Astrocytes and microglia differentially regulate trafficking of lymphocyte subsets across brain endothelial cells

The Blood-Brain Barrier: Composition, Properties, and Roles in Brain Health

Blood vessels are critical to deliver oxygen and nutrients to tissues and organs throughout the body. The blood vessels that vascularize the central nervous system (CNS) possess unique properties, termed the blood-brain barrier (BBB), which allow these vessels to tightly regulate the movement of ions, molecules, and cells between the blood and the brain. This precise control of CNS homeostasis allows for proper neuronal function and protects the neural tissue from toxins and pathogens, and alterations of this barrier are important components of the pathogenesis and progression of various neurological diseases. The physiological barrier is coordinated by a series of physical, transport, and metabolic properties possessed by the brain endothelial cells (ECs) that form the walls of the blood vessels. These properties are regulated by interactions between different vascular, perivascular, immune, and neural cells. Understanding how these cell populations interact to regulate barrier properties is essential for understanding how the brain functions in both health and disease contexts.

Chronic Inflammation Offers Hints About Viable Therapeutic Targets for Preeclampsia and Potentially Related Offspring Sequelae

The combination of hypertension with systemic inflammation during pregnancy is a hallmark of preeclampsia, but both processes also convey dynamic information about its antecedents and correlates (e.g., fetal growth restriction) and potentially related offspring sequelae. Causal inferences are further complicated by the increasingly frequent overlap of preeclampsia, fetal growth restriction, and multiple indicators of acute and chronic inflammation, with decreased gestational length and its correlates (e.g., social vulnerability). This complexity prompted our group to summarize information from mechanistic studies, integrated with key clinical evidence, to discuss the possibility that sustained or intermittent systemic inflammation-related phenomena offer hints about viable therapeutic targets, not only for the prevention of preeclampsia, but also the neurobehavioral and other developmental deficits that appear to be overrepresented in surviving offspring. Importantly, we feel that carefully designed hypothesis-driven observational studies are necessary if we are to translate the mechanistic evidence into child health benefits, namely because multiple pregnancy disorders might contribute to heightened risks of neuroinflammation, arrested brain development, or dysconnectivity in survivors who exhibit developmental problems later in life.

Influence of Tau on Neurotoxicity and Cerebral Vasculature Impairment Associated with Alzheimer's Disease

Alzheimer's disease is a fatal chronic neurodegenerative condition marked by a gradual decline in cognitive abilities and impaired vascular function within the central nervous system. This affliction initiates its insidious progression with the accumulation of two aberrant protein entities including Aβ plaques and neurofibrillary tangles. These chronic elements target distinct brain regions, steadily erasing the functionality of the hippocampus and triggering the erosion of memory and neuronal integrity. Several assumptions are anticipated for AD as genetic alterations, the occurrence of Aβ plaques, altered processing of amyloid precursor protein, mitochondrial damage, and discrepancy of neurotropic factors. In addition to Aβ oligomers, the deposition of tau hyper-phosphorylates also plays an indispensable part in AD etiology. The brain comprises a complex network of capillaries that is crucial for maintaining proper function. Tau is expressed in cerebral blood vessels, where it helps to regulate blood flow and sustain the blood-brain barrier's integrity. In AD, tau pathology can disrupt cerebral blood supply and deteriorate the BBB, leading to neuronal neurodegeneration. Neuroinflammation, deficits in the microvasculature and endothelial functions, and Aβ deposition are characteristically detected in the initial phases of AD. These variations trigger neuronal malfunction and cognitive impairment. Intracellular tau accumulation in microglia and astrocytes triggers deleterious effects on the integrity of endothelium and cerebral blood supply resulting in further advancement of the ailment and cerebral instability. In this review, we will discuss the impact of tau on neurovascular impairment, mitochondrial dysfunction, oxidative stress, and the role of hyperphosphorylated tau in neuron excitotoxicity and inflammation.

Chronic Stress-Induced Neuroinflammation: Relevance of Rodent Models to Human Disease

The brain is the central organ of adaptation to stress because it perceives and determines threats that induce behavioral, physiological, and molecular responses. In humans, chronic stress manifests as an enduring consistent feeling of pressure and being overwhelmed for an extended duration. This can result in a persistent proinflammatory response in the peripheral and central nervous system (CNS), resulting in cellular, physiological, and behavioral effects. Compounding stressors may increase the risk of chronic-stress-induced inflammation, which can yield serious health consequences, including mental health disorders. This review summarizes the current knowledge surrounding the neuroinflammatory response in rodent models of chronic stress-a relationship that is continually being defined. Many studies investigating the effects of chronic stress on neuroinflammation in rodent models have identified significant changes in inflammatory modulators, including nuclear factor-κB (NF-κB) and toll-like receptors (TLRs), and cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and IL-6. This suggests that these are key inflammatory factors in the chronic stress response, which may contribute to the establishment of anxiety and depression-like symptoms. The behavioral and neurological effects of modulating inflammatory factors through gene knockdown (KD) and knockout (KO), and conventional and alternative medicine approaches, are discussed.

Astrocyte Involvement in Blood-Brain Barrier Function: A Critical Update Highlighting Novel, Complex, Neurovascular Interactions

Neurological disorders have been linked to a defective blood-brain barrier (BBB), with dysfunctions triggered by stage-specific disease mechanisms, some of these being generated through interactions in the neurovascular unit (NVU). Advanced knowledge of molecular and signaling mechanisms in the NVU and the emergence of improved experimental models allow BBB permeability prediction and the development of new brain-targeted therapies. As NVU constituents, astrocytes are the most numerous glial cells, characterized by a heterogeneity that occurs as a result of developmental and context-based gene expression profiles and the differential expression of non-coding ribonucleic acids (RNAs). Due to their heterogeneity and dynamic responses to different signals, astrocytes may have a beneficial or detrimental role in the BBB's barrier function, with deep effects on the pathophysiology of (and on the progression of) central nervous system diseases. The implication of astrocytic-derived extracellular vesicles in pathological mechanisms, due to their ability to pass the BBB, must also be considered. The molecular mechanisms of astrocytes' interaction with endothelial cells at the BBB level are considered promising therapeutic targets in different neurological conditions. Nevertheless, a personalized and well-founded approach must be addressed, due to the temporal and spatial heterogeneity of reactive astrogliosis states during disease.

The Rare Marine Bioactive Compounds in Neurological Disorders and Diseases: Is the Blood-Brain Barrier an Obstacle or a Target?

