Circulating autoantibodies recognize and bind dying neurons following injury to the brain

Traumatic Brain Injury: A Comprehensive Review of Biomechanics and Molecular Pathophysiology

Traumatic brain injury (TBI) is a critical public health concern with profound consequences for affected individuals. This comprehensive literature review delves into TBI intricacies, encompassing primary injury biomechanics and the molecular pathophysiology of the secondary injury cascade. Primary TBI involves a complex interplay of forces, including impact loading, blast overpressure, and impulsive loading, leading to diverse injury patterns. These forces can be categorized into inertial (e.g., rotational acceleration causing focal and diffuse injuries) and contact forces (primarily causing focal injuries like skull fractures). Understanding their interactions is crucial for effective injury management. The secondary injury cascade in TBI comprises multifaceted molecular and cellular responses, including altered ion concentrations, dysfunctional neurotransmitter networks, oxidative stress, and cellular energy disturbances. These disruptions impair synaptic function, neurotransmission, and neuroplasticity, resulting in cognitive and behavioral deficits. Moreover, neuroinflammatory responses play a pivotal role in exacerbating damage. As we endeavor to bridge the knowledge gap between biomechanics and molecular pathophysiology, further research is imperative to unravel the nuanced interplay between mechanical forces and their consequences at the molecular and cellular levels, ultimately guiding the development of targeted therapeutic strategies to mitigate the debilitating effects of TBI. In this study, we aim to provide a concise review of the bridge between biomechanical processes causing primary injury and the ensuing molecular pathophysiology of secondary injury, while detailing the subsequent clinical course for this patient population. This knowledge is crucial for advancing our understanding of TBI and developing effective interventions to improve outcomes for those affected.

Immune Regulatory Functions of Macrophages and Microglia in Central Nervous System Diseases

Macrophages can be characterized as a very multifunctional cell type with a spectrum of phenotypes and functions being observed spatially and temporally in various disease states. Ample studies have now demonstrated a possible causal link between macrophage activation and the development of autoimmune disorders. How these cells may be contributing to the adaptive immune response and potentially perpetuating the progression of neurodegenerative diseases and neural injuries is not fully understood. Within this review, we hope to illustrate the role that macrophages and microglia play as initiators of adaptive immune response in various CNS diseases by offering evidence of: (1) the types of immune responses and the processes of antigen presentation in each disease, (2) receptors involved in macrophage/microglial phagocytosis of disease-related cell debris or molecules, and, finally, (3) the implications of macrophages/microglia on the pathogenesis of the diseases.

Increased plasma and brain immunoglobulin A in Alzheimer’s disease is lost in apolipoprotein E ε4 carriers

Background

Alzheimer’s disease (AD) is foremost characterized by β-amyloid (Aβ)-extracellular plaques, tau-intraneuronal fibrillary tangles (NFT), and neuroinflammation, but over the last years it has become evident that peripheral inflammation might also contribute to the disease. AD patients often demonstrate increased levels of circulating proinflammatory mediators and altered antibody levels in the blood. In our study, we investigated the plasma Immunoglobulin A (IgA) levels in association with apolipoprotein E (APOE) ε4 status and Aβ pathology.

Methods

IgA levels in antemortem-collected (cohort I) and postmortem-collected (cohort II) plasma samples from AD patients (n = 30 in cohort I and n = 16 in cohort II) and non-demented age-matched controls (NC) (n = 42 in cohort I and n = 7 in cohort II) were measured using ELISA. Hippocampal sections from cohort II were immunostained against IgA, and the IgA area fraction as well as the number of IgA positive (IgA+) cells in the cornu ammonis region were analysed using ImageJ. The relationship between plasma IgA levels and cognition, C-reactive protein (CRP), and cerebrospinal fluid (CSF) AD biomarkers in cohort I as well as neuropathology, IgA+ cell number, and IgA area fraction in cohort II was analysed before and after grouping the cohorts into APOEε4 carriers and APOEε4 non-carriers.

Results

Plasma IgA levels were higher in AD patients compared to NC in both cohorts. Also, AD patients demonstrated higher IgA area fraction and IgA+ cell number compared to NC. When APOEε4 status was considered, higher plasma IgA levels in AD patients were only seen in APOEε4 non-carriers. Finally, plasma IgA levels, exclusively in APOEε4 non-carriers, were associated with cognition, CRP, and CSF Aβ levels in cohort I as well as with IgA area fraction, IgA+ cell number, and Aβ, Lewy body, and NFT neuropathology in cohort II.

Conclusions

Our study suggests that AD pathology and cognitive decline are associated with increased plasma IgA levels in an APOE allele-dependent manner, where the associations are lost in APOEε4 carriers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01062-z.

Modeling the Dynamics of a Secondary Neurodegenerative Injury Following a Mild Traumatic Brain Injury

During a traumatic brain injury (TBI), there is an injection of glial fibrillary acidic protein (GFAP) from the brain into the bloodstream through a lesion in the blood-brain barrier (BBB). In the blood, a bio controller responds by up-regulating Immunoglobulin G (IgG) production into the bloodstream to remove the excess protein. Here, we model the concentrations over time of GFAP and IgG in the bloodstream following a mild TBI. We apply these dynamics to repeated traumas that aggravate the recovery process, as well as increasing the severity of injury. Both show substantially elevated and prolonged GFAP levels. This research and model is clinically relevant in that it could lead to the analyzation of GFAP levels in the brain through methods as simple as a blood draw. This information can be used to predict the extent of brain lesions as well as help understand the recovery process that the brain takes when having undergone a TBI.

