Temporal patterns of microglial activation in white matter following experimental mild traumatic brain injury: a systematic literature review.

Mild traumatic brain injuries (mTBIs) are a prevalent form of injury that can result in persistent neurological impairments. Microglial activation has become increasingly recognized as a key process regulating the pathology of white matter in a wide range of brain injury and disease contexts. As white matter damage is known to be a major contributor to the impairments that follow mTBI, microglia have rightfully become a common target of investigation for the development of mTBI therapies and biomarkers. Recent work has demonstrated that the efficacy of microglial manipulation as a therapeutic intervention following injury or disease is highly time-sensitive, emphasizing the importance of advancing our understanding of the dynamics of post-mTBI microglial activation from onset to resolution. Current reporting of microglial activation in experimental studies of mTBI is non-standardized, which has limited our ability to identify concrete patterns of post-mTBI microglial activation over time. In this review, we examine preclinical studies of mTBI that report on microglial activation in white matter regions to summarize our current understanding of these patterns. Specifically, we summarize timecourses of post-mTBI microglial activation in white matter regions of the brain, identify factors that influence this activation, examine the temporal relationship between microglial activation and other post-mTBI assessments, and compare the relative sensitivities of various methods for detecting microglial activation. While the lack of replicated experimental conditions has limited the extent of conclusions that can confidently be drawn, we find that microglia are activated over a wide range of timecourses following mTBI and that microglial activation is a long-lasting outcome of mTBI that may resolve after most typical post-mTBI assessments, with the exception of those measuring oligodendrocyte lineage cell integrity. We identify several understudied parameters of post-mTBI microglial activation in white matter, such as the inclusion of female subjects. This review summarizes our current understanding of the progression of microglial activation in white matter structures following experimental mTBI and offers suggestions for important future research directions.

Elevated complement mediator levels in endothelial-derived plasma exosomes implicate endothelial innate inflammation in diminished brain function of aging humans.

We test the hypothesis that endothelial cells adopt an inflammatory phenotype in functionally intact aged human subjects with radiographic evidence of white matter hyperintensity (WMH) suggestive of small cerebrovascular disease. Components of all three complement effector pathways and regulatory proteins were quantified in extracts of plasma endothelial-derived exosomes (EDE) of 11 subjects (age 70-82) with and 15 without evidence of WMH on MRI. Group differences and associations with plasma markers of immune activation (IL6, ICAM1), cognition and neuroimaging were calculated via regression modelling. EDE complement factors within the alternative and classical pathways were found to be higher and regulatory proteins lower in subjects with WMH. EDE levels of some complement components demonstrated significant associations with cognitive slowing and elevated systolic blood pressure. The inhibitor of the membrane attack complex, CD46, showed a significant positive association with cerebral grey matter volume. Plasma inflammatory markers, IL6 and ICAM1, were positively associated with EDE levels of several complement components. These findings provide the first in vivo evidence of the association of endothelial cell inflammation with white matter disease, age-associated cognitive changes, and brain degeneration in functionally normal older individuals. Future endothelial biomarker development may permit recognition of early or preclinical stages of vascular contributions to cognitive impairment and dementia.

Nanoparticulate matter exposure results in white matter damage and an inflammatory microglial response in an experimental murine model.

