Inflammatory Cells In Brain Research Articles

High-density lipoprotein reduces microglia activation and protects against experimental autoimmune encephalomyelitis in mice

Studies have shown that high-density lipoprotein (HDL) is a powerful anti-atherosclerosis factor in vivo and in vitro, with anti-inflammatory effects, and it also plays an important role in the immune system and central nervous system (CNS). In this study, the BV2 microglia inflammation model and experimental autoimmune encephalomyelitis animal model were used to investigate the potential mechanism of HDL in multiple sclerosis. Our results show that HDL inhibits the activation of BV2 microglia in a model of BV2 microglia inflammation and were validated with primary microglia. HDL can down-regulate the expression of TNF-α, IL-6, iNOS and NO. Western blot results showed that HDL could reduce the expression levels of TLR4, CD14, MyD88 and NF-κB p65 LPS-induced microglia. In a mouse model of experimental autoimmune encephalomyelitis, hematoxylin-eosin (HE) staining showed decreased infiltration of inflammatory cells in brain and spinal cord tissues, and Luxol Fast Blue (LFB) staining showed significant improvement in spinal cord demyelination. We found that HDL reduced spinal cord and brain inflammation after EAE induction, inhibited the infiltration of CD68 and Iba-1 positive inflammatory cells, and reduced the production of multiple pro-inflammatory cytokines, including pro-inflammatory cytokines TNF-α, IL-6, and IL-1β. Western blot showed that EAE mice HDL inhibited the activation of ERK1/2 and JNK in MAPK pathway and p-IκBα and P65 in NF-κB pathway. Taken together, our study suggests that HDL may influence microglia activation and inflammatory response in mice by regulating inflammatory signaling pathways, improving induction of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis, and provides further insights into HDL therapy for multiple sclerosis.

Cell Senescence as a Mediator of Age-Dependent Brain Inflammation

Cellular senescence and inflammation are interconnected causes and consequences of tissue aging. Here, we implemented orthogonal approaches to study their interaction in steady-state mature and aged mouse brain. Using single cell sequencing, we identified a putative senescent microglial population, which increased in abundance with age and was characterized by increased expression of p16 and chemotactic senescence associated secretory phenotype (SASP) factors. Using p16-INK-ATTAC transgenic mice to eliminate p16ink4a-positive senescent cells and mass cytometry, we show that p16ink4a-positive cell targeting reduced the abundance of activated inflammatory cells in the aged female brain. Age-dependent declines in executive cognitive function were improved following transgenic p16ink4a-positive cell targeting, and executive function robustly correlated with inflammatory brain cell composition in females. Collectively, our findings demonstrate fundamental differences in the age- and sex-dependent brain inflammatory landscape and implicate p16ink4a-positive senescent cell targeting as a therapeutic strategy to attenuate age-related inflammation and cognitive decline.

Melatonin against acute ischaemic stroke dependently via suppressing both inflammatory and oxidative stress downstream signallings.

This study tested the hypothesis that melatonin (Mel) therapy preserved the brain architectural and functional integrity against ischaemic stroke (IS) dependently through suppressing the inflammatory/oxidative stress downstream signalling pathways. Adult male B6 (n = 6 per each B6 group) and TLR4 knockout (ie TLR4−/−) (n = 6 per each TLR4−/− group) mice were categorized into sham control (SCB6), SCTLR4−/−, ISB6, ISTLR4−/−, ISB6 + Mel (i.p. daily administration) and ISTLR4−/− + Mel (i.p. daily administration). By day 28 after IS, the protein expressions of inflammatory (HMBG1/TLR2/TLR4/MAL/MyD88/RAM TRIF/TRAF6/IKK‐α/p‐NF‐κB/nuclear‐NF‐κB/nuclear‐IRF‐3&7/IL‐1β/IL‐6/TNF‐α/IFN‐γ) and oxidative stress (NOX‐1/NOX‐2/ASK1/p‐MKK4&7/p‐JNK/p‐c‐JUN) downstream pathways as well as mitochondrial‐damaged markers (cytosolic cytochrome C/cyclophilin D/SRP1/autophagy) were highest in group ISB6, lowest in groups SCB6 and SCTLR4−/−, lower in group ISTLR4−/− + Mel than in groups ISTLR4−/− and ISB6 + Mel and lower in group ISB6 + Mel than in group ISTLR4−/− (all P < .0001). The brain infarct volume, brain infarct area and the number of inflammatory cells in brain (CD14/F4‐88) and in circulation (MPO+//Ly6C+/CD11b+//Ly6G+/CD11b+) exhibited an identical pattern, whereas the neurological function displayed an opposite pattern of inflammatory protein expression among the six groups (all P < .0001). In conclusion, TLR inflammatory and oxidative stress signallings played crucial roles for brain damage and impaired neurological function after IS that were significantly reversed by Mel therapy.

