechanisms of stress and motivated behavior. Our data suggest a new biological mechanism of human aggressive behavior that involves autoAbs directed against several stress-related neurohormones."

We can also appreciate the evidence presented the Journal of Neuroimmunology that autism is characterized by a deficit in the ability to dampen autoimmune attack on the brain by the cytokine transforming growth factor beta-1 (TGFβ1):

"Autism spectrum disorders (ASD) are characterized by impairment in social interactions, communication deficits, and restricted repetitive interests and behaviors. There is evidence of both immune dysregulation and autoimmune phenomena in autism. We examined the regulatory cytokine transforming growth factor beta-1 (TGFβ1) because of its role in controlling immune responses."

The authors compared plasma levels of active TGFβ1 were in 75 children with ASD to 68 controls, finding that they were significantly lower in the ASD group. Moreover...

"...there were significant correlations between psychological measures and TGFβ1 levels, such that lower TGFβ1 levels were associated with lower adaptive behaviors and worse behavioral symptoms. The data suggest that immune responses in autism may be inappropriately regulated due to reductions in TGFβ1."

Their findings likely apply to a range of developmental, learning and behavioral disorders:

"Such immune dysregulation may predispose to the development of possible autoimmune responses and/or adverse neuroimmune interactions during critical windows in development."

Along these lines, a paper published in Biological Psychiatry describes the impaired immune tolerance due to deficiencies in regulatory T cells, another critical immune regulating factor in children with Tourette Syndrome. The authors state:

"Since regulatory T (T reg) cells play a major role in preventing autoimmunity, we hypothesized that a defect in T reg cells may be present in children with Tourette syndrome (TS)."

They analyzed the peripheral blood of TS kids compared to matched control subjects on multiple occasions to determine the numbers of CD4+CD25+CD69− T reg cells. The results were clear:

"A significant decrease in T reg cells was observed in patients with moderate to severe TS symptoms compared with healthy age-matched control children. A decrease in T reg cell number was also noted during symptom exacerbations in five out of six patients."

Their conclusion affirms the role of autoimmunity in Tourette syndrome:

"These data support our hypothesis that at least some TS patients may have a decreased capacity to inhibit autoreactive lymphocytes through a deficit in T reg cells. Interactions of host T cell immunity and microbial factors may also contribute to the pathogenesis of TS."

Early evidence for the role of autoimmunity in autism was presented in the journal Neuroscience Letters. The authors state:

"It is well established that increased neopterin levels are associated with activation of the cellular immune system and that reduced biopterins are essential for neurotransmitter synthesis. It has been suggested that some autistic children may be suffering from an autoimmune disorder."

They measured these pterins in the urine of pre-school autistic children, their siblings and age-matched control children and found:

"Both urinary neopterin and biopterin were raised in the autistic children compared to controls and the siblings showed intermediate values. This supports the possible involvement of cell-mediated immunity in the aetiology of autism."

The finding for the non-autistic siblings shows again that brain autoimmunity can manifest on a wide spectrum.Yet more evidence for autoimmune dysfunction in both kids with autism and their siblings was offered in a study published in the Journal of Neuroimmunology on antibrain antibodies:

"Serum autoantibodies to human brain, identified by ELISA and Western immunoblotting, were evaluated in 29 children with autism spectrum disorder (22 with autistic disorder), 9 non-autistic siblings and 13 controls."

The authors sum up the abnormalities found by concluding:

"Results suggest that children with autistic disorder and their siblings exhibit differences compared to controls in autoimmune reactivity to specific epitopes located in distinct brain regions."

No discussion of autoimmunity and the brain would be complete without considering the role of the gut, the site of 60-80% of all the immune system tissue in the body. A paper published in the Journal of Clinical Immunology describes the corresponding autoimmune intestinal inflammation in children with autism.

"A lymphocytic enterocolitis has been reported in a cohort of children with autistic spectrum disorder (ASD) and gastrointestinal (GI) symptoms. This study tested the hypothesis that dysregulated intestinal mucosal immunity with enhanced pro-inflammatory cytokine production is present in these ASD children."

The authors performed duodenal biopsies and measured CD3+ lymphocytes in the colonic mucosa for the presence of the pro-inflammatory cytokines TNF-α, IL-2, IL-4, IFN-γ and the anti-inflammatory IL-10. Again we see a clear expression of autoimmunity:

"Duodenal and colonic mucosal CD3+ lymphocyte counts were elevated in ASD children compared with noninflamed controls. In the duodenum...epithelial TNF-α+ cells in ASD children [were] significantly greater compared with noninflamed controls but not coeliac disease controls...IL-10+ cells were fewer in ASD children than in noninflamed controls. In the colon,TNF-α+ and CD3+IFN-γ+ were more frequent in ASD children than in noninflamed controls."

Note the similar findings for ASD and celiac disease. In striking accordance with with the authors found:

"There was a significantly greater proportion of TNF-α+ cells in colonic mucosa in those ASD children who had no dietary exclusion compared with those on a gluten and/or casein free diet. There is a consistent profile of lymphocyte cytokines in the small and large intestinal mucosa of these ASD children, involving increased pro-inflammatory and decreased regulatory activities."