Exposure to ambient air pollution has been associated with white matter damage and neurocognitive decline. However, the mechanisms of this injury are not well understood and remain largely uncharacterized in experimental models. Prior studies have shown that exposure to particulate matter (PM), a sub-fraction of air pollution, results in neuroinflammation, specifically the upregulation of inflammatory microglia. This study examines white matter and axonal injury, and characterizes microglial reactivity in the corpus callosum of mice exposed to 10 weeks (150 hours) of PM. Nanoscale particulate matter (nPM, aerodynamic diameter ≤200 nm) consisting primarily of traffic-related emissions was collected from an urban area in Los Angeles. Male C57BL/6J mice were exposed to either re-aerosolized nPM or filtered air for 5 hours/day, 3 days/week, for 10 weeks (150 hours; n = 18/group). Microglia were characterized by immunohistochemical double staining of ionized calcium-binding protein-1 (Iba-1) with inducible nitric oxide synthase (iNOS) to identify pro-inflammatory cells, and Iba-1 with arginase-1 (Arg) to identify anti-inflammatory/ homeostatic cells. Myelin injury was assessed by degraded myelin basic protein (dMBP). Oligodendrocyte cell counts were evaluated by oligodendrocyte transcription factor 2 (Olig2). Axonal injury was assessed by axonal neurofilament marker SMI-312. iNOS-expressing microglia were significantly increased in the corpus callosum of mice exposed to nPM when compared to those exposed to filtered air (2.2 fold increase; p<0.05). This was accompanied by an increase in dMBP (1.4 fold increase; p<0.05) immunofluorescent density, a decrease in oligodendrocyte cell counts (1.16 fold decrease; p<0.05), and a decrease in neurofilament SMI-312 (1.13 fold decrease; p<0.05) immunofluorescent density. Exposure to nPM results in increased inflammatory microglia, white matter injury, and axonal degradation in the corpus callosum of adult male mice. iNOS-expressing microglia release cytokines and reactive oxygen/ nitrogen species which may further contribute to the white matter damage observed in this model.

Autoimmune glial fibrillary acidic protein astrocytopathy mimicking acute disseminated encephalomyelitis: A case report.

INTRODUCTION: Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is an increasingly recognized type of steroid-responsive autoimmune disease of the nervous system. Defined in 2016, it is associated with the presence of anti-GFAP immunoglobulinG in the serum or cerebrospinal fluid (CSF) of affected patients. PATIENT CHARACTERISTICS: Herein, we report a case of acute neurological symptoms, including headache, fever, confusion, and paralysis of the lower extremities. CSF analysis revealed lymphocytic pleocytosis and elevated protein levels, indicating acute disseminated encephalomyelitis, and the patient was given immunotherapy. Cranial magnetic resonance imaging showed multifocal T2/fluid-attenuated inversion recovery hyperintense signal changes in the periventricular white matter, and electromyography testing showed changes consistent with severe sensorimotor neuropathy, indicating the involvement of the brain and peripheral nerves. DIAGNOSES: Finally, a diagnosis of autoimmune GFAP astrocytopathy was confirmed due to the presence of GFAP-immunoglobulinG in the patient's CSF. INTERVENTIONS: The patient was treated with one course of intravenous immunoglobulin therapy, then followed with intravenous methylprednisolone (1.0 g/d for 3 days) and oral prednisolone. OUTCOMES: At 1 week after intravenous immunoglobulin therapy, his level of consciousness improved. However, flaccid paralysis persisted without substantial improvement. CONCLUSION: In conclusion, the provision of an accurate early diagnosis and appropriate treatment are crucial for improving the prognosis of patients with autoimmune GFAP astrocytopathy. Further, this case highlights the importance of recognizing the role of peripheral nerve involvement in GFAP autoimmunity.

Mild Microglial Responses in the Cortex and Perivascular Macrophage Infiltration in Subcortical White Matter in Dogs with Age-Related Dementia Modelling Prodromal Alzheimer's Disease.

