Autoantibodies: double agents in human disease

The Immune System as a Therapeutic Target for Alzheimer’s Disease

Alzheimer’s disease (AD) is a heterogeneous neurodegenerative disorder and is the most common cause of dementia. Furthermore, aging is considered the most critical risk factor for AD. However, despite the vast amount of research and resources allocated to the understanding and development of AD treatments, setbacks have been more prominent than successes. Recent studies have shown that there is an intricate connection between the immune and central nervous systems, which can be imbalanced and thereby mediate neuroinflammation and AD. Thus, this review examines this connection and how it can be altered with AD. Recent developments in active and passive immunotherapy for AD are also discussed as well as suggestions for improving these therapies moving forward.

Discovery of Novel Markers for Identifying Cognitive Decline Using Neuron-Derived Exosomes

Alzheimer's disease (AD), the predominant cause of late-life dementia, has a multifactorial etiology. Since there are few therapeutic options for symptomatic AD, research is increasingly focused on the identification of pre-symptomatic biomarkers. Recently, evaluation of neuron-derived exosomal markers has emerged as a promising novel approach for determining neuronal dysfunction. We aimed to identify novel neuron-derived exosomal markers that signify a transition from normal aging to Mild Cognitive Impairment (MCI) and then to clinically established AD, a sequence we refer to as AD progression. By using a Tandem Mass Tag-based quantitative proteomic approach, we identified a total of 360 neuron-derived exosomal proteins. Subsequent fuzzy c-means clustering revealed two clusters of proteins displaying trends of gradually increasing/decreasing expression over the period of AD progression (normal to MCI to AD), both of which were mainly involved in immune response-associated pathways, proteins within these clusters were defined as bridge proteins. Several differentially expressed proteins (DEPs) were identified in the progression of AD. The intersections of bridge proteins and DEPs were defined as key proteins, including C7 (Complement component 7), FERMT3 (Fermitin Family Member 3), CAP1 (Adenylyl cyclase-associated protein 1), ENO1 (Enolase 1), and ZYX (Zyxin), among which the expression patterns of C7 and ZYX were almost consistent with the proteomic results. Collectively, we propose that C7 and ZYX might be two novel neuron-derived exosomal protein markers, expression of which might be used to evaluate cognitive decline before a clinical diagnosis of AD is warranted.

Blood Biomarkers for Traumatic Brain Injury: A Quantitative Assessment of Diagnostic and Prognostic Accuracy

Blood biomarkers have been explored for their potential to provide objective measures in the assessment of traumatic brain injury (TBI). However, it is not clear which biomarkers are best for diagnosis and prognosis in different severities of TBI. Here, we compare existing studies on the discriminative abilities of serum biomarkers for four commonly studied clinical situations: detecting concussion, predicting intracranial damage after mild TBI (mTBI), predicting delayed recovery after mTBI, and predicting adverse outcome after severe TBI (sTBI). We conducted a literature search of publications on biomarkers in TBI published up until July 2018. Operating characteristics were pooled for each biomarker for comparison. For detecting concussion, 4 biomarker panels and creatine kinase B type had excellent discriminative ability. For detecting intracranial injury and the need for a head CT scan after mTBI, 2 biomarker panels, and hyperphosphorylated tau had excellent operating characteristics. For predicting delayed recovery after mTBI, top candidates included calpain-derived αII-spectrin N-terminal fragment, tau A, neurofilament light, and ghrelin. For predicting adverse outcome following sTBI, no biomarker had excellent performance, but several had good performance, including markers of coagulation and inflammation, structural proteins in the brain, and proteins involved in homeostasis. The highest-performing biomarkers in each of these categories may provide insight into the pathophysiologies underlying mild and severe TBI. With further study, these biomarkers have the potential to be used alongside clinical and radiological data to improve TBI diagnostics, prognostics, and evidence-based medical management.

Autoantibodies against N-methyl-d-aspartate receptor 1 in health and disease

Purpose of review

Humoral autoimmunity has gained highest interest in neurology and psychiatry. Despite numerous recent articles on this hot topic, however, the biological significance of natural autoantibodies (AB) and the normal autoimmune repertoire of mammals remained quite obscure. AB may contribute to disorder-relevant phenotypes and are even believed to induce diseases themselves, but the circumstances under which AB become pathogenic are not fully understood. This review will focus on the highly frequent AB against the N-methyl-d-aspartate receptor 1 (NMDAR1-AB) as an illustrating example and provide a critical overview of current work (please note that the new nomenclature, GluN1, is disregarded here for consistency with the AB literature). In particular, it will demonstrate how little is known at this point and how many conclusions are drawn based on small numbers of individuals, fragmentary experimental approaches or missing controls.