The blood-brain barrier (BBB) is a dynamic barrier separating neurocytes and brain tissues from blood that is extremely sealed and strictly regulated by transporters such as aquaporin-4 (AQP-4), glucose transporter (GLUT), and specialized tight junctional complexes (TJCs) including tight junctions (TJs), adherens junctions (AJs), and Zonulae occludens (ZOs). With specifically selective transcellular and paracellular permeability, the BBB maintains a homeostatic microenvironment to protect the central nervous system (CNS). In recent years, increasing attention has been paied to the importance of BBB disruption and dysfunction in the pathology of neurological disorders and diseases, such as Alzheimer's diseases (AD), Parkinson diseases (PD), stroke and cerebral edema. However, the further research on how the integral structure and function of BBB are altered under the physiological or pathological conditions is still needed. Focusing on the ultrastructural features of the BBB and combining the latest research on associated proteins and transporters, physiological regulation and pathological change of the BBB were elucidated. By summarizing the protective effects of known bioactive compounds derived from marine life on the BBB, this review aims to highlight the BBB as a key to the treatment of several major neurological diseases instead of a normally described obstacle to drug absorption and transport. Overall, the BBB's morphological characteristics and physiological function and their regulation provide the theoretical basis for the study on the BBB and inspire the diagnosis of and therapy for neurological diseases.

Nerve growth factor receptor (Ngfr) induces neurogenic plasticity by suppressing reactive astroglial Lcn2/Slc22a17 signaling in Alzheimer's disease

Neurogenesis, crucial for brain resilience, is reduced in Alzheimer's disease (AD) that induces astroglial reactivity at the expense of the pro-neurogenic potential, and restoring neurogenesis could counteract neurodegenerative pathology. However, the molecular mechanisms promoting pro-neurogenic astroglial fate despite AD pathology are unknown. In this study, we used APP/PS1dE9 mouse model and induced Nerve growth factor receptor (Ngfr) expression in the hippocampus. Ngfr, which promotes neurogenic fate of astroglia during the amyloid pathology-induced neuroregeneration in zebrafish brain, stimulated proliferative and neurogenic outcomes. Histological analyses of the changes in proliferation and neurogenesis, single-cell transcriptomics, spatial proteomics, and functional knockdown studies showed that the induced expression of Ngfr reduced the reactive astrocyte marker Lipocalin-2 (Lcn2), which we found was sufficient to reduce neurogenesis in astroglia. Anti-neurogenic effects of Lcn2 was mediated by Slc22a17, blockage of which recapitulated the pro-neurogenicity by Ngfr. Long-term Ngfr expression reduced amyloid plaques and Tau phosphorylation. Postmortem human AD hippocampi and 3D human astroglial cultures showed elevated LCN2 levels correlate with reactive gliosis and reduced neurogenesis. Comparing transcriptional changes in mouse, zebrafish, and human AD brains for cell intrinsic differential gene expression and weighted gene co-expression networks revealed common altered downstream effectors of NGFR signaling, such as PFKP, which can enhance proliferation and neurogenesis in vitro when blocked. Our study suggests that the reactive non-neurogenic astroglia in AD can be coaxed to a pro-neurogenic fate and AD pathology can be alleviated with Ngfr. We suggest that enhancing pro-neurogenic astroglial fate may have therapeutic ramifications in AD.

Blood brain barrier and inflammation in depression

The blood brain barrier (BBB) is a vital structure to protect the brain, tightly filtering the passage of nutrients and molecules from the blood to the brain. This is critical for maintaining the proper functioning of the brain, and any disruption in the BBB has detrimental consequences often leading to diseases. It is not clear whether disruption of the BBB occurs first in depression or is the consequence of the disease, however disruption of the BBB has been observed in depressed patients and evidence points to the role of important culprits in depression, stress and inflammation in disrupting the integrity of the BBB. The mechanisms whereby stress, and inflammation affect the BBB remain to be fully understood. Yet, the role of cytokines in regulating tight junction protein expression seems crucial. Altogether, the findings in depression suggest that acting at the BBB level might provide therapeutic benefit in depression.

Central nervous system commitment in Chagas disease

The involvement of the central nervous system (CNS) during human acute and chronic Chagas disease (CD) has been largely reported. Meningoencephalitis is a frequent finding during the acute infection, while during chronic phase the CNS involvement is often accompanied by behavioral and cognitive impairments. In the same vein, several studies have shown that rodents infected with Trypanosoma cruzi (T. cruzi) display behavior abnormalities, accompanied by brain inflammation, in situ production of pro-inflammatory cytokines and parasitism in diverse cerebral areas, with involvement of microglia, macrophages, astrocytes, and neurons. However, the mechanisms used by the parasite to reach the brain remain now largely unknown. Herein we discuss the evidence unravelling the CNS involvement and complexity of neuroimmune interactions that take place in acute and chronic CD. Also, we provide some clues to hypothesize brain infections routes in human and experimental acute CD following oral infection by T. cruzi, an infection route that became a major CD related public health issue in Brazil.

Reactive astrocytes transduce inflammation in a blood-brain barrier model through a TNF-STAT3 signaling axis and secretion of alpha 1-antichymotrypsin

Astrocytes are critical components of the neurovascular unit that support blood-brain barrier (BBB) function. Pathological transformation of astrocytes to reactive states can be protective or harmful to BBB function. Here, using a human induced pluripotent stem cell (iPSC)-derived BBB co-culture model, we show that tumor necrosis factor (TNF) transitions astrocytes to an inflammatory reactive state that causes BBB dysfunction through activation of STAT3 and increased expression of SERPINA3, which encodes alpha 1-antichymotrypsin (α1ACT). To contextualize these findings, we correlated astrocytic STAT3 activation to vascular inflammation in postmortem human tissue. Further, in murine brain organotypic cultures, astrocyte-specific silencing of Serpina3n reduced vascular inflammation after TNF challenge. Last, treatment with recombinant Serpina3n in both ex vivo explant cultures and in vivo was sufficient to induce BBB dysfunction-related molecular changes. Overall, our results define the TNF-STAT3-α1ACT signaling axis as a driver of an inflammatory reactive astrocyte signature that contributes to BBB dysfunction.

Critical Role of Neuronal Vps35 in Blood Vessel Branching and Maturation in Developing Mouse Brain

Vps35 (vacuolar protein sorting 35), a key component of retromer, plays a crucial role in selective retrieval of transmembrane proteins from endosomes to trans-Golgi networks. Dysfunctional Vps35/retromer is a risk factor for the development of neurodegenerative diseases. Vps35 is highly expressed in developing pyramidal neurons, both in the mouse neocortex and hippocampus, Although embryonic neuronal Vps35’s function in promoting neuronal terminal differentiation and survival is evident, it remains unclear whether and how neuronal Vps35 communicates with other types of brain cells, such as blood vessels (BVs), which are essential for supplying nutrients to neurons. Dysfunctional BVs contribute to the pathogenesis of various neurodegenerative disorders. Here, we provide evidence for embryonic neuronal Vps35 as critical for BV branching and maturation in the developing mouse brain. Selectively knocking out (KO) Vps35 in mouse embryonic, not postnatal, neurons results in reductions in BV branching and density, arteriole diameter, and BV-associated pericytes and microglia but an increase in BV-associated reactive astrocytes. Deletion of microglia by PLX3397 enhances these BV deficits in mutant mice. These results reveal the function of neuronal Vps35 in neurovascular coupling in the developing mouse brain and implicate BV-associated microglia as underlying this event.