BACKGROUND: Microglia contribute to Alzheimer's disease (AD) pathogenesis by clearing amyloid-ß (Aß) and driving neuroinflammation. Domestic dogs with age-related dementia (canine cognitive dysfunction (CCD)) develop cerebral amyloidosis like humans developing AD, and studying such dogs can provide novel information about microglial response in prodromal AD. OBJECTIVE: The aim was to investigate the microglial response in the cortical grey and the subcortical white matter in dogs with CCD versus age-matched cognitively normal dogs. METHODS: Brains from aged dogs with CCD and age-matched controls without dementia were studied. Cases were defined by dementia rating score. Brain sections were stained for Aß, thioflavin S, hyperphosphorylated tau, and the microglial-macrophage ionized calcium binding adaptor molecule 1 (Iba1). Results were correlated to dementia rating score and tissue levels of Aß. RESULTS: Microglial numbers were higher in the Aß plaque-loaded deep cortical layers in CCD versus control dogs, while the coverage by microglial processes were comparable. Aß plaques were of the diffuse type and without microglial aggregation. However, a correlation was found between the %Iba1 area and insoluble Aß 42 and N-terminal pyroglutamate modified Aß(N3pE)-42. The %Iba1 area was higher in white matter, showing phosphorylation of S396 tau, versus grey matter. Perivascular macrophage infiltrates were abundant in the white matter particularly in CDD dogs. CONCLUSION: The results from this study of the microglial-macrophage response in dogs with CCD are suggestive of relatively mild microglial responses in the Aß plaque-loaded deep cortical layers and perivascular macrophage infiltrates in the subcortical white matter, in prodromal AD.

Treg cell-derived osteopontin promotes microglia-mediated white matter repair after ischemic stroke.

The precise mechanisms underlying the beneficial effects of regulatory T (Treg) cells on long-term tissue repair remain elusive. Here, using single-cell RNA sequencing and flow cytometry, we found that Treg cells infiltrated the brain 1 to 5 weeks after experimental stroke in mice. Selective depletion of Treg cells diminished oligodendrogenesis, white matter repair, and functional recovery after stroke. Transcriptomic analyses revealed potent immunomodulatory effects of brain-infiltrating Treg cells on other immune cells, including monocyte-lineage cells. Microglia depletion, but not T cell lymphopenia, mitigated the beneficial effects of transferred Treg cells on white matter regeneration. Mechanistically, Treg cell-derived osteopontin acted through integrin receptors on microglia to enhance microglial reparative activity, consequently promoting oligodendrogenesis and white matter repair. Increasing Treg cell numbers by delivering IL-2:IL-2 antibody complexes after stroke improved white matter integrity and rescued neurological functions over the long term. These findings reveal Treg cells as a neurorestorative target for stroke recovery.

T Cells Actively Infiltrate the White Matter of the Aging Monkey Brain in Relation to Increased Microglial Reactivity and Cognitive Decline.

Normal aging is characterized by declines in processing speed, learning, memory, and executive function even in the absence of neurodegenerative diseases such as Alzheimer's Disease (AD). In normal aging monkeys and humans, neuronal loss does not account for cognitive impairment. Instead, loss of white matter volume and an accumulation of myelin sheath pathology begins in middle age and is associated with cognitive decline. It is unknown what causes this myelin pathology, but it likely involves increased neuroinflammation in white matter and failures in oligodendrocyte function (maturation and repair). In frontal white matter tracts vulnerable to myelin damage, microglia become chronically reactive and secrete harmful pro-inflammatory cytokines. Despite being in a phagocytic state, these microglia are ineffective at phagocytosing accruing myelin debris, which directly inhibits myelin sheath repair. Here, we asked whether reported age-related increases in pro-inflammatory markers were accompanied by an adaptive immune response involving T cells. We quantified T cells with immunohistochemistry in the brains of 34 cognitively characterized monkeys and found an age-related increase in perivascular T cells that surround CNS vasculature. We found a surprising age-related increase in T cells that infiltrate the white matter parenchyma. In the cingulum bundle the percentage of these parenchymal T cells increased with age relative to those in the perivascular space. In contrast, infiltrating T cells were rarely found in surrounding gray matter regions. We assessed whether T cell infiltration correlated with fibrinogen extravasation from the vasculature as a measure of BBB leakiness and found no correlation, suggesting that T cell infiltration is not a result of passive extravasation. Importantly, the density of T cells in the cingulum bundle correlated with microglial reactivity and with cognitive impairment. This is the first demonstration that T cell infiltration of white matter is associated with cognitive decline in the normal aging monkey.