Recent findings

NMDAR1-AB were investigated by clinicians world-wide with numerous small studies and case reports appearing yearly. Many publications were on ‘anti-NMDAR encephalitis’ cases or tried to separate those from other NMDAR1-AB associated conditions. Original exclusivity claims (e.g. electroencephalogram, EEG or functional magnetic resonance imaging, fMRI findings) turned out not to be exclusive for ‘anti-NMDAR encephalitis’. Systematic analyses of representative NMDAR1-AB positive sera of all immunoglobulin (Ig) classes showed comparable distribution of different epitopes, often polyspecific/polyclonal, across health and disease. Sophisticated imaging tools provided findings on synapse trafficking changes induced by NMDAR1-AB from psychotic subjects but still lack epitope data to support any claimed disorder link. Persistently high titers of NMDAR1-AB (IgG) in immunized mice with open blood–brain barrier (BBB)-induced psychosis-like symptoms but failed to induce inflammation in the brain. Knowledge on peripheral NMDAR, for example in the immune system, and on potential inducers of NMDAR1-AB is only slowly increasing.

Summary

The present knowledge on the (patho) physiological role of NMDAR1-AB is very limited and still characterized by adamant rumors. Much more experimental work and more solid and informative clinical reports, including large numbers of subjects and adequate control groups, follow-up investigations and interdisciplinary approaches will be necessary to obtain a better understanding of the significance of humoral autoimmunity in general (in focus here: NMDAR1-AB) and its disease-relevance in particular.

Peripheral immune system in aging and Alzheimer's disease

Alzheimer's disease (AD) represents an urgent public health mandate. AD is no longer considered a neural-centric disease; rather, a plethora of recent studies strongly implicate a critical role played by neuroinflammation in the pathogeneses of AD and other neurodegenerative conditions. A close functional connection between the immune system and central nervous system is increasingly recognized. In late-onset AD, aging represents the most significant risk factor. Here, from an immunological perspective, we summarize the prominent molecular and cellular changes in the periphery of aging individuals and AD patients. Moreover, we review the knowledge gained in the past several years that implicate specific arms of the peripheral immune system and other types of immune responses in modulating AD progression. Taken together, these findings collectively emphasize a dynamic role of a concert of brain-extrinsic, peripheral signals in the aging and degenerative processes in the CNS. We believe that a systematic view synthesizing the vast amounts of existing results will help guide the development of next-generation therapeutics and inform future directions of AD investigation.

Age-dependent increase of blood-brain barrier permeability and neuron-binding autoantibodies in S100B knockout mice

S100B is a calcium-sensor protein that impacts multiple signal transduction pathways. It is widely considered to be an important biomarker for several neuronal diseases as well as blood-brain barrier (BBB) breakdown. In this report, we demonstrate a BBB deficiency in mice that lack S100B through detection of leaked Immunoglobulin G (IgG) in the brain parenchyma. IgG leaks and IgG-binding to selected neurons were observed in S100B knockout (S100BKO) mice at 6 months of age but not at 3 months. By 9 months, IgG leaks persisted and the density of IgG-bound neurons increased significantly. These results reveal a chronic increase in BBB permeability upon aging in S100BKO mice for the first time. Moreover, coincident with the increase in IgG-bound neurons, autoantibodies targeting brain proteins were detected in the serum via western blots. These events were concurrent with compromise of neurons, increase of activated microglia and lack of astrocytic activation as evidenced by decreased expression of microtubule-associated protein type 2 (MAP2), elevated number of CD68 positive cells and unaltered expression of glial fibrillary acidic protein (GFAP) respectively. Results suggest a key role for S100B in maintaining BBB functional integrity and, further, propose the S100BKO mouse as a valuable model system to explore the link between chronic functional compromise of the BBB, generation of brain-reactive autoantibodies and neuronal dysfunctions.

The significance of autoantibodies to DFS70/LEDGFp75 in health and disease: integrating basic science with clinical understanding

Antinuclear autoantibodies (ANAs) displaying the nuclear dense fine speckled immunofluorescence (DFS-IIF) pattern in HEp-2 substrates are commonly observed in clinical laboratory referrals. They target the dense fine speckled autoantigen of 70 kD (DFS70), most commonly known as lens epithelium-derived growth factor p75 (LEDGFp75). Interesting features of these ANAs include their low frequency in patients with systemic autoimmune rheumatic diseases (SARD), elevated prevalence in apparently healthy individuals, IgG isotype, strong trend to occur as the only ANA specificity in serum, and occurrence in moderate to high titers. These autoantibodies have also been detected at varied frequencies in patients with diverse non-SARD inflammatory and malignant conditions such as atopic diseases, asthma, eye diseases, and prostate cancer. These observations have recently stimulated vigorous research on their clinical and biological significance. Some studies have suggested that they are natural, protective antibodies that could serve as biomarkers to exclude a SARD diagnosis. Other studies suggest that they might be pathogenic in certain contexts. The emerging role of DFS70/LEDGFp75 as a stress protein relevant to human acquired immunodeficiency syndrome, cancer, and inflammation also points to the possibility that these autoantibodies could be sensors of cellular stress and inflammation associated with environmental factors. In this comprehensive review, we integrate our current knowledge of the biology of DFS70/LEDGFp75 with the clinical understanding of its autoantibodies in the contexts of health and disease.