Complex Autoantibody Responses Occur following Moderate to Severe Traumatic Brain Injury

Most of the variation in outcome following severe traumatic brain injury (TBI) remains unexplained by currently recognized prognostic factors. Neuroinflammation may account for some of this difference. We hypothesized that TBI generated variable autoantibody responses between individuals that would contribute to outcome. We developed a custom protein microarray to detect autoantibodies to both CNS and systemic Ags in serum from the acute-phase (the first 7 d), late (6-12 mo), and long-term (6-13 y) intervals after TBI in human patients. We identified two distinct patterns of immune response to TBI. The first was a broad response to the majority of Ags tested, predominantly IgM mediated in the acute phase, then IgG dominant at late and long-term time points. The second was responses to specific Ags, most frequently myelin-associated glycopeptide (MAG), which persisted for several months post-TBI but then subsequently resolved. Exploratory analyses suggested that patients with a greater acute IgM response experienced worse outcomes than predicted from current known risk factors, suggesting a direct or indirect role in worsening outcome. Furthermore, late persistence of anti-MAG IgM autoantibodies correlated with raised serum neurofilament light concentrations at these time points, suggesting an association with ongoing neurodegeneration over the first year postinjury. Our results show that autoantibody production occurs in some individuals following TBI, can persist for many years, and is associated with worse patient outcome. The complexity of responses means that conventional approaches based on measuring responses to single antigenic targets may be misleading.

Immunoglobulin A Autoreactivity toward Brain Enriched and Apoptosis-Regulating Proteins in Saliva of Athletes after Acute Concussion and Subconcussive Impacts

The diagnosis and management of concussion is hindered by its diverse clinical presentation and assessment tools reliant on subjectively experienced symptoms. The biomechanical threshold of concussion is also not well understood, and asymptomatic concussion or "subconcussive impacts" of variable magnitudes are common in contact sports. Concerns have risen because athletes returning to activity too soon have an increased risk of prolonged recovery or long-term adverse health consequences. To date, little is understood on a molecular level regarding concussion and subconcussive impacts. Recent research suggests that neuroinflammatory mechanisms may serve an important role subsequent to concussion and possibly to subconcussive impacts. These studies suggest that autoantibodies may be a valuable tool for detection of acute concussion and monitoring for changes caused by cumulative exposure to subconcussive impacts. Hence, we aimed to profile the immunoglobulin (Ig)A autoantibody repertoire in saliva by screening a unique sport-related head trauma biobank. Saliva samples (n = 167) were donated by male and female participants enrolled in either the concussion (24-48 h post-injury) or subconcussion (non-concussed participants having moderate or high cumulative subconcussive impact exposure) cohorts. Study design included discovery and verification phases. Discovery aimed to identify new candidate autoimmune targets of IgA. Verification tested whether concussion and subconcussion cohorts increased IgA reactivity and whether cohorts showed similarities. The results show a significant increase in the prevalence of IgA toward protein fragments representing 5-hydroxytryptamine receptor 1A (HTR1A), serine/arginine repetitive matrix 4 (SRRM4) and FAS (tumor necrosis factor receptor superfamily member 6) after concussion and subconcussion. These results may suggest that concussion and subconcussion induce similar physiological effects, especially in terms of immune response. Our study demonstrates that saliva is a potential biofluid for autoantibody detection in concussion and subconcussion. After rigorous confirmation in much larger independent study sets, a validated salivary autoantibody assay could provide a non-subjective quantitative means of assessing concussive and subconcussive events.

Anti-Pituitary and Anti-Hypothalamus Autoantibody Associations with Inflammation and Persistent Hypogonadotropic Hypogonadism in Men with Traumatic Brain Injury

Traumatic brain injury (TBI) and can lead to persistent hypogonadotropic hypogonadism (PHH) and poor outcomes. We hypothesized that autoimmune and inflammatory mechanisms contribute to PHH pathogenesis. Men with moderate-to-severe TBI (n = 143) were compared with healthy men (n = 39). The TBI group provided blood samples 1-12 months post-injury (n = 1225). TBI and healthy control (n = 39) samples were assayed for testosterone (T) and luteinizing hormone (LH) to adjudicate PHH status. TBI samples 1-6 months post-injury and control samples were assayed for immunoglobulin M (IgM)/immunoglobulin G (IgG) anti-pituitary autoantibodies (APA) and anti-hypothalamus autoantibodies (AHA). Tissue antigen specificity for APA and AHA was confirmed via immunohistochemistry (IHC). IgM and IgG autoantibodies for glial fibrillary acid protein (GFAP) (AGA) were evaluated to gauge APA and AHA production as a generalized autoimmune response to TBI and to evaluate the specificity of APA and AHA to PHH status. An inflammatory marker panel was used to assess relationships to autoantibody profiles and PHH status. Fifty-one men with TBI (36%) had PHH. An age-related decline in T levels by both TBI and PHH status were observed. Injured men had higher APA IgM, APA IgG, AHA IgM, AHA IgG, AGA IgM, and AGA IgG than controls (p < 0.0001 all comparisons). However, only APA IgM (p = 0.03) and AHA IgM (p = 0.03) levels were lower in the PHH than in the non-PHH group in multivariate analysis. There were no differences in IgG levels by PHH status. Multiple inflammatory markers were positively correlated with IgM autoantibody production. PHH was associated with higher soluble tumor-necrosis-factor receptors I/II, (sTNFRI, sTNFRII), regulated on activation, normal T-cell expressed and secreted (RANTES) and soluble interleukin-2-receptor-alpha (sIL-2Rα) levels. Higher IgM APA, and AHA, but not AGA, in the absence of PHH may suggest a beneficial or reparative role for neuroendocrine tissue-specific IgM autoantibody production against PHH development post-TBI.