Structural and Clinical Correlates of a Periventricular Gradient of Neuroinflammation in Multiple Sclerosis.

OBJECTIVES: To explore in vivo innate immune cell activation as a function of the distance from ventricular CSF in patients with multiple sclerosis (MS) using [18F]-DPA714 PET and to investigate its relationship with periventricular microstructural damage, evaluated by magnetization transfer ratio (MTR), and with trajectories of disability worsening. METHODS: Thirty-seven patients with MS and 19 healthy controls underwent MRI and [18F]-DPA714 TSPO dynamic PET, from which individual maps of voxels characterized by innate immune cell activation (DPA+) were generated. White matter (WM) was divided in 3-mm-thick concentric rings radiating from the ventricular surface toward the cortex, and the percentage of DPA+ voxels and mean MTR were extracted from each ring. Two-year trajectories of disability worsening were collected to identify patients with and without recent disability worsening. RESULTS: The percentage of DPA+ voxels was higher in patients compared to controls in the periventricular WM (p = 6.10e-6) and declined with increasing distance from ventricular surface, with a steeper gradient in patients compared to controls (p = 0.001). This gradient was found in both periventricular lesions and normal-appearing WM. In the total WM, it correlated with a gradient of microstructural tissue damage measured by MTR (r s = -0.65, p = 1.0e-3). Compared to clinically stable patients, patients with disability worsening were characterized by a higher percentage of DPA+ voxels in the periventricular normal-appearing WM (p = 0.025). CONCLUSIONS: Our results demonstrate that in MS the innate immune cell activation predominates in periventricular regions and is associated with microstructural damage and disability worsening. This could result from the diffusion of proinflammatory CSF-derived factors into surrounding tissues.

QSM is an imaging biomarker for chronic glial activation in multiple sclerosis lesions.

BACKGROUND: Inflammation in chronic active lesions occurs behind a closed blood-brain barrier and cannot be detected with MRI. Activated microglia are highly enriched for iron and can be visualized with quantitative susceptibility mapping (QSM), an MRI technique used to delineate iron. OBJECTIVE: To characterize the histopathological correlates of different QSM hyperintensity patterns in MS lesions. METHODS: MS brain slabs were imaged with MRI and QSM, and processed for histology. Immunolabeled cells were quantified in the lesion rim, center, and adjacent normal-appearing white matter (NAWM). Iron+ myeloid cell densities at the rims were correlated with susceptibilities. Human-induced pluripotent stem cell (iPSC)-derived microglia were used to determine the effect of iron on the production of reactive oxygen species (ROS) and pro-inflammatory cytokines. RESULTS: QSM hyperintensity at the lesion perimeter correlated with activated iron+ myeloid cells in the rim and NAWM. Lesions with high punctate or homogenous QSM signal contained no or minimally activated iron- myeloid cells. In vitro, iron accumulation was highest in M1-polarized human iPSC-derived microglia, but it did not enhance ROS or cytokine production. CONCLUSION: A high QSM signal outlining the lesion rim but not punctate signal in the center is a biomarker for chronic inflammation in white matter lesions.

White matter demyelination predates axonal injury after ischemic stroke in cynomolgus monkeys.

Unraveling the pathology of stroke is a prerequisite for designing therapeutic strategies. It was reported that myelin injury exceeded axonal loss in the peri-infarct region of rodent white matter stroke. An in-depth investigation of the post-stroke white matter damage in higher-order species might innovate stroke intervention. In this study, adult male cynomolgus monkeys received surgical middle cerebral artery occlusion (MCAO), and serial magnetic resonance scans to non-invasively assess brain damage. Spontaneous movements were recorded to evaluate post-stroke behavior. The axon and myelin loss, as well as immune cell infiltration were examined using immunohistochemistry. Magnetic resonance imaging revealed cerebral infarcts and white matter injury after MCAO in monkeys, which were confirmed by neurological deficits. Immunostaining of white matter fibers showed substantial demyelination whilst retention of axons in the infarcts 8 days post MCAO, while a progressive loss of myelin and axons was observed after one month. Gliosis, microglia activation, and leukocyte infiltration were identified in the lesions. These results demonstrate that demyelination predates axonal injury in non-human primate ischemic stroke, which provides a time window for stroke intervention focusing on prevention of progressive axonal loss through myelin regeneration.

