Phagocytosis Of Cellular Debris Research Articles

L-PGDS-PGD2-DP1 Axis Regulates Phagocytosis by CD36+ MGs/MΦs That Are Exclusively Present Within Ischemic Areas After Stroke.

Brain injuries, such as ischemic stroke, cause cell death. Although phagocytosis of cellular debris is mainly performed by microglia/macrophages (MGs/MΦs), excessive accumulation beyond their phagocytic capacities results in waste product buildup, delaying brain cell regeneration. Therefore, it is essential to increase the potential for waste product removal from damaged brains. Lipocalin-type prostaglandin D synthase (L-PGDS) is the primary synthase for prostaglandin D2 (PGD2) and has been reported as a scavenger of waste products. However, the mechanism by which the L-PGDS-PGD2 axis exerts such an effect remains unelucidated. In this study, using a mouse model of ischemic stroke, we found that L-PGDS and its downstream signaling pathway components, including PGD2 and PGD2 receptor DP1 (but not DP2), were significantly upregulated in ischemic areas. Immunohistochemistry revealed the predominant expression of L-PGDS in the leptomeninges of ischemic areas and high expression levels of DP1 in CD36+ MGs/MΦs that were specifically present within ischemic areas. Furthermore, PGD2 treatment promoted the conversion of MGs/MΦs into CD36+ scavenger types and increased phagocytic activities of CD36+ MGs/MΦs. Because CD36+ MGs/MΦs specifically appeared within ischemic areas after stroke, our findings suggest that the L-PGDS-PGD2-DP1 axis plays an important role in brain tissue repair by regulating phagocytic activities of CD36+ MGs/MΦs.

Molecular mechanisms underlying microglial sensing and phagocytosis in synaptic pruning.

Microglia are the main non-neuronal cells in the central nervous system that have important roles in brain development and functional connectivity of neural circuits. In brain physiology, highly dynamic microglial processes are facilitated to sense the surrounding environment and stimuli. Once the brain switches its functional states, microglia are recruited to specific sites to exert their immune functions, including the release of cytokines and phagocytosis of cellular debris. The crosstalk of microglia between neurons, neural stem cells, endothelial cells, oligodendrocytes, and astrocytes contributes to their functions in synapse pruning, neurogenesis, vascularization, myelination, and blood-brain barrier permeability. In this review, we highlight the neuron-derived "find-me," "eat-me," and "don't eat-me" molecular signals that drive microglia in response to changes in neuronal activity for synapse refinement during brain development. This review reveals the molecular mechanism of neuron-microglia interaction in synaptic pruning and presents novel ideas for the synaptic pruning of microglia in disease, thereby providing important clues for discovery of target drugs and development of nervous system disease treatment methods targeting synaptic dysfunction.

Single-cell microglial transcriptomics during demyelination defines a microglial state required for lytic carcass clearance

BackgroundMicroglia regulate the response to injury and disease in the brain and spinal cord. In white matter diseases microglia may cause demyelination. However, how microglia respond and regulate demyelination is not fully understood.MethodsTo understand how microglia respond during demyelination, we fed mice cuprizone—a potent demyelinating agent—and assessed the dynamics of genetically fate-mapped microglia. We then used single-cell RNA sequencing to identify and track the microglial subpopulations that arise during demyelination. To understand how microglia contribute to the clearance of dead oligodendrocytes, we ablated microglia starting at the peak of cuprizone-induced cell death and used the viability dye acridine orange to monitor apoptotic and lytic cell morphologies after microglial ablation. Lastly, we treated serum-free primary microglial cultures to model distinct aspects of cuprizone-induced demyelination and assessed the response.ResultsThe cuprizone diet generated a robust microglial response by week 4 of the diet. Single-cell RNA sequencing at this time point revealed the presence of several cuprizone-associated microglia (CAM) clusters. These clusters expressed a transcriptomic signature indicative of cytokine regulation and reactive oxygen species production with altered lysosomal and metabolic changes consistent with ongoing phagocytosis. Using acridine orange to monitor apoptotic and lytic cell death after microglial ablation, we found that microglia preferentially phagocytose lytic carcasses. In culture, microglia exposed to lytic carcasses partially recapitulated the CAM state, suggesting that phagocytosis contributes to this distinct microglial state during cuprizone demyelination.ConclusionsMicroglia serve multiple roles during demyelination, yet their transcriptomic state resembles other neurodegenerative conditions. The phagocytosis of cellular debris is likely a universal cause for a common neurodegenerative microglial state.

A review article: The mysterious pericytes

Blood vessels are composed of two types of interacting cells. Endothelial cells form the inner lining of the vessel wall, and perivascular cells referred to as pericytes, vascular smooth muscle cells or mural cells which envelop the surface of the vascular tube. They are also called Rouget cells after their discoverer, Charles Rouget. Electron-microscope analyses first revealed the morphological character of pericytes. In general, pericytes possess a cell body with a prominent nucleus and a small content of cytoplasm with several long processes embracing the abluminal endothelium wall. They are embedded within the basement membrane of microvessels, which is formed by pericytes and endothelial cells. Pericytes play an integral role in the maintenance of the blood–brain barrier as well as several other homeostatic and hemostatic functions of the brain. These cells are also a key component of the neurovascular unit, which includes endothelial cells, astrocytes, and neurons. Pericytes provide a variety of functions such as capillary blood flow regulation, clearance and phagocytosis of cellular debris, angiogenesis formation of new blood vessels and regulating blood–brain barrier permeability. Recently, pericytes have gained new attention as functional and critical involvement to tumor angiogenesis and progression. Therefore as potential new targets for antiangiogenic therapies. Pericytes are complex. Their ontogeny is not completely understood, and they perform various functions throughout the body. This review article describes the current knowledge about the nature of pericytes and their functions during blood vessel growth, vessel maintenance, and pathological angiogenesis.