The role of autoimmunity in pituitary dysfunction due to traumatic brain injury

PURPOSE

Traumatic brain injury (TBI) is one of the most common causes of mortality and long-term disability and it is associated with an increased prevalence of neuroendocrine dysfunctions. Post-traumatic hypopituitarism (PTHP) results in major physical, psychological and social consequences leading to impaired quality of life. PTHP can occur at any time after traumatic event, evolving through various ways and degrees of deficit, requiring appropriate screening for early detection and treatment. Although the PTHP pathophysiology remains to be elucitated, on the basis of proposed hypotheses it seems to be the result of combined pathological processes, with a possible role played by hypothalamic-pituitary autoimmunity (HPA). This review is aimed at focusing on this possible role in the development of PTHP and its potential clinical consequences, on the basis of the data so far appeared in the literature and of some results of personal studies on this issue.

METHODS

Scrutinizing the data so far appeared in literature on this topic, we have found only few studies evaluating the autoimmune pattern in affected patients, searching in particular for antipituitary and antihypothalamus autoantibodies (APA and AHA, respectively) by simple indirect immunofluorescence.

RESULTS

The presence of APA and/or AHA at high titers was associated with an increased risk of onset/persistence of PTHP.

CONCLUSIONS

HPA seems to contribute to TBI-induced pituitary damage and related PTHP. However, further prospective studies in a larger cohort of patients are needed to define etiopathogenic and diagnostic role of APA/AHA in development of post-traumatic hypothalamic/pituitary dysfunctions after a TBI.

Amyloid-Beta 1-42 Cross-Reactive Antibody Prevalent in Human Sera May Contribute to Intraneuronal Deposition of A-Beta-P-42

Antibodies against many neural antigens are detected in the sera of both patients with Alzheimer's disease (AD) and some healthy individuals. Blood-brain barrier dysfunction could make it possible for brain-reactive autoantibodies to reach the brain, where they can react with amyloid ß peptide (AßP). The origin of these autoreactive antibodies in the blood is unclear. The goals of this study were as follows: (1) to examine the immune reactivity of anti-AßP-42 with 22 neuronal and other associated antigens, some of which are involved in the pathophysiology of AD; (2) to classify antibodies to these 22 different antigens into those that cross-react with AßP-42 and those that do not; (3) to determine whether these antibodies react with BBB proteins, nerve growth factors, and enteric neuronal antigens. Using monoclonal AßP-42 antibody and ELISA methodology, we found that the antibody was highly reactive with Aß protein, tau protein, presenilin, rabaptin-5, β-NGF, BDNF, mTG, and enteric nerve. The same antibody produced equivocal to moderate reactions with glutamate-R, S100B, AQP4, GFAP, MBP, α-synuclein, tTG-2, and tTG-3, and not with the rest. These antibodies were also measured in blood samples from 47 AD patients and 47 controls. IgG antibodies were found to be elevated against AßP-42 and many other antigens in a significant percentage of controls. Overall, the mean OD values were significantly higher against 9/23 tested antigens (p <0.001) in the samples with AD. We were indeed able to classify the detected neuronal antibodies into those that cross-react with AßP-42 and those that do not. Our main finding is that although these antibodies may be harmless in a subgroup of controls, in individuals with compromised BBBs these antibodies that cross-react with AßP-42 can reach the brain, where their cross-reactivity with AßP-42 may contribute to the onset and progression of AD, and perhaps other neurodegenerative disorders.

[Results of multicenter study of efficacy and safety of divaza in the treatment of the asthenic and mild to moderate cognitive disorders in elderly and senile subjects]

AIM

To study the efficacy and safety of divasa in elderly and senile subjects with asthenic and mild to moderate cognitive disorders.

MATERIAL AND METHODS

The study included 126 patients with clinically significant asthenia and mild to moderate cognitive disorders. Asthenia was assessed with MFI-20, cognitive disorders with MMSE, clock drawing test and verbal association test. All patients were treated with divasa in dose 2 tablets 3 times a day.

RESULTS AND CONCLUSION

The efficacy and safety of divasa in asthenic and mild to moderate cognitive disorders in elderly and senile subjects were shown. There is a need for a multicenter placebo-controlled trial on the efficacy of divasa to treat cognitive and asthenic disorders in elderly patients.

Neurofilament light as an immune target for pathogenic antibodies

Antibodies to neuronal antigens are associated with many neurological diseases including paraneoplastic neurological disorders, epilepsy, amyotrophic lateral sclerosis and multiple sclerosis. Immunization with neuronal antigens such as neurofilament light (NF-L), a neuronal intermediate filament in axons, has been shown to induce neurological disease and spasticity in mice. Also, although antibodies to NF-L are widely used as surrogate biomarkers of axonal injury in amyotrophic lateral sclerosis and multiple sclerosis, it remains to be elucidated if antibodies to NF-L contribute to neurodegeneration and neurological disease. To address this, we examined the pathogenic role of antibodies directed to NF-L in vitro using spinal cord co-cultures and in vivo in experimental autoimmune encephalomyelitis (EAE) and optic neuritis animal models of multiple sclerosis. Here we show that peripheral injections of antibodies to NF-L augmented clinical signs of neurological disease in acute EAE, increased retinal ganglion cell loss in experimental optic neuritis and induced neurological signs following intracerebral injection into control mice. The pathogenicity of antibodies to NF-L was also observed in spinal cord co-cultures where axonal loss was induced. Taken together, our results reveal that as well as acting as reliable biomarkers of neuronal damage, antibodies to NF-L exacerbate neurological disease, suggesting that antibodies to NF-L generated during disease may also be pathogenic and play a role in the progression of neurodegeneration.