The immune-inflammatory response of oligodendrocytes in a murine model of preterm white matter injury: the role of TLR3 activation.

A leading cause of preterm birth is the exposure to systemic inflammation (maternal/fetal infection), which leads to neuroinflammation and white matter injury (WMI). A wide range of cytokines and chemokines are expressed and upregulated in oligodendrocytes (OLs) in response to inflammation and numerous reports show that OLs express several receptors for immune related molecules, which enable them to sense inflammation and to react. However, the role of OL immune response in WMI is unclear. Here, we focus our study on toll-like receptor-3 (TLR3) that is activated by double-strand RNA (dsRNA) and promotes neuroinflammation. Despite its importance, its expression and role in OLs remain unclear. We used an in vivo mouse model, which mimics inflammation-mediated WMI of preterm born infants consisting of intraperitoneal injection of IL-1ß from P1 to P5. In the IL-1ß-treated animals, we observed the upregulation of Tlr3, IL-1ß, IFN-ß, Ccl2, and Cxcl10 in both PDGFRα+ and O4+ sorted cells. This upregulation was higher in O4+ immature OLs (immOLs) as compared to PDGFRα+ OL precursor cells (OPCs), suggesting a different sensitivity to neuroinflammation. These observations were confirmed in OL primary cultures: cells treated with TLR3 agonist Poly(I:C) during differentiation showed a stronger upregulation of Ccl2 and Cxcl10 compared to cells treated during proliferation and led to decreased expression of myelin genes. Finally, OLs were able to modulate microglia phenotype and function depending on their maturation state as assessed by qPCR using validated markers for immunomodulatory, proinflammatory, and anti-inflammatory phenotypes and by phagocytosis and morphological analysis. These results show that during inflammation the response of OLs can play an autonomous role in blocking their own differentiation: in addition, the immune activation of OLs may play an important role in shaping the response of microglia during inflammation.

White matter lesions in multiple sclerosis are enriched for CD20dim CD8+ tissue-resident memory T cells.

Brain CD8+ CD69+ tissue-resident memory T (TRM ) cells comprise a CD20dim subset, which is proportionally larger in CD103-negative TRM cells. In multiple sclerosis (MS) lesions, CD20dim TRM -cell proportions are increased. CD20-expression is associated with higher levels of CXCR6, Ki-67, and granzyme B, supporting CD20dim TRM cells as a relevant subset in MS.

Neuroinflammation in the normal-appearing white matter (NAWM) of the multiple sclerosis brain causes abnormalities at the nodes of Ranvier.

Changes to the structure of nodes of Ranvier in the normal-appearing white matter (NAWM) of multiple sclerosis (MS) brains are associated with chronic inflammation. We show that the paranodal domains in MS NAWM are longer on average than control, with Kv1.2 channels dislocated into the paranode. These pathological features are reproduced in a model of chronic meningeal inflammation generated by the injection of lentiviral vectors for the lymphotoxin-α (LTα) and interferon-γ (IFNγ) genes. We show that tumour necrosis factor (TNF), IFNγ, and glutamate can provoke paranodal elongation in cerebellar slice cultures, which could be reversed by an N-methyl-D-aspartate (NMDA) receptor blocker. When these changes were inserted into a computational model to simulate axonal conduction, a rapid decrease in velocity was observed, reaching conduction failure in small diameter axons. We suggest that glial cells activated by pro-inflammatory cytokines can produce high levels of glutamate, which triggers paranodal pathology, contributing to axonal damage and conduction deficits.