It would be a shame for any clinician or parent to be unaware of their conclusion:

"The data provide further evidence of a diffuse mucosal immunopathology in some ASD children and the potential for benefit of dietary and immunomodulatory therapies."

Regarding the link between autoimmune inflammation in the gut and brain it's important to remember that the classical IgE-mediated food allergy diagnosed by skin prick is not usually the concern. Two papers published the Annals of Allergy, Asthma & Immunology illustrate the point. In IgE and non-IgE food allergy the authors note that:

"Food allergy (FA) is characterized by an abnormal immunologic reactivity to food proteins. The gastro-intestinal tract serves not only a nutritive function but also is a major immunologic organ. Although previously thought to be triggered primarily by an IgE-mediated mechanism of injury, considerable evidence now suggests that non-IgE mechanisms may also be involved in the pathogenesis of FA."

The authors gathered extensive data on a range of disorders including attention-deficit-hyperactivity disorder and behavioral disorders, and correlated them with immunologic deviations to Th1 or Th2 mechanisms of FA. Their conclusion is crucial knowledge for anyone treating food allergy mediated disorders:

"The results of this review allow the construction of a central, unifying hypothesis for a new classification of FA as follows: the clinical manifestations of FA, expressed in affected target organs, may be the result of immunologic injury mediated by interaction of food antigens with contiguous elements of mucosal associated lymphoid tissue. These appear to be modulated by relative imbalances of the Th1/Th2 paradigm, which may be the ultimate determinant governing the expression of FA as IgE-mediated, non-IgE-mediated, or mixed forms of IgE/non-IgE mechanisms of FA."

This is critically important because Th1 and Th2 imbalances require different interventions; it also offers a partial explanation of why antibody tests for food allergy are not reliable. The recent post on why autoimmune and allergic diseases are on the rise is of interest in this context. We also see in the same issue of Annals of Allergy, Asthma & Immunology a paper on the link between non-IgE-mediated food allergies and the inflamed lymphoid intestinal tissue that was described above in the report on mucosal immune activation and autism. Here the authors conclude:

"These studies suggest that abnormalities in Th1 function may not only play a role in some patients with non—IgE-mediated FA in whom decreased Th1 function is seen, but also in patients with celiac disease in whom an increased Th1 function is seen. The studies also suggest that lymphonodular hyperplasia may be a hallmark histologic lesion in patients with non—IgE-mediated FA."

What does lymphonodular hyperplasia feel like? Sometimes nothing more than a little bloating. All of this helps us to appreciate the significance of neurologic disorders with gluten sensitivity. This was explored in a paper published in the journal Pediatrics more than six years ago:

"During the past 2 decades, celiac disease (CD) has been recognized as a multisystem autoimmune disorder. A growing body of distinct neurologic conditions such as cerebellar ataxia, epilepsy, myoclonic ataxia, chronic neuropathies, and dementia have been reported, mainly in middle-aged adults. There still are insufficient data on the association of CD with various neurologic disorders in children, adolescents, and young adults, including more common and "soft" neurologic conditions, such as headache, learning disorders, attention-deficit/hyperactivity disorder (ADHD), and tic disorders. The aim of the present study is to look for a broader spectrum of neurologic disorders in CD patients, most of them children or young adults."

The authors found that kids with CD were far more likely to develop neurologic disorders than the control subjects, including hypotonia, developmental delay, learning disorders and ADHD, headache, and cerebellar ataxia. Thus their conclusion:

"This study suggests that the variability of neurologic disorders that occur in CD is broader than previously reported and includes "softer" and more common neurologic disorders, such as chronic headache, developmental delay, hypotonia, and learning disorders or ADHD."

Research published in the journal Nutritional Neuroscience clarifies one of the mechanisms behind autoimmune reaction to nervous system antigens in autism:

"We assessed the reactivity of sera from 50 autism patients and 50 healthy controls to specific peptides from gliadin and the cerebellum. A significant percentage of autism patients showed elevations in antibodies against gliadin and cerebellar peptides simultaneously."

The authors employed detailed antigen-antibody probes with confirmation by sophisticated DOT-immunoblot and inhibition studies to reach their conclusion:

"We conclude that a subgroup of patients with autism produce antibodies against Purkinje cells [a type of brain cell] and gliadin peptides, which may be responsible for some of the neurological symptoms in autism. "

Gliadin is the immunoreactive antigen contained in gluten.Mention should also be made of the ability of infections to sometimes trigger an autoimmune disorder as discussed in a study published in the Journal of Child Psychology and Psychiatry on PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcus infections).

"...(PANDAS) is a recently recognized syndrome in which pre-adolescent children have abrupt onsets of tics and/or obsessive-compulsive symptoms, a recurring and remitting course of illness temporally related to streptococcal infections, and associated neurologic findings including adventitious movements, hyperactivity and emotional lability.

The authors undertook a search for clinical and laboratory evidence and found consistent clinical findings have been described in a large case series, including magnetic resonance imaging that shows inflammatory changes in the basal ganglia, along with anti-basal ganglia antibodies have been found in some acute cases that were similar to those against streptococcal antigens. They note in their conclusion:

"PANDAS...has stimulated new research endeavors into the possible links between bacterial pathogens, autoimmune reactions, and neuropsychiatric symptoms."