FMNL2 regulates gliovascular interactions and is associated with vascular risk factors and cerebrovascular pathology in Alzheimer's disease

Alzheimer's disease (AD) has been associated with cardiovascular and cerebrovascular risk factors (CVRFs) during middle age and later and is frequently accompanied by cerebrovascular pathology at death. An interaction between CVRFs and genetic variants might explain the pathogenesis. Genome-wide, gene by CVRF interaction analyses for AD, in 6568 patients and 8101 controls identified FMNL2 (p = 6.6 × 10-7). A significant increase in FMNL2 expression was observed in the brains of patients with brain infarcts and AD pathology and was associated with amyloid and phosphorylated tau deposition. FMNL2 was also prominent in astroglia in AD among those with cerebrovascular pathology. Amyloid toxicity in zebrafish increased fmnl2a expression in astroglia with detachment of astroglial end feet from blood vessels. Knockdown of fmnl2a prevented gliovascular remodeling, reduced microglial activity and enhanced amyloidosis. APP/PS1dE9 AD mice also displayed increased Fmnl2 expression and reduced the gliovascular contacts independent of the gliotic response. Based on this work, we propose that FMNL2 regulates pathology-dependent plasticity of the blood-brain-barrier by controlling gliovascular interactions and stimulating the clearance of extracellular aggregates. Therefore, in AD cerebrovascular risk factors promote cerebrovascular pathology which in turn, interacts with FMNL2 altering the normal astroglial-vascular mechanisms underlying the clearance of amyloid and tau increasing their deposition in brain.

Blood-Brain Barrier Dysfunction in CNS Disorders and Putative Therapeutic Targets: An Overview

The blood-brain barrier (BBB) is a fundamental component of the central nervous system (CNS). Its functional and structural integrity is vital to maintain the homeostasis of the brain microenvironment by controlling the passage of substances and regulating the trafficking of immune cells between the blood and the brain. The BBB is primarily composed of highly specialized microvascular endothelial cells. These cells’ special features and physiological properties are acquired and maintained through the concerted effort of hemodynamic and cellular cues from the surrounding environment. This complex multicellular system, comprising endothelial cells, astrocytes, pericytes, and neurons, is known as the neurovascular unit (NVU). The BBB strictly controls the transport of nutrients and metabolites into brain parenchyma through a tightly regulated transport system while limiting the access of potentially harmful substances via efflux transcytosis and metabolic mechanisms. Not surprisingly, a disruption of the BBB has been associated with the onset and/or progression of major neurological disorders. Although the association between disease and BBB disruption is clear, its nature is not always evident, specifically with regard to whether an impaired BBB function results from the pathological condition or whether the BBB damage is the primary pathogenic factor prodromal to the onset of the disease. In either case, repairing the barrier could be a viable option for treating and/or reducing the effects of CNS disorders. In this review, we describe the fundamental structure and function of the BBB in both healthy and altered/diseased conditions. Additionally, we provide an overview of the potential therapeutic targets that could be leveraged to restore the integrity of the BBB concomitant to the treatment of these brain disorders.

The Blood-Brain Barrier: Much More Than a Selective Access to the Brain

The blood-brain barrier is a dynamic structure, collectively referred to as the neurovascular unit. It is responsible for the exchange of blood, oxygen, ions, and other molecules between the peripheral circulation and the brain compartment. It is the main entrance to the central nervous system and as such critical for the maintenance of its homeostasis. Dysfunction of the blood-brain barrier is a characteristic of several neurovascular pathologies. Moreover, physiological changes, environmental factors, nutritional habits, and psychological stress can modulate the tightness of the barrier. In this contribution, we summarize our current understanding of structure and function of this important component of the brain. We also describe the neurological deficits associated with its damage. A special emphasis is placed in the effect of the exposure to xenobiotics and pollutants in the permeability of the barrier. Finally, current protective strategies as well as the culture models to study this fascinating structure are discussed.

Glial cells and adaptive immunity in frontotemporal dementia with tau pathology

Neuroinflammation is involved in the aetiology of many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease and motor neuron disease. Whether neuroinflammation also plays an important role in the pathophysiology of frontotemporal dementia is less well known. Frontotemporal dementia is a heterogeneous classification that covers many subtypes, with the main pathology known as frontotemporal lobar degeneration. The disease can be categorized with respect to the identity of the protein that causes the frontotemporal lobar degeneration in the brain. The most common subgroup describes diseases caused by frontotemporal lobar degeneration associated with tau aggregation, also known as primary tauopathies. Evidence suggests that neuroinflammation may play a role in primary tauopathies with genome-wide association studies finding enrichment of genetic variants associated with specific inflammation-related gene loci. These loci are related to both the innate immune system, including brain resident microglia, and the adaptive immune system through possible peripheral T-cell involvement. This review discusses the genetic evidence and relates it to findings in animal models expressing pathogenic tau as well as to post-mortem and PET studies in human disease. Across experimental paradigms, there seems to be a consensus regarding the involvement of innate immunity in primary tauopathies, with increased microglia and astrocyte density and/or activation, as well as increases in pro-inflammatory markers. Whilst it is less clear as to whether inflammation precedes tau aggregation or vice versa; there is strong evidence to support a microglial contribution to the propagation of hyperphosphorylated in tau frontotemporal lobar degeneration associated with tau aggregation. Experimental evidence-albeit limited-also corroborates genetic data pointing to the involvement of cellular adaptive immunity in primary tauopathies. However, it is still unclear whether brain recruitment of peripheral immune cells is an aberrant result of pathological changes or a physiological aspect of the neuroinflammatory response to the tau pathology.

Involvement of noncoding RNA in blood-brain barrier integrity in central nervous system disease

Given the important role of the blood-brain barrier (BBB) in the central nervous system (CNS), increasing studies have been carried out to determine how the structural and functional integrity of the BBB impacts the pathogenesis of CNS diseases such as stroke, traumatic brain injuries (TBIs), and gliomas. Emerging studies have revealed that noncoding RNAs (ncRNAs) help to maintain the integrity and permeability of the BBB, thereby mediating CNS homeostasis. This review summarizes recent studies that focus on the effects of ncRNAs on the BBB in CNS diseases, including regulating the biological processes of inflammation, necrosis, and apoptosis of cells, affecting the translational dysfunction of proteins and regulating tight junctions (TJs). A comprehensive and detailed understanding of the interaction between ncRNAs and the BBB will lay a solid foundation for the development of early diagnostic methods and effective treatments for CNS diseases.

