Infections in the Developing Brain: The Role of the Neuro-Immune Axis

MHC class I and II expression and induction in oligodendrocytes varies with age

Oligodendroglia expressing major histocompatibility complex (MHC) molecules have become of central interest in multiple sclerosis (MS) research, but their role in aging is still being elucidated. Using MHC class I and II reporter mice, we compared oligodendroglial MHC expression in neonatal, young adult (8-16 weeks), and aging (52 weeks) mice at baseline and after stereotactic delivery of AAV-GFAP-IFNγ. We found that MHC class I-expressing oligodendroglia were present in both the naïve brain and spinal cord, while MHC class II-expressing oligodendroglia were seen only in the spinal cord of aging mice at baseline. After AAV injection, MHC expression in oligodendroglia increased, recapitulating pathology seen in MS mouse models and in MS post-mortem tissue. After IFNγ-AAV injection, the abundance of MHC class I-expressing oligodendroglia did not vary with age, whereas MHC class II-expressing oligodendroglia were more abundant in aging mice than neonatal and young adult mice. Our results suggest that MHC class II-expressing oligodendroglia are more prevalent with aging, which may contribute to the mechanisms underlying progressive MS and other age-related neurodegenerative diseases with central nervous system inflammation.

Age-Stratified Treg Responses During Viral Infections of the Central Nervous System: A Literature Review

Regulatory T cells (Tregs) play a vital role in limiting inflammation and resolving the immune response after a viral infection. Within the central nervous system (CNS), Tregs are especially important for the protection of neurons, which have limited regenerative capacity, and the preservation of myelin sheaths, which support neuronal function and survival. Nevertheless, viral infections of the CNS often result in enduring neurological dysfunction, especially in more vulnerable age groups such as newborns and the elderly. Although it is appreciated that Treg activity changes with age, it is unclear how these age-dependent changes impact viral CNS infections. In this review, we explore Treg development over the life of the host and discuss evidence for age-dependent Treg responses to peripheral viral infections. We also discuss the CNS-specific roles of Tregs, where both immunomodulatory and neuroprotective functions can contribute to preservation of brain cells. Finally, we examine the current evidence for Treg activity in neurotropic infections in the context of age, and highlight gaps in our understanding of Treg function in younger and older hosts. Overall, a better understanding of age-dependent Treg activity in the CNS may reveal opportunities for therapeutic interventions tailored to the most vulnerable ages.

ISMRM Clinical Focus Meeting 2023: "Imaging the Fire in the Brain"

Set during the Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM), the "Clinical Focus Meeting" (CFM) aims to bridge the gap between innovative magnetic resonance imaging (MRI) scientific research and daily patient care. This initiative is dedicated to maximizing the impact of MRI technology on healthcare outcomes for patients. At the 2023 Annual Meeting, clinicians and scientists from across the globe were invited to discuss neuroinflammation from various angles (entitled "Imaging the Fire in the Brain"). Topics ranged from fundamental mechanisms and biomarkers of neuroinflammation to the role of different contrast mechanisms, including both proton and non-proton techniques, in brain tumors, autoimmune disorders, and pediatric neuroinflammatory diseases. Discussions also delved into how systemic inflammation can trigger neuroinflammation and the role of the gut-brain axis in causing brain inflammation. Neuroinflammation arises from various external and internal factors and serves as a vital mechanism to mitigate tissue damage and provide neuroprotection. Nonetheless, excessive neuroinflammatory responses can lead to significant tissue injury and subsequent neurological impairments. Prolonged neuroinflammation can result in cellular apoptosis and neurodegeneration, posing severe consequences. MRI can be used to visualize these consequences, by detecting blood-brain barrier damage, characterizing brain lesions, quantifying edema, and identifying specific metabolites. It also facilitates monitoring of chronic changes in both the brain and spinal cord over time, potentially leading to better patient outcomes. This paper represents a summary of the 2023 CFM, and is intended to guide the enthusiastic MR user to several key and novel sequences that MRI offers to image pathophysiologic processes underlying acute and chronic neuroinflammation. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

Clinical Manifestation of Arboviruses in Paediatrics

Arboviral infections in paediatric populations present unique challenges due to distinct pathophysiological mechanisms influenced by developmental and immunological differences. Commonly implicated arboviruses include dengue virus (DENV), Zika virus (ZIKV), chikungunya virus (CHIKV), West Nile virus (WNV), and yellow fever virus (YFV). These viruses exhibit specific tropisms, targeting organs such as the central nervous system (CNS), liver, and vasculature. Immune responses in children, characterised by an underdeveloped adaptive system and enhanced innate immunity, can exacerbate inflammation and increase susceptibility to severe outcomes such as dengue hemorrhagic fever (DHF), congenital Zika syndrome (CZS), and neuroinvasive complications. Maternal antibodies, antibody-dependent enhancement (ADE), and immature barriers, such as the blood-brain barrier, further contribute to disease severity. This review highlights the virological and immunological nuances of arboviral pathophysiology in paediatric patients, emphasising the need for age-specific diagnostic, therapeutic, and preventive strategies to mitigate the burden of these infections.