Neuropathology of SUDEP: Role of inflammation, blood-brain barrier impairment, and hypoxia

Objective:

To seek a neuropathologic signature of sudden unexpected death in epilepsy (SUDEP) in a postmortem cohort by use of immunohistochemistry for specific markers of inflammation, gliosis, acute neuronal injury due to hypoxia, and blood-brain barrier (BBB) disruption, enabling the generation of hypotheses about potential mechanisms of death in SUDEP.

Methods:

Using immunohistochemistry, we investigated the expression of 6 markers (CD163, human leukocyte antigen–antigen D related, glial fibrillary acid protein, hypoxia-inducible factor-1α [HIF-1α], immunoglobulin G, and albumin) in the hippocampus, amygdala, and medulla in 58 postmortem cases: 28 SUDEP (definite and probable), 12 epilepsy controls, and 18 nonepileptic sudden death controls. A semiquantitative measure of immunoreactivity was scored for all markers used, and quantitative image analysis was carried out for selected markers.

Results:

Immunoreactivity was observed for all markers used within all studied brain regions and groups. Immunoreactivity for inflammatory reaction, BBB leakage, and HIF-1α in SUDEP cases was not different from that seen in control groups.

Conclusions:

This study represents a starting point to explore by immunohistochemistry the mechanisms underlying SUDEP in human brain tissue. Our approach highlights the potential and importance of considering immunohistochemical analysis to help identify biomarkers of SUDEP. Our results suggest that with the markers used, there is no clear immunohistochemical signature of SUDEP in human brain.

Lesion Size Is Exacerbated in Hypoxic Rats Whereas Hypoxia-Inducible Factor-1 Alpha and Vascular Endothelial Growth Factor Increase in Injured Normoxic Rats: A Prospective Cohort Study of Secondary Hypoxia in Focal Traumatic Brain Injury

BACKGROUND

Hypoxia following traumatic brain injury (TBI) is a severe insult shown to exacerbate the pathophysiology, resulting in worse outcome. The aim of this study was to investigate the effects of a hypoxic insult in a focal TBI model by monitoring brain edema, lesion volume, serum biomarker levels, immune cell infiltration, as well as the expression of hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

Female Sprague-Dawley rats (n = 73, including sham and naive) were used. The rats were intubated and mechanically ventilated. A controlled cortical impact device created a 3-mm deep lesion in the right parietal hemisphere. Post-injury, rats inhaled either normoxic (22% O2) or hypoxic (11% O2) mixtures for 30 min. The rats were sacrificed at 1, 3, 7, 14, and 28 days post-injury. Serum was collected for S100B measurements using ELISA. Ex vivo magnetic resonance imaging (MRI) was performed to determine lesion size and edema volume. Immunofluorescence was employed to analyze neuronal death, changes in cerebral macrophage- and neutrophil infiltration, microglia proliferation, apoptosis, complement activation (C5b9), IgG extravasation, HIF-1α, and VEGF.

RESULTS

The hypoxic group had significantly increased blood levels of lactate and decreased pO2 (p < 0.0001). On MRI post-traumatic hypoxia resulted in larger lesion areas (p = 0.0173), and NeuN staining revealed greater neuronal loss (p = 0.0253). HIF-1α and VEGF expression was significantly increased in normoxic but not in hypoxic animals (p < 0.05). A trend was seen for serum levels of S100B to be higher in the hypoxic group at 1 day after trauma (p = 0.0868). No differences were observed between the groups in cytotoxic and vascular edema, IgG extravasation, neutrophils and macrophage aggregation, microglia proliferation, or C5b-9 expression.

CONCLUSION

Hypoxia following focal TBI exacerbated the lesion size and neuronal loss. Moreover, there was a tendency to higher levels of S100B in the hypoxic group early after injury, indicating a potential validity as a biomarker of injury severity. In the normoxic group, the expression of HIF-1α and VEGF was found elevated, possibly indicative of neuro-protective responses occurring in this less severely injured group. Further studies are warranted to better define the pathophysiology of post-TBI hypoxia.

Histamine Induces Alzheimer's Disease-Like Blood Brain Barrier Breach and Local Cellular Responses in Mouse Brain Organotypic Cultures

Among the top ten causes of death in the United States, Alzheimer's disease (AD) is the only one that cannot be cured, prevented, or even slowed down at present. Significant efforts have been exerted in generating model systems to delineate the mechanism as well as establishing platforms for drug screening. In this study, a promising candidate model utilizing primary mouse brain organotypic (MBO) cultures is reported. For the first time, we have demonstrated that the MBO cultures exhibit increased blood brain barrier (BBB) permeability as shown by IgG leakage into the brain parenchyma, astrocyte activation as evidenced by increased expression of glial fibrillary acidic protein (GFAP), and neuronal damage-response as suggested by increased vimentin-positive neurons occur upon histamine treatment. Identical responses-a breakdown of the BBB, astrocyte activation, and neuronal expression of vimentin-were then demonstrated in brains from AD patients compared to age-matched controls, consistent with other reports. Thus, the histamine-treated MBO culture system may provide a valuable tool in combating AD.

Autoimmune Profiling Reveals Peroxiredoxin 6 as a Candidate Traumatic Brain Injury Biomarker

Autoimmune profiling in rats revealed the antioxidant enzyme, peroxiredoxin 6 (PRDX6), as a target for autoantibodies evoked in response to traumatic brain injury (TBI). Consistent with this proposal, immunohistochemical analysis of rat cerebral cortex demonstrated that PRDX6 is highly expressed in the perivascular space, presumably contained within astrocytic foot processes. Accordingly, an immunosorbent electrochemiluminescence assay was developed for investigating PRDX6 in human samples. PRDX6 was found to be measurable in human blood and highly expressed in human cerebral cortex and platelets. Circulating levels of PRDX6 were elevated fourfold over control values 4 to 24 h following mild-to-moderate TBI. These findings suggest that PRDX6 may serve as a biomarker for TBI and that autoimmune profiling is a viable strategy for the discovery of novel TBI biomarkers.