Brain-homing CD4+ T cells display glucocorticoid-resistant features in MS.

OBJECTIVE: To study whether glucocorticoid (GC) resistance delineates disease-relevant T helper (Th) subsets that home to the CNS of patients with early MS. METHODS: The expression of key determinants of GC sensitivity, multidrug resistance protein 1 (MDR1/ABCB1) and glucocorticoid receptor (GR/NR3C1), was investigated in proinflammatory Th subsets and compared between natalizumab-treated patients with MS and healthy individuals. Blood, CSF, and brain compartments from patients with MS were assessed for the recruitment of GC-resistant Th subsets using fluorescence-activated cell sorting (FACS), quantitative polymerase chain reaction (qPCR), immunohistochemistry, and immunofluorescence. RESULTS: An MS-associated Th subset termed Th17.1 showed a distinct GC-resistant phenotype as reflected by high MDR1 and low GR expression. This expression ratio was further elevated in Th17.1 cells that accumulated in the blood of patients with MS treated with natalizumab, a drug that prevents their entry into the CNS. Proinflammatory markers C-C chemokine receptor 6, IL-23R, IFN-γ, and GM-CSF were increased in MDR1-expressing Th17.1 cells. This subset predominated the CSF of patients with early MS, which was not seen in the paired blood or in the CSF from patients with other inflammatory and noninflammatory neurologic disorders. The potential of MDR1-expressing Th17.1 cells to infiltrate brain tissue was confirmed by their presence in MS white matter lesions. CONCLUSION: This study reveals that GC resistance coincides with preferential CNS recruitment of pathogenic Th17.1 cells, which may hamper the long-term efficacy of GCs in early MS.

Progressive Multiple Sclerosis Transcriptome Deconvolution Indicates Increased M2 Macrophages in Inactive Lesions.

Accumulating evidence suggests M2 macrophages contribute to tissue reparation and limit inflammation in multiple sclerosis (MS). However, most studies have focused on murine models without substantial support through human MS observations. The present study aimed to quantify the relative abundances of M2 macrophages in different lesion types excised from human MS patients. CIBERSORTx, an established RNA deconvolution algorithm, was applied on bulk RNA-sequencing data developed from 98 lesions from 10 progressive MS patients and 5 neuropathological control donors. A validated gene signature matrix for 22 human hematopoietic cell subsets was used to infer the relative proportions of immune cells that were present in the original lesion. Deconvolution of the bulk gene expression data showed that inactive lesions contained significantly more M2 macrophages compared to normal white matter control samples. The findings suggest that M2 macrophages may play a role during lesion inactivity in MS.

Perivascular tissue resident memory T cells as therapeutic target in multiple sclerosis.

INTRODUCTION: Multiple sclerosis (MS) is characterized by inflammatory attacks of infiltrating leukocytes at onset but evolves into a smoldering, progressive disease within the central nervous system at its later stages. The authors discuss the contribution of white matter lesions to the pathology of advanced MS, thereby paying particular attention to the role of T cells. AREAS COVERED: Diagnostic biopsy and autopsy studies of white matter lesions in early MS show different pathological patterns of demyelination and leukocyte infiltration. Brain autopsies from advanced MS display substantial inflammation without distinct patterns and suggest a role for perivascular CD8+ tissue-resident memory T (TRM) cells in active and mixed active/inactive MS white matter lesions. When compared to control and normal-appearing white matter, these lesions are enriched for parenchymal CD8+ T cells. In the perivascular space, cuffs containing CD8+ TRM cells are observed also in progressive MS, and could be sites of local reactivation. EXPERT OPINION: Recent findings point toward the perivascular space as an immunological hotspot, which could be targeted in order to suppress a contribution of TRM cells to ongoing white matter lesion activity in advanced progressive MS. The authors discuss approaches, which may be explored to suppress TRM-cell reactivation in the perivascular space.

Tissue-resident memory T cells invade the brain parenchyma in multiple sclerosis white matter lesions.