Risk of psychiatric neurodevelopmental disorders after meningitis in childhood: a nationwide, population-based cohort study

BACKGROUND

Few studies have investigated the risk of psychiatric neurodevelopmental disorders (PNDD) after childhood meningitis.

METHODS

Nationwide population-based cohort study (Denmark, 1995-2021) of children with positive cerebrospinal fluid for bacteria or enterovirus, stratified on age as young infants (0 to <90 days, n = 637) or older children (≥90 days to <17 years, n = 1,218). We constructed a comparison cohort from the general population (n = 18,550), and cohorts of siblings of participants. As risk estimates of PNDD we calculated age- and sex-adjusted hazard ratios (aHRs) with 95% confidence intervals (95%CI).

RESULTS

Children with bacterial meningitis had increased risks of PNDD, especially learning and intellectual developmental disorders (young infants: aHR 4.2, 95%CI: 2.4-7.1; older children: aHR 1.5, 95%CI: 1.0-2.3), attention deficit disorder (ADHD) (young infants: aHR 2.8, 95%CI: 1.5-5.2; older children: 1.4, 95%CI: 0.9-2.2) and redemption of ADHD medication (young infants: aHR 2.2, 95%CI: 1.0-4.7; older children: 1.5, 95%CI: 1.0-2.3). Young infants with bacterial meningitis additionally had increased risks of autism spectrum disorders (aHR 1.9, 95%CI: 0.9-4.1) and behavioural and emotional disorders (aHR 2.0, 95%CI: 1.0-3.9). In young infants, the excess risk of PNDD was especially observed in premature children. Siblings of older children with bacterial meningitis also had increased risks of PNDD. Children with enteroviral meningitis at any age did not have increased risks of PNDD or redemption of ADHD medication.

CONCLUSIONS

Bacterial meningitis in childhood is associated with subsequent diagnosis of PNDD, while enteroviral meningitis is not. The association appears to be partly explained by prematurity and familial and socioeconomic factors.

Complex Neuroimmune Involvement in Neurodevelopment: A Mini-Review

It is increasingly evident that cells and molecules of the immune system play significant roles in neurodevelopment. As perinatal infection is associated with the development of neurodevelopmental disorders, previous research has focused on demonstrating that the induction of neuroinflammation in the developing brain is capable of causing neuropathology and behavioral changes. Recent studies, however, have revealed that immune cells and molecules in the brain can influence neurodevelopment without the induction of overt inflammation, identifying neuroimmune activities as integral parts of normal neurodevelopment. This mini-review describes the shift in literature that has moved from emphasizing the intrusion of inflammatory events as a main culprit of neurodevelopmental disorders to evaluating the deviation of the normal neuroimmune activities in neurodevelopment as a potential pathogenic mechanism.

Systemic immune responses after ischemic stroke: From the center to the periphery

Ischemic stroke is a leading cause of disability and death. It imposes a heavy economic burden on individuals, families and society. The mortality rate of ischemic stroke has decreased with the help of thrombolytic drug therapy and intravascular intervention. However, the nerve damage caused by ischemia-reperfusion is long-lasting and followed by multiple organ dysfunction. In this process, the immune responses manifested by systemic inflammatory responses play an important role. It begins with neuroinflammation following ischemic stroke. The large number of inflammatory cells released after activation of immune cells in the lesion area, along with the deactivated neuroendocrine and autonomic nervous systems, link the center with the periphery. With the activation of systemic immunity and the emergence of immunosuppression, peripheral organs become the second “battlefield” of the immune response after ischemic stroke and gradually become dysfunctional and lead to an adverse prognosis. The purpose of this review was to describe the systemic immune responses after ischemic stroke. We hope to provide new ideas for future research and clinical treatments to improve patient outcomes and quality of life.

Identifying Rare Genetic Variants of Immune Mediators as Risk Factors for Autism Spectrum Disorder

Autism spectrum disorder (ASD) affects more than 1% of children, and there is no viable pharmacotherapeutic agent to treat the core symptoms of ASD. Studies have shown that children with ASD show changes in their levels of immune response molecules. Our previous studies have shown that ASD is more common in children with folate receptor autoantibodies. We also found that children with ASD have abnormal gut immune function, which was characterized by a significant increase in the content of immunoglobulin A and an increase in gut-microbiota-associated epitope diversity. These studies suggest that the immune mechanism plays an important role in the occurrence of ASD. The present study aims to systematically assess gene mutations in immune mediators in patients with ASD. We collected genetic samples from 72 children with ASD (2−12 years old) and 107 healthy controls without ASD (20−78 years old). We used our previously-designed immune gene panel, which can capture cytokine and receptor genes, the coding regions of MHC genes, and genes of innate immunity. Target region sequencing (500×) and bioinformatics analytical methods were used to identify variants in immune response genes associated with patients with ASD. A total of 4 rare variants were found to be associated with ASD, including HLA-B: p.A93G, HLA-DQB1: p.S229N, LILRB2: p.R322H, and LILRB2: c.956-4C>T. These variants were present in 44.44% (32/72) of the ASD patients and were detected in 3.74% (4/107) of the healthy controls. We expect these genetic variants will serve as new targets for the clinical genetic assessment of ASD, and our findings suggest that immune abnormalities in children with ASD may have a genetic basis.