Hypothalamic-Pituitary Autoimmunity and Traumatic Brain Injury

Background: Traumatic brain injury (TBI) is a leading cause of secondary hypopituitarism in children and adults, and is responsible for impaired quality of life, disabilities and compromised development. Alterations of pituitary function can occur at any time after the traumatic event, presenting in various ways and evolving during time, so they require appropriate screening for early detection and treatment. Although the exact pathophysiology is unknown, several mechanisms have been hypothesized, including hypothalamic-pituitary autoimmunity (HP-A). The aim of this study was to systematically review literature on the association between HP-A and TBI-induced hypopituitarism. Major pitfalls related to the HP-A investigation were also discussed. Methods: The PubMed database was searched with a string developed for this purpose, without temporal or language limits, for original articles assessing the association of HP-A and TBI-induced hypopituitarism. Results: Three articles from the same group met the inclusion criteria. Anti-pituitary and anti-hypothalamic antibodies were detected using indirect immunofluorescence in a significant number of patients with acute and chronic TBI. Elevated antibody titer was associated with an increased risk of persistent hypopituitarism, especially somatotroph and gonadotroph deficiency, while no correlations were found with clinical parameters. Conclusion: HPA seems to contribute to TBI-induced pituitary damage, although major methodological issues need to be overcome and larger studies are warranted to confirm these preliminary data.

Autoantibodies in traumatic brain injury and central nervous system trauma

Despite the debilitating consequences and the widespread prevalence of brain trauma insults including spinal cord injury (SCI) and traumatic brain injury (TBI), there are currently few effective therapies for most of brain trauma sequelae. As a consequence, there has been a major quest for identifying better diagnostic tools, predictive models, and directed neurotherapeutic strategies in assessing brain trauma. Among the hallmark features of brain injury pathology is the central nervous systems' (CNS) abnormal activation of the immune response post-injury. Of interest, is the occurrence of autoantibodies which are produced following CNS trauma-induced disruption of the blood-brain barrier (BBB) and released into peripheral circulation mounted against self-brain-specific proteins acting as autoantigens. Recently, autoantibodies have been proposed as the new generation class of biomarkers due to their long-term presence in serum compared to their counterpart antigens. The diagnostic and prognostic value of several existing autoantibodies is currently being actively studied. Furthermore, the degree of direct and latent contribution of autoantibodies to CNS insult is still not fully characterized. It is being suggested that there may be an analogy of CNS autoantibodies secretion with the pathophysiology of autoimmune diseases, in which case, understanding and defining the role of autoantibodies in brain injury paradigm (SCI and TBI) may provide a realistic prospect for the development of effective neurotherapy. In this work, we will discuss the accumulating evidence about the appearance of autoantibodies following brain injury insults. Furthermore, we will provide perspectives on their potential roles as pathological components and as candidate markers for detecting and assessing CNS injury.

Alternative causes of hypopituitarism: traumatic brain injury, cranial irradiation, and infections

Hypopituitarism often remains unrecognized due to subtle clinical manifestations. Anterior pituitary hormone deficiencies may present as isolated or multiple and may be transient or permanent. Traumatic brain injury (TBI) is recognized as a risk factor for hypopituitarism, most frequently presenting with isolated growth hormone deficiency (GHD). Data analysis shows that about 15% of patients with TBI have some degree of hypopituitarism which if not recognized may be mistakenly ascribed to persistent neurologic injury and cognitive impairment. Identification of predictors for hypopituitarism after TBI is important, one of them being the severity of TBI. The mechanisms involve lesions in the hypothalamic-pituitary axis and inflammatory changes in the central nervous system (CNS). With time, hypopituitarism after TBI may progress or reverse. Cranial irradiation is another important risk factor for hypopituitarism. Deficiencies in anterior pituitary hormone secretion (partial or complete) occur following radiation damage to the hypothalamic-pituitary region, the severity and frequency of which correlate with the total radiation dose delivered to the region and the length of follow-up. These radiation-induced hormone deficiencies are irreversible and progressive. Despite numerous case reports, the incidence of hypothalamic-pituitary dysfunction following infectious diseases of the CNS has been underestimated. Hypopituitarism usually relates to the severity of the disease, type of causative agent (bacterial, TBC, fungal, or viral) and primary localization of the infection. Unrecognized hypopituitarism may be misdiagnosed as postencephalitic syndrome, while the presence of a sellar mass with suprasellar extension may be misdiagnosed as pituitary macroadenoma in a patient with pituitary abscess which is potentially a life-threatening disease.

A five year prospective investigation of anterior pituitary function after traumatic brain injury: is hypopituitarism long-term after head trauma associated with autoimmunity?