Epigenetics in blood-brain barrier disruption

The vessels of the central nervous system (CNS) have unique barrier properties. The endothelial cells (ECs) which comprise the CNS vessels contribute to the barrier via strong tight junctions, specific transporters, and limited endocytosis which combine to protect the brain from toxins and maintains brain homeostasis. Blood-brain barrier (BBB) leakage is a serious secondary injury in various CNS disorders like stroke, brain tumors, and neurodegenerative disorders. Currently, there are no drugs or therapeutics available to treat specifically BBB damage after a brain injury. Growing knowledge in the field of epigenetics can enhance the understanding of gene level of the BBB and has great potential for the development of novel therapeutic strategies or targets to repair a disrupted BBB. In this brief review, we summarize the epigenetic mechanisms or regulators that have a protective or disruptive role for components of BBB, along with the promising approaches to regain the integrity of BBB.

Impact of Tau on Neurovascular Pathology in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most prevalent cause of dementia. The main cerebral histological hallmarks are represented by parenchymal insoluble deposits of amyloid beta (Aβ plaques) and neurofibrillary tangles (NFT), intracellular filamentous inclusions of tau, a microtubule-associated protein. It is well-established that cerebrovascular dysfunction is an early feature of AD pathology, but the detrimental mechanisms leading to blood vessel impairment and the associated neurovascular deregulation are not fully understood. In 90% of AD cases, Aβ deposition around the brain vasculature, known as cerebral amyloid angiopathy (CAA), alters blood brain barrier (BBB) essential functions. While the effects of vascular Aβ accumulation are better documented, the scientific community has only recently started to consider the impact of tau on neurovascular pathology in AD. Emerging compelling evidence points to transmission of neuronal tau to different brain cells, including astrocytes, as well as to the release of tau into brain interstitial fluids, which may lead to perivascular neurofibrillar tau accumulation and toxicity, affecting vessel architecture, cerebral blood flow (CBF), and vascular permeability. BBB integrity and functionality may therefore be impacted by pathological tau, consequentially accelerating the progression of the disease. Tau aggregates have also been shown to induce mitochondrial damage: it is known that tau impairs mitochondrial localization, distribution and dynamics, alters ATP and reactive oxygen species production, and compromises oxidative phosphorylation systems. In light of this previous knowledge, we postulate that tau can initiate neurovascular pathology in AD through mitochondrial dysregulation. In this review, we will explore the literature investigating tau pathology contribution to the malfunction of the brain vasculature and neurovascular unit, and its association with mitochondrial alterations and caspase activation, in cellular, animal, and human studies of AD and tauopathies.

The blood-brain barrier in health and disease: Important unanswered questions

The blood vessels vascularizing the central nervous system exhibit a series of distinct properties that tightly control the movement of ions, molecules, and cells between the blood and the parenchyma. This "blood-brain barrier" is initiated during angiogenesis via signals from the surrounding neural environment, and its integrity remains vital for homeostasis and neural protection throughout life. Blood-brain barrier dysfunction contributes to pathology in a range of neurological conditions including multiple sclerosis, stroke, and epilepsy, and has also been implicated in neurodegenerative diseases such as Alzheimer's disease. This review will discuss current knowledge and key unanswered questions regarding the blood-brain barrier in health and disease.

Genomic landscape of the immune microenvironments of brain metastases in breast cancer

Background

This study was intended to investigate the genomic landscape of the immune microenvironments of brain metastases in breast cancer.

Methods

Three gene expression profile datasets (GSE76714, GSE125989 and GSE43837) of breast cancer with brain metastases were downloaded from Gene Expression Omnibus (GEO) database. After differential expression analysis, the tumor immune microenvironment and immune cell infiltration were analyzed. Then immune-related genes were identified, followed by function analysis, transcription factor (TF)-miRNA–mRNA co-regulatory network analysis, and survival analysis of metastatic recurrence.

Results

The present results showed that the tumor immune microenvironment in brain metastases was immunosuppressed compared with primary caner. Compared with primary cancer samples, the infiltration ratio of plasma cells in brain metastases samples was significantly higher, while the infiltration ratio of macrophages M2 cells in brain metastases samples was significantly lower. Total 42 immune-related genes were identified, such as THY1 and NEU2. CD1B, THY1 and DOCK2 were found to be implicated in the metastatic recurrence of breast cancer.

Conclusions

Targeting macrophages or plasma cells may be new strategies for immunotherapy of breast cancer with brain metastases. THY1 and NEU2 may be potential therapeutic targets for breast cancer with brain metastases, and THY1, CD1B and DOCK2 may serve as potential prognostic markers for improvement of brain metastases survival.

Characterization of the immune microenvironment in brain metastases from different solid tumors

BACKGROUND

Brain metastases are one of the most common intracranial neoplasms. Increasing evidence have indicated that systemic immunotherapy may provide long-term benefits for brain metastases. Herein, we presented the results of an immune oncology panel RNA sequencing platform for patients with brain metastases from different primary sites.

METHODS

We investigated 25 samples of human brain metastases from lung cancer (n = 12), breast cancer (n = 6), and colorectal cancer (n = 7). Besides, 13 paired samples of adjacent noncancerous brain tissue (10 from patients with lung cancer and 3 from patients with breast cancer) were collected as controls. By comparing the brain metastases and paired samples of adjacent noncancerous brain tissue from 13 patients, we detected three upregulated and six downregulated genes, representing the malignant properties of cancer cells and increased immune infiltration in the microenvironment. Next, we profiled the immune-related genes in brain metastases from three primary cancer types.

RESULTS

A group of genes were significantly overexpressed in the microenvironment of brain metastases from lung cancer, covering the checkpoint pathways, lymphocyte infiltration, and TCR-coexpression. Especially, immune checkpoint molecules, PD-L1, PD-L2, and IDO1 were expressed at higher levels in brain metastases from lung cancer than those from the other two cancer types.

CONCLUSIONS

This study presents an immune landscape of brain metastases from different cancer types. With high RNA expression levels of PD-1/PD-L1 axis and immune infiltration in brain metastases, it would be worthwhile to explore the efficacy of immune checkpoint blockade for lung cancer patients with intracranial metastases.