Multiple sclerosis is a chronic inflammatory, demyelinating disease, although it has been suggested that in the progressive late phase, inflammatory lesion activity declines. We recently showed in the Netherlands Brain Bank multiple sclerosis-autopsy cohort considerable ongoing inflammatory lesion activity also at the end stage of the disease, based on microglia/macrophage activity. We have now studied the role of T cells in this ongoing inflammatory lesion activity in chronic multiple sclerosis autopsy cases. We quantified T cells and perivascular T-cell cuffing at a standardized location in the medulla oblongata in 146 multiple sclerosis, 20 neurodegenerative control and 20 non-neurological control brain donors. In addition, we quantified CD3+, CD4+, and CD8+ T cells in 140 subcortical white matter lesions. The location of CD8+ T cells in either the perivascular space or the brain parenchyma was determined using CD8/laminin staining and confocal imaging. Finally, we analysed CD8+ T cells, isolated from fresh autopsy tissues from subcortical multiple sclerosis white matter lesions (n = 8), multiple sclerosis normal-appearing white matter (n = 7), and control white matter (n = 10), by flow cytometry. In normal-appearing white matter, the number of T cells was increased compared to control white matter. In active and mixed active/inactive lesions, the number of T cells was further augmented compared to normal-appearing white matter. Active and mixed active/inactive lesions were enriched for both CD4+ and CD8+ T cells, the latter being more abundant in all lesion types. Perivascular clustering of T cells in the medulla oblongata was only found in cases with a progressive disease course and correlated with a higher percentage of mixed active/inactive lesions and a higher lesion load compared to cases without perivascular clusters in the medulla oblongata. In all white matter samples, CD8+ T cells were located mostly in the perivascular space, whereas in mixed active/inactive lesions, 16.3% of the CD8+ T cells were encountered in the brain parenchyma. CD8+ T cells from mixed active/inactive lesions showed a tissue-resident memory phenotype with expression of CD69, CD103, CD44, CD49a, and PD-1 and absence of S1P1. They upregulated markers for homing (CXCR6), reactivation (Ki-67), and cytotoxicity (GPR56), yet lacked the cytolytic enzyme granzyme B. These data show that in chronic progressive multiple sclerosis cases, inflammatory lesion activity and demyelinated lesion load is associated with an increased number of T cells clustering in the perivascular space. Inflammatory active multiple sclerosis lesions are populated by CD8+ tissue-resident memory T cells, which show signs of reactivation and infiltration of the brain parenchyma.

Correlation of microglial activation with white matter changes in dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) is characterized by alpha-synuclein protein deposition with variable degree of concurrent Alzheimer's pathology. Neuroinflammation is also increasingly recognized as a significant contributor to degeneration. We aimed to examine the relationship between microglial activation as measured with [11C]-PK11195 brain PET, MR diffusion tensor imaging (DTI) and grey matter atrophy in DLB. Nineteen clinically probable DLB and 20 similarly aged controls underwent 3T structural MRI (T1-weighted) and diffusion-weighted imaging. Eighteen DLB subjects also underwent [11C]-PK11195 PET imaging and 15 had [11C]-Pittsburgh compound B amyloid PET, resulting in 9/15 being amyloid-positive. We used Computational Anatomy Toolbox (CAT12) for volume-based morphometry (VBM) and Tract-Based Spatial Statistics (TBSS) for DTI to assess group comparisons between DLB and controls and to identify associations of [11C]-PK11195 binding with grey/white matter changes and cognitive score in DLB patients. VBM analyses showed that DLB had extensive reduction of grey matter volume in superior frontal, temporal, parietal and occipital cortices (family-wise error (FWE)-corrected p < 0.05). TBSS showed widespread changes in DLB for all DTI parameters (reduced fractional anisotropy, increased diffusivity), involving the corpus callosum, corona radiata and superior longitudinal fasciculus (FWE-corrected p < 0.05). Higher [11C]-PK11195 binding in parietal cortices correlated with widespread lower mean and radial diffusivity in DLB patients (FWE-corrected p < 0.05). Furthermore, preserved cognition in DLB (higher Addenbrookes Cognitive Evaluation revised score) also correlated with higher [11C]-PK11195 binding in frontal, temporal, and occipital lobes. However, microglial activation was not significantly associated with grey matter changes. Our study suggests that increased microglial activation is associated with a relative preservation of white matter and cognition in DLB, positioning neuroinflammation as a potential early marker of DLB etio-pathogenesis.