Therapy with recombinant T-cell receptor ligand reduces infarct size and infiltrating inflammatory cells in brain after middle cerebral artery occlusion in mice

Stroke induces a biphasic effect on the peripheral immune response that involves early activation of peripheral leukocytes followed by severe immunosuppression and atrophy of the spleen. Peripheral immune cells, including T lymphocytes, migrate to the brain and exacerbate the developing infarct. Recombinant T-cell receptor (TCR) Ligand (RTL)551 is designed as a partial TCR agonist for myelin oligodendrocyte glycoprotein (MOG)-reactive T cells and has demonstrated the capacity to limit infarct volume and inflammation in brain when administered to mice undergoing middle cerebral artery occlusion (MCAO). The goal of this study was to determine if RTL551 could retain protection when given within the therapeutically relevant 4 h time window currently in clinical practice for stroke patients. RTL551 was administered subcutaneously 4 h after MCAO, with repeated doses every 24 h until the time of euthanasia. Cell numbers were assessed in the brain, blood, spleen and lymph nodes and infarct size was measured after 24 and 96 h reperfusion. RTL551 reduced infarct size in both cortex and striatum at 24 h and in cortex at 96 h after MCAO and inhibited the accumulation of inflammatory cells in brain at both time points. At 24 h post-MCAO, RTL551 reduced the frequency of the activation marker, CD44, on T-cells in blood and in the ischemic hemisphere. Moreover, RTL551 reduced expression of the chemokine receptors, CCR5 in lymph nodes and spleen, and CCR7 in the blood and lymph nodes. These data demonstrate effective treatment of experimental stroke with RTL551 within a therapeutically relevant 4 h time window through immune regulation of myelin-reactive inflammatory T-cells.

Molecular mechanisms involved in T cell migration across the blood–brain barrier

In the healthy individuum lymphocyte traffic into the central nervous system (CNS) is very low and tightly controlled by the highly specialized blood-brain barrier (BBB). In contrast, under inflammatory conditions of the CNS such as in multiple sclerosis or in its animal model experimental autoimmune encephalomyelitis (EAE) circulating lymphocytes and monocytes/macrophages readily cross the BBB and gain access to the CNS leading to edema, inflammation and demyelination. Interaction of circulating leukocytes with the endothelium of the blood-spinal cord and blood-brain barrier therefore is a critical step in the pathogenesis of inflammatory diseases of the CNS. Leukocyte/endothelial interactions are mediated by adhesion molecules and chemokines and their respective chemokine receptors. We have developed a novel spinal cord window preparation, which enables us to directly visualize CNS white matter microcirculation by intravital fluorescence videomicroscopy. Applying this technique of intravital fluorescence videomicroscopy we could provide direct in vivo evidence that encephalitogenic T cell blasts interact with the spinal cord white matter microvasculature without rolling and that alpha4-integrin mediates the G-protein independent capture and subsequently the G-protein dependent adhesion strengthening of T cell blasts to microvascular VCAM-1. LFA-1 was found to neither mediate the G-protein independent capture nor the G- protein dependent initial adhesion strengthening of encephalitogenic T cell blasts within spinal cord microvessel, but was rather involved in T cell extravasation across the vascular wall into the spinal cord parenchyme. Our observation that G-protein mediated signalling is required to promote adhesion strengthening of encephalitogenic T cells on BBB endothelium in vivo suggested the involvement of chemokines in this process. We found functional expression of the lymphoid chemokines CCL19/ELC and CCL21/SLC in CNS venules surrounded by inflammatory cells in brain and spinal cord sections of mice afflicted with EAE suggesting that the lymphoid chemokines CCL19 and CCL21 besides regulating lymphocyte homing to secondary lymphoid tissue might be involved in T lymphocyte migration into the immuneprivileged CNS during immunosurveillance and chronic inflammation. Here, I summarize our current knowledge on the sequence of traffic signals involved in T lymphocyte recruitment across the healthy and inflamed blood-brain and blood-spinal cord barrier based on our in vitro and in vivo investigations.

Functional expression of the lymphoid chemokines CCL19 (ELC) and CCL 21 (SLC) at the blood-brain barrier suggests their involvement in G-protein-dependent lymphocyte recruitment into the central nervous system during experimental autoimmune encephalomyelitis.

Migration of autoaggressive T cells across the blood-brain barrier (BBB) is critically involved in the initiation of experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. The direct involvement of chemokines in this process was suggested by our recent observation that G-protein-mediated signaling is required to promote adhesion strengthening of encephalitogenic T cells on BBB endothelium in vivo. To search for chemokines present at the BBB, we performed in situ hybridizations and immunohistochemistry and found expression of the lymphoid chemokines CCL19/ELC and CCL21/SLC in venules surrounded by inflammatory cells. Their expression was paralleled by the presence of their common receptor CCR7 in inflammatory cells in brain and spinal cord sections of mice afflicted with EAE. Encephalitogenic T cells showed surface expression of CCR7 and the alternative receptor for CCL21, CXCR3. They specifically chemotaxed towards both CCL19 or CCL21 in a concentration dependent and pertussis toxin-sensitive manner comparable to naive lymphocytes in vitro. Binding assays on frozen sections of EAE brains demonstrated a functional involvement of CCL19 and CCL21 in adhesion strengthening of encephalitogenic T lymphocytes to inflamed venules in the brain. Taken together our data suggest that the lymphoid chemokines CCL19 and CCL21 besides regulating lymphocyte homing to secondary lymphoid tissue are involved in T lymphocyte migration into the immunoprivileged central nervous system during immunosurveillance and chronic inflammation.