Cholinergic neural activity directs retinal layer-specific angiogenesis and blood retinal barrier formation

Blood vessels in the central nervous system (CNS) develop unique features, but the contribution of CNS neurons to regulating those features is not fully understood. We report that inhibiting spontaneous cholinergic activity or reducing starburst amacrine cell numbers prevents invasion of endothelial cells into the deep layers of the retina and causes blood-retinal-barrier (BRB) dysfunction in mice. Vascular endothelial growth factor (VEGF), which drives angiogenesis, and Norrin, a Wnt ligand that induces BRB properties, are decreased after activity blockade. Exogenous VEGF restores vessel growth but not BRB function, whereas stabilizing beta-catenin in endothelial cells rescues BRB dysfunction but not vessel formation. We further identify that inhibiting cholinergic activity reduces angiogenesis during oxygen-induced retinopathy. Our findings demonstrate that neural activity lies upstream of VEGF and Norrin, coordinating angiogenesis and BRB formation. Neural activity originating from specific neural circuits may be a general mechanism for driving regional angiogenesis and barrier formation across CNS development.

During retinal development, waves of cholinergic neural activity play a role in retinal circuit development. Here, the authors show that this activity also contributes to layer-specific angiogenesis and formation of the blood-retinal barrier.

The Blood-Brain Barrier: Implications for Vasculitis

There has been extraordinary research in the blood-brain barrier. Once considered a static anatomic barrier to the traffic of molecules in and out of the central nervous system when fully developed in adults, the blood-brain barrier is now known to be not only fully functional in development but also vital in cerebrovascular angiogenesis. Blood-brain barrier breakdown has been recognized as an important factor in a variety of primary neurologic diseases; however, such disturbances have yet to be critically analyzed. This article reviews the history, neurodevelopment, ultrastructure, function, and clinicopathologic correlation and relevance to central nervous system vasculitis.

Overcoming the Blood-Brain Barrier: The Role of Nanomaterials in Treating Neurological Diseases

Therapies directed toward the central nervous system remain difficult to translate into improved clinical outcomes. This is largely due to the blood-brain barrier (BBB), arguably the most tightly regulated interface in the human body, which routinely excludes most therapeutics. Advances in the engineering of nanomaterials and their application in biomedicine (i.e., nanomedicine) are enabling new strategies that have the potential to help improve our understanding and treatment of neurological diseases. Herein, the various mechanisms by which therapeutics can be delivered to the brain are examined and key challenges facing translation of this research from benchtop to bedside are highlighted. Following a contextual overview of the BBB anatomy and physiology in both healthy and diseased states, relevant therapeutic strategies for bypassing and crossing the BBB are discussed. The focus here is especially on nanomaterial-based drug delivery systems and the potential of these to overcome the biological challenges imposed by the BBB. Finally, disease-targeting strategies and clearance mechanisms are explored. The objective is to provide the diverse range of researchers active in the field (e.g., material scientists, chemists, engineers, neuroscientists, and clinicians) with an easily accessible guide to the key opportunities and challenges currently facing the nanomaterial-mediated treatment of neurological diseases.

Current and Future Therapeutic Strategies for Lentiviral Eradication from Macrophage Reservoirs

Macrophages, one of the most abundant populations of leukocytes in the body, function as the first line of defense against pathogen invaders. Human Immunodeficiency virus 1 (HIV-1) remains to date one of the most extensively studied viral infections. Naturally occurring lentiviruses in domestic and primate species serve as valuable models to investigate lentiviral pathogenesis and novel therapeutics. Better understanding of the role macrophages play in HIV pathogenesis will aid in the advancement towards a cure. Even with current efficacy of first- and second-line Antiretroviral Therapy (ART) guidelines and future efficacy of Long Acting Slow Effective Release-ART (LASER-ART); ART alone does not lead to a cure. The major challenge of HIV eradication is viral latency. Latency Reversal Agents (LRAs) show promise as a possible means to eradicate HIV-1 from the body. It has become evident that complete eradication will need to include combinations of various effective therapeutic strategies such as LASER-ART, LRAs, and gene editing. Review of the current literature indicates the most promising HIV eradication strategy appears to be LASER-ART in conjunction with viral and receptor gene modifications via the CRISPR/Cas9 system. Graphical abstract A multimodal approach to HIV treatment including gene editing, LASER-ART, and latency reversal agents may provide a means to achieve HIV eradication.

Applications of the FIV Model to Study HIV Pathogenesis

Feline immunodeficiency virus (FIV) is a naturally-occurring retrovirus that infects domestic and non-domestic feline species, producing progressive immune depletion that results in an acquired immunodeficiency syndrome (AIDS). Much has been learned about FIV since it was first described in 1987, particularly in regard to its application as a model to study the closely related lentivirus, human immunodeficiency virus (HIV). In particular, FIV and HIV share remarkable structure and sequence organization, utilize parallel modes of receptor-mediated entry, and result in a similar spectrum of immunodeficiency-related diseases due to analogous modes of immune dysfunction. This review summarizes current knowledge of FIV infection kinetics and the mechanisms of immune dysfunction in relation to opportunistic disease, specifically in regard to studying HIV pathogenesis. Furthermore, we present data that highlight changes in the oral microbiota and oral immune system during FIV infection, and outline the potential for the feline model of oral AIDS manifestations to elucidate pathogenic mechanisms of HIV-induced oral disease. Finally, we discuss advances in molecular biology, vaccine development, neurologic dysfunction, and the ability to apply pharmacologic interventions and sophisticated imaging technologies to study experimental and naturally occurring FIV, which provide an excellent, but often overlooked, resource for advancing therapies and the management of HIV/AIDS.

The blood-brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by the pathological accumulation of amyloid beta (Aβ) peptides and neurofibrillary tangles containing hyperphosphorylated neuronal tau protein. AD pathology is also characterized by chronic brain inflammation, which promotes disease pathogenesis. In this context, the blood-brain barrier (BBB), a highly specialized endothelial cell membrane that lines cerebral microvessels, represents the interface between neural cells and circulating cells of the immune system. The BBB thus plays a key role in the generation and maintenance of chronic inflammation during AD. The BBB operates within the neurovascular unit (NVU), which includes clusters of glial cells, neurons and pericytes. The NVU becomes dysfunctional during AD, and each of its components may undergo functional changes that contribute to neuronal injury and cognitive deficit. In transgenic animals with AD-like pathology, recent studies have shown that circulating leukocytes migrate through the activated brain endothelium when certain adhesion molecules are expressed, penetrating into the brain parenchyma, interacting with the NVU components and potentially affecting their structural integrity and functionality. Therefore, migrating immune system cells in cerebral vessels act in concert with the modified BBB and may be integrated into the dysfunctional NVU. Notably, blocking the adhesion mechanisms controlling leukocyte-endothelial interactions inhibits both Aβ deposition and tau hyperphosphorylation, and reduces memory loss in AD models. The characterization of molecular mechanisms controlling vascular inflammation and leukocyte trafficking could therefore help to determine the basis of BBB dysfunction during AD and may lead to the development of new therapeutic approaches.