Traumatic brain injury (TBI) has been recently recognized as a common cause of pituitary dysfunction. However, there are not sufficient numbers of prospective studies to understand the natural history of TBI induced hypopituitarism. The aim was to report the results of five years' prospective follow-up of anterior pituitary function in patients with mild, moderate and severe TBI. Moreover, we have prospectively investigated the associations between TBI induced hypopituitarism and presence of anti-hypothalamus antibodies (AHA) and anti-pituitary antibodies (APA). Twenty five patients (20 men, five women) were included who were prospectively evaluated 12 months and five years after TBI, and 17 of them also had a third-year evaluation. Growth hormone (GH) deficiency is the most common pituitary hormone deficit at one, three, and five years after TBI. Although most of the pituitary hormone deficiencies improve over time, there were substantial percentages of pituitary hormone deficiencies at the fifth year (28% GH, 4% adrenocorticotropic hormone [ACTH], and 4% gonadotropin deficiencies). Pituitary dysfunction was significantly higher in strongly AHA- and APA-positive (titers ≥1/16) patients at the fifth year. In patients with mild and moderate TBI, ACTH and GH deficiencies may improve over time in a considerable number of patients but, although rarely, may also worsen over the five-year period. However in severe TBI, ACTH and GH status of the patients at the first year evaluation persisted at the fifth year. Therefore, screening pituitary function after TBI for five years is important, especially in patients with mild TBI. Moreover, close strong associations between the presence of high titers of APA and/or AHA and hypopituitarism at the fifth year were shown for the first time.

Sports-related chronic repetitive head trauma as a cause of pituitary dysfunction

Traumatic brain injury (TBI) is recognized as a cause of hypopituitarism even after mild TBI. Although over the past decade, a growing body of research has detailed neuroendocrine changes induced by TBI, the mechanisms and risk factors responsible for this pituitary dysfunction are still unclear. Around the world, sports-especially combative sports-are very popular. However, sports are not generally considered as a cause of TBI in most epidemiological studies, and the link between sports-related head trauma and hypopituitarism has not been investigated until recently. Thus, there is a paucity of data regarding this important concern. Because of the large number of young sports participants with near-normal life expectancy, the implications of undiagnosed or untreated postconcussion pituitary dysfunction can be dramatic. Understanding the pathophysiological mechanisms and risk factors of hypopituitarism caused by sports injuries is thus an important issue that concerns both medical staff and sponsors of sports. The aim of this paper was to summarize the best evidence for understanding the pathophysiological mechanisms and to discuss the current data and recommendations on sports-related head trauma as a cause of hypopituitarism.

Brain-reactive autoantibodies are nearly ubiquitous in human sera and may be linked to pathology in the context of blood-brain barrier breakdown

Previous studies have reported antibodies bound to cells in postmortem Alzheimer's disease (AD) brains, which are only rarely observed in the brains of healthy, age-matched controls. This implies that brain-reactive autoantibodies exist in the sera of AD individuals and can gain access to the brain interstitium. To investigate this possibility, we determined the prevalence of brain-reactive antibodies in sera from AD patients, patients with other neurodegenerative diseases, age-matched, non-demented controls and healthy younger individuals via immunohistochemistry and western blot analysis. Surprisingly, western analyses revealed that 92% of all human sera tested contain brain-reactive autoantibodies. When sera were used to probe western blots of human, pig, or rat brain membrane proteins, a number of comparably-sized protein targets were detected, suggesting cross-species reactivity. While the presence of brain-reactive autoantibodies was nearly ubiquitous in human sera, some autoantibodies appeared to be associated with age or disease. Furthermore, the intensity of antibody binding to brain tissue elements, especially the surfaces of neurons, correlated more closely to the serum's autoantibody profile than to age or the presence of neurodegenerative disease. However, while the blood-brain barrier (BBB) in control brains remained intact, BBB breakdown was common in AD brains. Results suggest a high prevalence of brain-reactive antibodies in human sera which, in the common context of BBB compromise, leads us to propose that these antibodies may contribute to the initiation and/or pathogenesis of AD and other neurodegenerative diseases.

Investigation of antihypothalamus and antipituitary antibodies in amateur boxers: is chronic repetitive head trauma-induced pituitary dysfunction associated with autoimmunity?

OBJECTIVE

Current data clearly demonstrate that sports-related chronic repetitive head trauma due to boxing might result in hypopituitarism. However, the mechanism of sports-related traumatic brain injury-induced pituitary dysfunction is still unclear. In order to understand whether autoimmune mechanisms could play a role in the pituitary dysfunction due to sports-related head trauma, we investigated the presence of antipituitary antibodies (APAs) and antihypothalamus antibodies (AHAs) in amateur boxers.

PATIENTS AND DESIGN

Sixty-one actively competing (n=44) or retired (n=17) male boxers (mean age, 26 years; range, 17-53) who had been evaluated regarding pituitary functions previously were included in the study. In all boxers and in 60 age/sex-similar normal controls, AHAs and APAs were investigated by an indirect immunofluorescence method.

RESULTS

AHAs were detected in 13 of 61 boxers (21.3%), and APAs were detected in 14 of 61 boxers (22.9%), but in none of the normal controls. Pituitary dysfunction was significantly higher in AHA-positive boxers (46.2%) than in AHA-negative boxers (10.4%) (P=0.003). There was a significant association between AHA positivity and hypopituitarism due to boxing (odds ratio: 7.37, 95% confidence interval 1.8-30.8). There was no significant association between APA positivity and hypopituitarism.

CONCLUSIONS

This study demonstrates for the first time the presence of AHAs and APAs in boxers who were exposed to sports-related head trauma. Moreover, the present investigation provides preliminary evidence that AHAs are associated with the development of pituitary dysfunction in boxers, thus suggesting that autoimmunity may have a role in the pathogenesis.

Antipituitary antibodies after traumatic brain injury: is head trauma-induced pituitary dysfunction associated with autoimmunity?

OBJECTIVE

Traumatic brain injury (TBI) is a devastating public health problem that may result in hypopituitarism. However, the mechanisms responsible for hypothalamic-pituitary dysfunction due to TBI are still unclear. Although the antibodies against neurons have been demonstrated in injured animal studies, investigations regarding the occurrence of antipituitary antibodies (APAs) in patients with TBI are lacking in the literature. In order to investigate whether autoimmune mechanisms could play a role in the pituitary dysfunction after TBI, we have planned this study aimed at investigating the presence of APA at the third year of TBI and association between the TBI-induced hypopituitarism and APA.