Borna Disease Virus-Induced Neurological Disorder in Mice: Infection of Neonates Results in Immunopathology

Borna disease virus (BDV) is a neurotropic nonsegmented negative-stranded RNA virus that persistently infects warm-blooded animals. In horses and other natural animal hosts, infections with BDV cause meningoencephalitis and behavioral disturbances. Experimental infection of adult mice takes a nonsymptomatic course, an observation previously believed to indicate that this animal species is not suitable for pathogenesis studies. We now demonstrate that BDV frequently induces severe neurological disease in infected newborn mice. Signs of neurological disease were first observed 4 to 6 weeks after intracerebral infection. They included a characteristic nonphysiological position of the hind limbs at an early stage of the disease and paraparesis at a later stage. Histological examination revealed large numbers of perivascular and meningeal inflammatory cells in brains of diseased mice and, unexpectedly, no increase in immunoreactivity to glial fibrillar acidic protein. The incidence and severity of BDV-induced disease varied dramatically among mouse strains. While only 13% of the infected C57BL/6 mice showed disease symptoms, which were mostly transient, more than 80% of the infected MRL mice developed severe neurological disorder. In spite of these differences in susceptibility to disease, BDV replicated to comparable levels in the brains of mice of the various strains used. Intracerebral infections of newborn beta2-microglobulin-deficient C57BL/6 and MRL mice, which both lack CD8+ T cells, did not result in meningoencephalitis or neurological disease, indicating that the BDV-induced neurological disorder in mice is a cytotoxic T-cell-mediated immunopathological process. With this new animal model it should now be possible to characterize the disease-inducing immune response to BDV in more detail.

Immunohistochemical characterization of inflammatory cells in brains of dogs with granulomatous meningoencephalitis.

The inflammatory cells of eleven dogs with canine granulomatous meningoencephalitis were characterized immunohistochemically. Macrophages were identified by antibodies directed against lysozyme and the DH82 antigen (expressed by cells of a malignant histiocytosis). T cells were demonstrated by CD3, CD43, and CD45R antigen, and B cells by immunoglobulin G and immunoglobulin M expression. Furthermore, staining for the major histocompatibility complex (MHC) class II antigen was evaluated. Diseased animals ranged from 1 to 9 years of age. Small and medium-sized breeds were affected predominantly. Lesions were widespread and localized mainly in the brain stem, less frequently in the cerebrum or cerebellum. Alterations were represented by perivascular cuffs, parenchymal granulomas, and leptomeningeal infiltrates. Lymphocytes and macrophages comprised the dominant cell populations; their percentage varied substantially between different animals and between sections from the same individual. Immunohistochemically, the bulk of lymphocytes were CD3 antigen-positive T cells, while only a few cells were CD43 and CD45R antigen-positive or were classified as B cells. The majority of macrophages expressed both lysozyme and DH82 antigen; however, some were positive for only one antigen. MHC class II antigen-expression, observed only within and in close proximity to the lesions, was found on all inflammatory cells, pericytes/endothelial cells, and microglia. Results were negative for canine distemper virus antigen and nucleoprotein mRNA, rabies virus antigen, fungi, bacteria, and protozoal agents. This immunomorphologic study reveals that inflammatory lesions in canine granulomatous meningoencephalitis consist of a heterogeneous population of MHC class II antigen-positive macrophages and predominantly CD3 antigen-positive lymphocytes. The data suggest a T cell-mediated delayed-type hypersensitivity of an organ-specific autoimmune disease as a possible pathogenic mechanism for this unique canine brain lesion.

The inflammatory reaction of paraneoplastic ganglionitis and encephalitis: an immunohistochemical study.

To elucidate the cellular mechanisms of tissue injury in paraneoplastic states, tissues from two patients with small cell carcinoma of the lung and paraneoplastic neurological syndromes were studied. One patient had encephalitis with ganglionitis, and the other ganglionitis. Immunocytochemistry on brain and ganglia was performed using monoclonal and polyclonal antibodies. The majority of the inflammatory cells in brain and ganglia were T-cells, of both helper and cytotoxic subtypes. There were more macrophages in the inflammatory infiltrate of ganglia than in the brain of encephalitis. Major histocompatibility complex class I and II antigen expression was greater in the mononuclear cells in brain than in ganglia. There was no evidence of complement deposition and little evidence for antibody synthesizing cells. Our findings suggest a T-cell-mediated immune attack in paraneoplastic ganglionitis and encephalitis, with a greater role for macrophages in ganglionitis.