Feline Immunodeficiency Virus Neuropathogenesis: A Model for HIV-Induced CNS Inflammation and Neurodegeneration

Feline Immunodeficiency virus (FIV), similar to its human analog human immunodeficiency virus (HIV), enters the central nervous system (CNS) soon after infection and establishes a protected viral reservoir. The ensuing inflammation and damage give rise to varying degrees of cognitive decline collectively known as HIV-associated neurocognitive disorders (HAND). Because of the similarities to HIV infection and disease, FIV has provided a useful model for both in vitro and in vivo studies of CNS infection, inflammation and pathology. This mini review summarizes insights gained from studies of early infection, immune cell trafficking, inflammation and the mechanisms of neuropathogenesis. Advances in our understanding of these processes have contributed to the development of therapeutic interventions designed to protect neurons and regulate inflammatory activity.

Immune response in breast cancer brain metastases and their microenvironment: the role of the PD-1/PD-L axis

BACKGROUND

A better understanding of immune response in breast cancer brain metastases (BCBM) may prompt new preventive and therapeutic strategies.

METHODS

Immunohistochemical expression of stromal tumor-infiltrating lymphocytes (TILs: CD4, CD8, CTLA4), macrophage/microglial cells (CD68), programmed cell death protein 1 receptor (PD-1), programmed cell death protein 1 receptor ligand (PD-L)1, PD-L2 and glial fibrillary acid protein was assessed in 84 BCBM and their microenvironment.

RESULTS

Median survival after BCBM excision was 18.3 months (range 0-99). Median number of CD4+, CD8+ TILs and CD68+ was 49, 69 and 76 per 1 mm(2), respectively. PD-L1 and PD-L2 expression in BCBM was present in 53 % and 36 % of cases, and was not related to BCBM phenotype. PD-1 expression on TILs correlated positively with CD4+ and CD8+ TILs (r = 0.26 and 0.33), and so did CD68+ (r = 0.23 and 0.27, respectively). In the multivariate analysis, survival after BCBM excision positively correlated with PD-1 expression on TILs (hazard ratio (HR) = 0.3, P = 0.003), CD68+ infiltration (HR = 0.2, P < 0.001), brain radiotherapy (HR = 0.1, P < 0.001), endocrine therapy (HR = 0.1, P < 0.001), and negatively with hormone-receptor-negative/human epidermal growth factor receptor 2 (HER2)-positive phenotype of primary tumor (HR = 2.6, P = 0.01), HER2 expression in BCBM (HR = 4.9, P = 0.01).

CONCLUSIONS

PD-L1 and PD-L2 expression is a common occurrence in BCBM, irrespective of primary tumor and BCBM phenotype. Favorable prognostic impact of PD-1 expression on TILs suggests a beneficial effect of preexisting immunity and implies a potential therapeutic role of immune checkpoint inhibitors in BCBM.

From blood-brain barrier to blood-brain interface: new opportunities for CNS drug delivery

One of the biggest challenges in the development of therapeutics for central nervous system (CNS) disorders is achieving sufficient blood-brain barrier (BBB) penetration. Research in the past few decades has revealed that the BBB is not only a substantial barrier for drug delivery to the CNS but also a complex, dynamic interface that adapts to the needs of the CNS, responds to physiological changes, and is affected by and can even promote disease. This complexity confounds simple strategies for drug delivery to the CNS, but provides a wealth of opportunities and approaches for drug development. Here, I review some of the most important areas that have recently redefined the BBB and discuss how they can be applied to the development of CNS therapeutics.

The blood-brain barrier

Blood vessels are critical to deliver oxygen and nutrients to all of the tissues and organs throughout the body. The blood vessels that vascularize the central nervous system (CNS) possess unique properties, termed the blood-brain barrier, which allow these vessels to tightly regulate the movement of ions, molecules, and cells between the blood and the brain. This precise control of CNS homeostasis allows for proper neuronal function and also protects the neural tissue from toxins and pathogens, and alterations of these barrier properties are an important component of pathology and progression of different neurological diseases. The physiological barrier is coordinated by a series of physical, transport, and metabolic properties possessed by the endothelial cells (ECs) that form the walls of the blood vessels, and these properties are regulated by interactions with different vascular, immune, and neural cells. Understanding how these different cell populations interact to regulate the barrier properties is essential for understanding how the brain functions during health and disease.

Dissecting gene expression at the blood-brain barrier

The availability of genome-wide expression data for the blood-brain barrier is an invaluable resource that has recently enabled the discovery of several genes and pathways involved in the development and maintenance of the blood-brain barrier, particularly in rodent models. The broad distribution of published data sets represents a viable starting point for the molecular dissection of the blood-brain barrier and will further direct the discovery of novel mechanisms of blood-brain barrier formation and function. Technical advances in purifying brain endothelial cells, the key cell that forms the critical barrier, have allowed for greater specificity in gene expression comparisons with other central nervous system cell types, and more systematic characterizations of the molecular composition of the blood-brain barrier. Nevertheless, our understanding of how the blood-brain barrier changes during aging and disease is underrepresented. Blood-brain barrier data sets from a wider range of experimental paradigms and species, including invertebrates and primates, would be invaluable for investigating the function and evolution of the blood-brain barrier. Newer technologies in gene expression profiling, such as RNA-sequencing, now allow for finer resolution of transcriptomic changes, including isoform specificity and RNA-editing. As our field continues to utilize more advanced expression profiling in its ongoing efforts to elucidate the blood-brain barrier, including in disease and drug delivery, we will continue to see rapid advances in our understanding of the molecular mediators of barrier biology. We predict that the recently published data sets, combined with forthcoming genomic and proteomic blood-brain barrier data sets, will continue to fuel the molecular genetic revolution of blood-brain barrier biology.

Pharmacokinetics and modeling of immune cell trafficking: quantifying differential influences of target tissues versus lymphocytes in SJL and lipopolysaccharide-treated mice

BACKGROUND

Immune cell trafficking into the CNS and other tissues plays important roles in health and disease. Rapid quantitative methods are not available that could be used to study many of the dynamic aspects of immune cell-tissue interactions.

METHODS

We used pharmacokinetics and modeling to quantify and characterize the trafficking of radioactively labeled lymphocytes into brain and peripheral tissues. We used variance from two-way ANOVAs with 2 × 2 experimental designs to model the relative influences of lymphocytes and target tissues in trafficking.

RESULTS

We found that in male CD-1 mice, about 1 in 5,000 intravenously injected lymphocytes entered each gram of brain. Uptake by brain was 2 to 3 times higher in naïve SJL females, but uptake by spleen and clearance from blood was lower, demonstrating a dichotomy in immune cell distribution. Treatment of CD-1 mice with lipopolysaccharide (LPS) increased immune cell uptake into brain but decreased uptake by spleen and axillary nodes.