PATIENTS AND DESIGN

Twenty-nine (25 males and 4 females; age 36.5+/-2.3 years) patients who had completed a 3-year follow-up after TBI were included in the present study. APA and pituitary function were evaluated in all the patients 3 years after TBI; moreover, APAs were tested also in sera of 60 age-/sex-matched normal controls. The APAs were investigated by an indirect immunofluorescence method. Results APAs were detected in 13 out of the 29 TBI patients (44.8%), but in none of the normal controls. Pituitary dysfunction development ratio was significantly higher in APA-positive patients (46.2%) when compared with APA-negative ones (12.5%; P=0.04). There was a significant association between APA positivity and hypopituitarism due to TBI (odds ratio: 2.25, 95% confidence intervals 1.1-4.6). Moreover, there was a significant positive correlation (r=0.74, P=0.004) between APA titer ratio and peak GH response to GHRH+GH related peptide (GHRP)-6 test, suggesting that high APA titers were associated with low GH response to GHRH+GHRP-6 test.

CONCLUSIONS

This study shows for the first time the presence of the APA in TBI patients 3 years after head trauma. Moreover, present investigation indicates preliminary evidence that APA may be associated with the development of TBI-induced pituitary dysfunction, thus suggesting that autoimmunity may contribute in the development of TBI-induced hypopituitarism. The presence of the association between APA and TBI-induced hypopituitarism may provide a new point of view in this field and promote further clinical and experimental studies.

Spinal cord injury triggers systemic autoimmunity: evidence for chronic B lymphocyte activation and lupus-like autoantibody synthesis

Clinical and experimental data indicate that spinal cord injury (SCI) elicits pathological T-cell responses. Implicit in these data, but poorly understood, is that B lymphocytes (B cells) also contribute to the delayed pathophysiology of spinal trauma. Here, for the first time, we show that experimental spinal contusion injury elicits chronic systemic and intraspinal B cell activation with the emergence of a B cell-dependent organ-specific and systemic autoimmune response. Specifically, using sera from spinal cord injured mice, immunoblots reveal oligoclonal IgG reactivity against multiple CNS proteins. We also show SCI-induced synthesis of autoantibodies that bind nuclear antigens including DNA and RNA. Elevated levels of anti-DNA antibodies are a distinguishing feature of systemic lupus erythematosus and, via their ability to cross-react with neuronal antigens, can cause neuropathology. We show a similar pathologic potential for the autoantibodies produced after SCI. Thus, mammalian SCI produces marked dysregulation of B cell function (i.e. autoimmunity) with pathological potential.

IgG entry and deposition are components of the neuroimmune response in Batten disease

Patients and a mouse model of Batten disease, the juvenile form of neuronal ceroid lipofuscinosis (JNCL), raise autoantibodies against GAD65 and other brain-directed antigens. Here we investigate the adaptive component of the neuroimmune response. Cln3(-/-) mice have autoantibodies to GAD65 in their cerebrospinal fluid and elevated levels of brain bound immunoglobulin G (IgG). IgG deposition was found within human JNCL autopsy material, a feature that became more evident with increased age in Cln3(-/-) mice. The lymphocyte infiltration present in human and murine JNCL occurred late in disease progression, and was not capable of central/intrathecal IgG production. In contrast, we found evidence for an early systemic immune dysregulation in Cln3(-/-) mice. In addition evidence for a size-selective breach in the blood-brain barrier integrity in these mice suggests that systemically produced autoantibodies can access the JNCL central nervous system and contribute to a progressive inflammatory response.

Autoreactive antibodies against neurons and basal lamina found in serum following experimental brain contusion in rats

BACKGROUND

Brain trauma is a risk factor for delayed CNS degeneration which may be attenuated by anti-inflammatory treatment. CNS injuries may cause anti-brain reactivity. This study was undertaken to analyze the pattern of delayed post-traumatic anti-brain immunity in experimental brain contusion.

METHOD

Adult Sprague-Dawley and Lewis rats were subjected to experimental brain contusions. For B-cell investigations, serum was obtained from contused, control and naïve rats, and used for immunohistochemistry on slices of rat brains to first detect autoreactive IgG and IgM antibodies in rat serum. Secondly, anti-rat IgG and IgM antibodies were used to search for auto-antibodies already bound to the brain tissue. Double staining with rat-serum and NeuN or anti-GFAP antibody was used to detect anti-neuronal and anti-astrocytic antibodies, respectively. For T-cell reactivity, cells from brains and cervical lymph nodes of rats were used in FACS analysis and elispot with MBP and MOG stimulation.

FINDINGS

Anti-vascular basal lamina IgG antibodies were detected at three months in 6/8 rats, following experimental contusion. Anti-neuronal IgG antibodies were detected 2 weeks after experimental contusion and sham surgery, while naïve controls were negative. Individual rats showed a prolonged response, or an anti-astrocytic staining. Tissue bound anti-self IgG or IgM was not detected in the brain tissue. Anti-MBP or anti-MOG T-cell responses were not detectable.

CONCLUSIONS

Experimental brain trauma and to some degree even sham surgery lead to an individually variable pattern of specific anti-brain reactive B-cells, while a T-cell response did not seem to be a consequence of moderate experimental contusion. The mere presence of anti brain-antibodies may be epiphenomenal, but could also be pathogenic for delayed degeneration. It is reasonable to regard the presence of an actual anti-brain reactivity as a potential threat to brain tissue integrity.