An IL-18-centered inflammatory network as a biomarker for cerebral white matter injury.

Chronic systemic sterile inflammation is implicated in the pathogenesis of cerebrovascular disease and white matter injury. Non-invasive blood markers for risk stratification and dissection of inflammatory molecular substrates in vivo are lacking. We sought to identify whether an interconnected network of inflammatory biomarkers centered on IL-18 and all previously associated with white matter lesions could detect overt and antecedent white matter changes in two populations at risk for cerebral small vessel disease. In a cohort of 167 older adults (mean age: 76, SD 7.1, 83 females) that completed a cognitive battery, physical examination, and blood draw in parallel with MR imaging including DTI, we measured cerebral white matter hyperintensities (WMH) and free water (FW). Concurrently, serum levels of a biologic network of inflammation molecules including MPO, GDF-15, RAGE, ST2, IL-18, and MCP-1 were measured. The ability of a log-transformed population mean-adjusted inflammatory composite score (ICS) to associate with MR variables was demonstrated in an age and total intracranial volume adjusted model. In this cohort, ICS was significantly associated with WMH (ß = 0.222, p = 0.013), FW (ß = 0.3, p = 0.01), and with the number of vascular risk factor diagnoses (r = 0.36, p<0.001). In a second cohort of 131 subjects presenting for the evaluation of acute neurologic deficits concerning for stroke, we used serum levels of 11 inflammatory biomarkers in an unbiased principal component analysis which identified a single factor significantly associated with WMH. This single factor was strongly correlated with the six component ICS identified in the first cohort and was associated with WMH in a generalized linear regression model adjusted for age and gender (p = 0.027) but not acute stroke. A network of inflammatory molecules driven by IL-18 is associated with overt and antecedent white matter injury resulting from cerebrovascular disease and may be a promising peripheral biomarker for vascular white matter injury.

Evidence of diffuse cerebellar neuroinflammation in multiple sclerosis by 11C-PBR28 MR-PET.

BACKGROUND: Activated microglia, which can be detected in vivo by 11C-PBR28 positron emission tomography (PET), represent a main component of MS pathology in the brain. Their role in the cerebellum is still unexplored, although cerebellar involvement in MS is frequent and accounts for disability progression. OBJECTIVES: We aimed at characterizing cerebellar neuroinflammation in MS patients compared to healthy subjects by combining 11C-PBR28 MRI-Positron Emission Tomography (MR-PET) with 7 Tesla (T) MRI and assessing its relationship with brain neuroinflammation and clinical outcome measures. METHODS: Twenty-eight MS patients and 16 healthy controls underwent 11C-PBR28 MR-PET to measure microglia activation in normal appearing cerebellum and lesions segmented from 7 T scans. Patients were evaluated using the Expanded Disability Status Scale and Symbol Digit Modalities Test. 11C-PBR28 binding was assessed in regions of interest using 60-90 minutes standardized uptake values normalized by a pseudo-reference region in the brain normal appearing white matter. Multilinear regression was used to compare tracer uptake in MS and healthy controls and assess correlations with clinical scores. RESULTS: In all cerebellar regions examined, MS patients showed abnormally increased tracer uptake, which correlated with cognitive and neurological disability. CONCLUSION: Neuroinflammation is widespread in the cerebellum of patients with MS and related to neurological disability and cognitive impairment.