CONCLUSIONS

Differences in brain uptake and in uptake by spleen between SJL and CD-1 mice were primarily determined by lymphocytes, whereas differences in uptake with LPS were primarily determined by lymphocytes for the brain but by the tissues for the spleen and the axillary lymph node. These results show that immune cells normally enter the CNS and that tissues and immune cells interact in ways that can be quantified by pharmacokinetic models.

Myelin debris regulates inflammatory responses in an experimental demyelination animal model and multiple sclerosis lesions

In multiple sclerosis (MS), gray matter pathology is characterized by less pronounced inflammation when compared with white matter lesions. Although regional differences in the cytoarchitecture may account for these differences, the amount of myelin debris in the cortex during a demyelinating event might also be contributory. To analyze the association between myelin debris levels and inflammatory responses, cortical areas with distinct and sparse myelination were analyzed for micro- and astrogliosis before and after cuprizone-induced demyelination in mice. In postmortem tissue of MS patients, leucocortical lesions were assessed for the type and level of inflammation in the cortical and white matter regions of the lesion. Furthermore, mice were injected intracerebrally with myelin-enriched debris, and the inflammatory response analyzed in white and grey matter areas. Our studies show that the magnitude of myelin loss positively correlates with microgliosis in the cuprizone model. In MS, the number of MHC class II expressing cells is higher in the white compared with the grey matter part of leucocortical lesions. Finally, direct application of myelin debris into the corpus callosum or cortex of mice induces profound and comparable inflammation in both regions. Our data suggest that myelin debris is an important variable in the inflammatory response during demyelinating events. Whether myelin-driven inflammation affects neuronal integrity remains to be clarified.

Transmigration of macrophages across the choroid plexus epithelium in response to the feline immunodeficiency virus

Although lentiviruses such as human, feline and simian immunodeficiency viruses (HIV, FIV, SIV) rapidly gain access to cerebrospinal fluid (CSF), the mechanisms that control this entry are not well understood. One possibility is that the virus may be carried into the brain by immune cells that traffic across the blood-CSF barrier in the choroid plexus. Since few studies have directly examined macrophage trafficking across the blood-CSF barrier, we established transwell and explant cultures of feline choroid plexus epithelium and measured trafficking in the presence or absence of FIV. Macrophages in co-culture with the epithelium showed significant proliferation and robust trafficking that was dependent on the presence of epithelium. Macrophage migration to the apical surface of the epithelium was particularly robust in the choroid plexus explants where 3-fold increases were seen over the first 24 h. Addition of FIV to the cultures greatly increased the number of surface macrophages without influencing replication. The epithelium in the transwell cultures was also permissive to PBMC trafficking, which increased from 17 to 26% of total cells after exposure to FIV. Thus, the choroid plexus epithelium supports trafficking of both macrophages and PBMCs. FIV significantly enhanced translocation of macrophages and T cells indicating that the choroid plexus epithelium is likely to be an active site of immune cell trafficking in response to infection.

The yin and yang of microglia

Microglia, the resident immune cells of the mammalian central nervous system (CNS), play a pivotal role in both physiological and pathological conditions such as the restoration of CNS integrity and the progression of neurodegenerative disorders. Extensive data have been published that describe neuroinflammation by microglial activation to have detrimental consequences on the developing and mature brain. On the other hand, a properly directed and limited inflammatory response is known to be a natural healing process after an insult in several other tissues. Thus, it is not surprising that research results illustrating benefits of neuroinflammation have been emerging over the past decade. Inflammation-mediated benefits for CNS outcomes include mechanisms such as neuroprotection, mobilization of neural precursors for repair, remyelination and axonal regeneration. Here, we review data that highlight the dual aspects of microglia with a focus on the developing brain, i.e. as aggressors potentiating damage and as helpers in the recovery process following CNS damage.

The neuropathogenesis of feline immunodeficiency virus infection: barriers to overcome

Feline immunodeficiency virus (FIV), like human immunodeficiency virus (HIV)-1, is a neurotropic lentivirus, and both natural and experimental infections are associated with neuropathology. FIV enters the brain early following experimental infection, most likely via the blood-brain and blood-cerebrospinal fluid barriers. The exact mechanism of entry, and the factors that influence this entry, are not fully understood. As FIV is a recognised model of HIV-1 infection, understanding such mechanisms is important, particularly as HIV enters the brain early in infection. Furthermore, the development of strategies to combat this central nervous system (CNS) infection requires an understanding of the interactions between the virus and the CNS. In this review the results of both in vitro and in vivo FIV studies are assessed in an attempt to elucidate the mechanisms of viral entry into the brain.

Peripheral T cells derived from Alzheimer's disease patients overexpress CXCR2 contributing to its transendothelial migration, which is microglial TNF-alpha-dependent

The mechanism of circulating T cells entry into the brain in Alzheimer's diseases (AD) remains unclear. Here, we showed that peripheral T cells derived from AD patients overexpress CXCR2 to enhance its transendothelial migration. T cells migration through in vitro blood-brain barrier model was effectively blocked by anti-CXCR2 antibody or IL-8 (a CXCR2 ligand) RNAi in human brain microvascular endothelial cells (HBMECs). Amyloid beta (Abeta) injection in rat hippocampus upregulated CXCR2 expression accompanied with increased T cells occurrence in the brain, and this enhanced T cells entry was effectively blocked by CXCR2 antagonist. Furthermore, anti-TNF-alpha antibody blocked IL-8 production in HBMECs and T cells transendothelial migration caused by the culture supernatant of microglia treated with Abeta. Blockage of intracerebral TNF-alpha abolished the upregulation of CXCR2 in peripheral T cells and the increased T cells occurrence in the brain induced by Abeta injection in rat hippocampus. These data suggest that CXCR2 overexpression in peripheral T cells is intracerebral microglial TNF-alpha-dependent and TNF-alpha primes T cells transendothelial migration in Alzheimer's diseases.

Microglia: biology and pathology

The past 20 years have seen a gain in knowledge on microglia biology and microglia functions in disease that exceeds the expectations formulated when the microglia "immune network" was introduced. More than 10,000 articles have been published during this time. Important new research avenues of clinical importance have opened up such as the role of microglia in pain and in brain tumors. New controversies have also emerged such as the question of whether microglia are active or reactive players in neurodegenerative disease conditions, or whether they may be victims themselves. Premature commercial interests may be responsible for some of the confusion that currently surrounds microglia in both the Alzheimer and Parkinson's disease research fields. A critical review of the literature shows that the concept of "(micro)glial inflammation" is still open to interpretation, despite a prevailing slant towards a negative meaning. Perhaps the most exciting foreseeable development concerns research on the role of microglia in synaptic plasticity, which is expected to yield an answer to the question whether microglia are the brain's electricians. This review provides an analysis of the latest developments in the microglia field.