A possible role for humoral immunity in the pathogenesis of Parkinson's disease

The pathogenesis of idiopathic Parkinson's disease is unknown, but nigral degeneration and depigmentation are associated with microglial inflammation and anti-inflammatory medications appear to protect against the disease. The possibility that humoral immunity may play a role in initiating or regulating the inflammation has been suggested by experimental studies triggering dopamine cell death using a variety of transfer strategies and the observation of CD8+ T lymphocytes and complement in the nigra in Parkinson's disease. We analysed the association between degeneration and humoral immune markers in brain tissue of patients with idiopathic (n = 13) or genetic (n = 2 with alpha-synuclein and n = 1 with parkin mutations) Parkinson's disease and controls without neurological disease (n = 12) to determine the humoral immune involvement in Parkinson's disease. Formalin-fixed tissue samples from the substantia nigra and primary visual cortex for comparison were stained for alpha-synuclein, major histocompatibility complex II (HLA), immunoglobulin M (IgM), immunoglobulin G (IgG), IgG subclasses 1-4 and IgG receptors FcgammaR I-III. Antigen retrieval and both single immunoperoxidase and double immunofluorescence procedures were employed to determine the cell types involved and their pattern and semiquantitative densities. Significant dopamine neuron loss occurred in all patients with Parkinson's disease, negatively correlating with disease duration (r = -0.76, P = 0.002). Although all patients had increased inflammatory HLA immunopositive microglia, the degree of inflammation was similar throughout the disease (r = 0.08, P = 0.82). All patients with Parkinson's disease had IgG binding on dopamine neurons but not IgM binding. Lewy bodies were strongly immunolabelled with IgG. A mean 30 +/- 12% of dopamine nigral neurons were immunoreactive for IgG in Parkinson's disease with the proportion of IgG immunopositive neurons negatively correlating with the degree of cell loss in the substantia nigra (r = -0.67, P < 0.0001) and positively correlating with the number of HLA immunopositive microglia (r = 0.51, P = 0.01). Most neuronal IgG was the IgG1 subclass with some IgG3 and less IgG2 also found in the damaged substantia nigra. The high affinity activating IgG receptor, FcgammaRI, was expressed on nearby activated microglia. The low affinity activating IgG receptor, FcgammaRIII was expressed on cells morphologically resembling lymphocytes, whereas immunoreactivity for the inhibitory IgG receptor FcgammaRII was absent in all cases. This pattern of humoral immune reactivity is consistent with an immune activation of microglia leading to the targeting of dopamine nigral neurons for destruction in both idiopathic and genetic cases of Parkinson's disease.

Humoral immunity in brain aging and Alzheimer's disease

Although the contribution of inflammatory processes in the etiology of late-onset Alzheimer's disease (AD) has been suspected for years, most studies were confined to the analysis of cell-mediated immunological reactions thought to represent an epiphenomenon of AD lesion development. Based on the traditional view of the "immunological privilege" of the brain, which excludes a direct access of human immunoglobulins (Ig) to the central nervous system under normal conditions, little attention has been paid to a possible role of humoral immunity in AD pathogenesis. In the first part of this review, we summarize evidences for a blood-brain barrier (BBB) dysfunction in this disorder and critically comment on earlier observations supporting the presence of anti-brain autoantibodies and immunoglobulins (Ig) in AD brains. Current concepts regarding the Ig turnover in the central nervous system and the mechanisms of glial and neuronal Fc receptors activation are also discussed. In the second part, we present new ex vivo and in vitro data suggesting that human immunoglobulins can interact with tau protein and alter both the dynamics and structural organization of microtubules. Subsequent experiments needed to test this new working hypothesis are addressed at the end of the review.

Epilepsy and the immune system: is there a link?

The concept that the immune system plays a role in the epileptogenic process of some epileptic syndromes was first proposed more than 20 years ago. Since then, numerous studies have reported on the existence of a variety of immunological alterations in epileptic patients, on the observation of favourable responses of refractory epilepsy syndromes to immunomodulatory treatment, and on the association of certain well-known immune-mediated disease states with epilepsy. This review comprehensively recapitulates the currently available evidence supporting or arguing against the possible involvement of the immune system in the pathogenesis of certain types of epilepsy. It is concluded that an abundance of facts is in support of this concept and that further studies should be directed at substantiating the pathogenic significance of (auto)immune responses in certain types of epilepsy. Current progress in the functional and molecular immunological research techniques will indisputably contribute to the elucidation of this link.

Genetic dissection of systemic autoimmune disease in Nrf2-deficient mice

Systemic lupus erythematosus (SLE) is an autoimmune disorder with immune-complex deposition that affects multiple organs. Previous studies have suggested the involvement of oxidative stress and apoptosis in SLE, but no clear link to etiology has been established. Here we show that mice deficient in a transcription factor responsible for controlling the expression of numerous detoxification and antioxidant genes develop an autoimmune disease with multiple organ pathologies that closely resembles human SLE. Aged female mice with a knockout of nuclear factor, erythroid-derived 2, like 2 (nrf2) are prone to develop antibodies against double-stranded DNA and the Smith antigen as well as IgG, IgM, and C3 deposition in kidney, liver, heart, and brain. Prior to the development of autoimmune antibodies and organ pathology, oxidative damage occurs in the liver and kidney as indicated by the increased levels of the DNA oxidation marker 8-hydroxydeoxyguanosine and the later increase in the lipid peroxidation product malondialdehyde. Gene expression profiles demonstrate an early decrease in numerous antioxidant and detoxification genes in the livers and altered levels of cytokines and T and B cell-specific genes in the spleens of nrf2 knockout mice. These data strongly suggest that a deficiency in detoxification and increased oxidative stress can result in the development of a systemic autoimmune disease.