Lymphocyte migration through the blood-brain barrier (BBB) in feline immunodeficiency virus infection is significantly influenced by the pre-existence of virus and tumour necrosis factor (TNF)-alpha within the central nervous system (CNS): studies using an in vitro feline BBB model

AIMS

In human immunodeficiency virus infection, macrophage-tropic and lymphotropic viruses exist in the host. Central nervous system (CNS) infection is an early and ongoing event, important to understand when developing strategies to treat infection. Some knowledge exists on macrophage-tropic virus interactions with the blood-brain barrier (BBB), and the aim of this study was to investigate lymphotropic lentivirus interactions with the BBB.

METHODS

Interactions of the lymphotropic feline immunodeficiency virus (FIV) with an in vitro model of the feline BBB were evaluated in scenarios to mimic in vivo infections.

RESULTS

Cell-free FIV crossed the BBB in very low quantities, and in the presence of tumour necrosis factor (TNF)-alpha, BBB integrity was unaffected. However, cell-associated FIV readily crossed the BBB, but BBB integrity was not significantly altered. Transmigration of uninfected and infected lymphocytes increased in response to TNF-alpha, accompanied by a moderate disruption of barrier integrity and an upregulation of vascular cell adhesion molecule-1 rather than intercellular adhesion molecule-1. Significant enhancement of migration and disruption of BBB tight junctions occurred when infected cells and TNF-alpha were added to the brain side of the BBB and this enhancement was not mediated through additional TNF-alpha production.

CONCLUSIONS

Small quantities of virus in the brain together with TNF-alpha have the potential to stimulate greater cell and viral entry into the CNS and this is likely to involve important factors other than further TNF-alpha production. Lymphotropic lentivirus entry to the CNS is governed by many factors similar to macrophage-tropic strains.

Endothelial cell suppression of peripheral blood mononuclear cell trafficking in vitro during acute exposure to feline immunodeficiency virus

Trafficking of peripheral blood mononuclear cells (PBMCs) into the brain is a critical step in the initiation of human immunodeficiency virus (HIV)-associated central nervous system disease. To examine potential factors that control trafficking during the earliest stages of infection, PBMC transmigration across a cultured feline brain endothelial cell (BECs) monolayer was measured after selective exposure of various cell types to feline immunodeficiency virus (FIV). Infection of the PBMCs with FIV increased the trafficking of monocytes and CD4 and CD8 T cells. Additional exposure of the BECs to FIV suppressed mean monocyte, CD4 T cell, and CD8 T cell trafficking. B cell trafficking was unaltered by these changing conditions. Subsequent exposure of astrocytes or microglia to FIV altered transmigration of different PBMC subsets in different ways. Treated microglia compared with treated astrocytes decreased monocyte transmigration, whereas B cell transmigration was increased significantly. When both astrocytes and microglia were exposed to FIV, an increase in CD8 T cell transmigration relative to BECs alone, to BECs plus astrocytes, or to BECs plus microglia was demonstrated. Thus, initial exposure of PBMCs to FIV is sufficient to induce a general increase in trafficking, whereas initial exposure of endothelial cells to FIV tends to down-regulate this effect. Selectivity of trafficking of specific PBMC subsets is apparent only after exposure of cells of the central nervous system to FIV in co-culture with the endothelium.

Feline immunodeficiency virus infection: a valuable model to study HIV-1 associated encephalitis

Feline immunodeficiency virus (FIV), like human immunodeficiency virus (HIV)-1, is a neurotropic lentivirus and is associated with neuropathology in natural and experimental infections. FIV enters the brain early following experimental infection, and virus has been proposed to enter the brain via the blood-brain barrier and blood-CSF barrier, within infected lymphocytes and monocytes/macrophages. However the entry of cell-free virus or the direct infection of brain endothelial cells and astrocytes of the blood-brain barrier may also contribute to CNS infection. This review explores the role played by the FIV model in the elucidation of mechanism of lentiviral entry to the brain and viral interactions with the CNS, particularly in relation to lymphotropic lentiviruses.

Sustained generation of tissue dendritic cells from cats using organ stromal cell cultures

Currently most dendritic cells (DC) for in vitro study are generated from bone marrow or peripheral blood by culture in high concentrations of GM-CSF and other cytokines. However, in mice it is also possible to generate DC from spleen cells using long-term stromal cell cultures. To determine whether tissue DC could be also be generated from cats, we established stromal cell cultures from a number of different tissues of newborn cats. We found that stromal cell cultures from spleen, lung, liver, kidney, brain, and lymph node tissues were all capable of spontaneously generating DC over long periods of time (months), without requiring the addition of exogenous cytokines. The tissue DC generated from these stromal cell cultures could be readily isolated at high purity by simple mechanical detachment. The feline tissue DC expressed high levels of CD11c, CD11b, and MHC Class II and variable levels of CD80 and CD14 and exhibited high levels of spontaneous macropinocytosis. Moreover, DC from spleen stromal cell cultures, but not DC from lung or liver stromal cell cultures, stimulated mixed-lymphocyte reactions. The DC generated from the stromal cell cultures were relatively independent of GM-CSF for survival and proliferation, indicative of a dependence on other growth factors produced by the stromal cells. These results suggest that tissues of young cats contain a population of resident DC progenitor cells that under appropriate conditions are capable of spontaneous proliferation and generation of immature DC.

Feline immunodeficiency virus neuropathogenesis: from cats to calcium

Invasion of human immunodeficiency virus (HIV) into the central and peripheral nervous system produces a wide range of neurological symptoms, which continue to persist even with adequate therapeutic suppression of the systemic viremia. The development of therapies designed to prevent the neurological complications of HIV require a detailed understanding of the mechanisms of virus penetration into the nervous system, infection, and subsequent neuropathogenesis. These processes, however, are difficult to study in humans. The identification of animal lentiviruses similar to HIV has provided useful models of HIV infection that have greatly facilitated these efforts. This review summarizes contributions made from in vitro and in vivo studies on the infectious and pathological interactions of feline immunodeficiency virus (FIV) with the nervous system. In vivo studies on FIV have provided insights into the natural progression of CNS disease as well as the contribution of various risk factors. In vitro studies have contributed to our understanding of immune cell trafficking, CNS infection and neuropathogenesis. Together, these studies have made unique contributions to our understanding of (1) lentiviral interactions at the blood-cerebrospinal fluid (CSF) barrier within the choroid plexus, (2) early FIV invasion and pathogenesis in the brain, and (3) lentiviral effects on intracellular calcium deregulation and neuronal dysfunction. The ability to combine in vitro and in vivo studies on FIV offers enormous potential to explore neuropathogenic mechanisms and generate information necessary for the development of effective therapeutic interventions.