Diminished LC3-Associated Phagocytosis by Huntington's Disease Striatal Astrocytes.

Background:In recent years the functions of astrocytes have shifted from conventional supportive roles to also include active roles in altering synapses and engulfment of cellular debris. Recent studies have implicated astrocytes in both protective and pathogenic roles impacting Huntington’s disease (HD) progression.Objective:The goal of this study is to determine if phagocytosis of cellular debris is compromised in HD striatal astrocytes.Methods:Primary adult astrocytes were derived from two HD mouse models; the fast-progressing R6/2 and slower progressing Q175. With the use of laser nanosurgery, a single astrocyte was lysed within an astrocyte network. The phagocytic response of astrocytes was observed with phase contrast and by fluorescence microscopy for GFP-LC3 transiently transfected cells.Results:Astrocyte phagocytosis was significantly diminished in primary astrocytes, consistent with the progression of HD in R6/2 and Q175 mouse models. This was defined by the number of astrocytes responding via phagocytosis and by the average number of vesicles formed per cell. GFP-LC3 was found to increasingly localize to phagocytic vesicles over a 20-min imaging period, but not in HD mice, suggesting the involvement of LC3 in astrocyte phagocytosis.Conclusion:We demonstrate a progressive decrease in LC3-associated phagocytosis in HD mouse striatal astrocytes.

Senescence and autophagy in usual interstitial pneumonia of different etiology

Idiopathic pulmonary fibrosis (IPF) is a disease with a dismal prognosis. Currently, the causing agent(s) are poorly understood. Recent data suggest that senescence and autophagy might play a role in its development, as well as changes in metabolism due to hypoxic conditions. In this study, the expression of senescence markers in 23 cases of usual interstitial pneumonia (UIP)/IPF and UIP/chronic autoimmune diseases (UIP/AuD) was investigated. The status of autophagy was evaluated with respect to either antiinflammatory or antihypoxia function. Formalin-fixed paraffin-embedded tissues of UIP were selected for immunohistochemistry with antibodies for p21, p16, and β-galactosidase (senescence); for LC3, SIRT1, MAP1S, and pAMKα (autophagy); and for LDH and GLUT1 (metabolism). Epithelial cells in cystic remodeled areas of UIP stained for p16 and p21, p16 being more specific compared with p21. Myofibroblasts were negative in all cases. An upregulation of all four autophagy markers was seen not only in epithelia within remodeled areas and proliferating myofibroblasts, but also in bronchial epithelia and pneumocytes. Upregulated autophagy points to a compensatory mechanism for hypoxia; therefore, LDH and GLUT1 were investigated. Their expression was present in epithelia within cystic remodeling and in myofibroblasts. The cells within the remodeled areas stained for cytokeratin 5, but coexpressed TTF1, confirming their origin from basal cells of bronchioles. Within this population, senescent cells arise. Our results indicated that autophagy in UIP very likely helps cells to survive in hypoxic condition. By phagocytosis of cellular debris, they supplement their need for nutrition, and by upregulating LDH and GLUT1, they compensate for local hypoxia.

The effects of statins on microglial cells to protect against neurodegenerative disorders: A mechanistic review.

Microglia are the primary innate immune system cells in the central nervous system (CNS). They are crucial for the immunity, neurogenesis, synaptogenesis, neurotrophic support, phagocytosis of cellular debris, and maintaining the CNS integrity and homeostasis. Invasion by pathogens as well as in CNS injuries and damages results in activation of microglia known as microgliosis. The activated microglia have the capacity to release proinflammatory mediators leading to neuroinflammation. However, uncontrolled neuroinflammation can give rise to various neurological disorders (NDs), especially the neurodegenerative diseases including Parkinson's disease (PD) and related disorders, Alzheimer's disease (AD) and other dementias, multiple sclerosis (MS), Huntington's disease (HD), spinocerebellar ataxia (SCA), spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS), and stroke. Statins (HMG-CoA reductase inhibitors) are among the most widely prescribed medications for the management of hypercholesterolemia worldwide. It can be used for primary prevention in healthy individuals who are at higher risk of cardiovascular and coronary heart diseases as well as the secondary prevention in patients with cardiovascular and coronary heart diseases disease. A growing body of evidence has indicated that statins have the potential to attenuate the proinflammatory mediators and subsequent NDs by controlling the microglial activation and consequent reduction in neuroinflammatory mediators. In this review, we have discussed the recent studies on the effects of statins on microglia activation and neuroinflammation.

Focal/multifocal and geographic retinal dysplasia in the dog-In vivo retinal microanatomy analyses.

To examine the in vivo microanatomy of retinal folds and geographic lesions in dogs with acquired or inherited retinal dysplasia. Thirteen dogs had retinal microanatomy evaluation under general anesthesia using cSLO/sdOCT; two eyes had noninherited multifocal retinal folds, five had inherited multifocal retinal folds (drd1 or drd2), and 10 geographic retinal dysplasia. Retinas from two drd2 carrier dogs were examined by histology and immunohistochemistry (IHC) after in vivo imaging. Retinal folds are the common feature of acquired focal/multifocal or geographic retinal dysplasia, are indistinguishable structurally from those associated with syndromic oculoskeletal dysplasia, and represent outer nuclear layer invaginations and rosettes visible by sdOCT. In dogs heterozygous for oculoskeletal dysplasia, the folds form clusters in a perivascular distribution along superior central vessels. IHC confirmed photoreceptor identity in the retinal folds. The geographic dysplasia plaques are not focally detached, but have inner retinal disorganization and intense autofluorescence in cSLO autofluorescence mode that is mainly limited to the geographic lesion, but is not uniform and in some extends beyond the plaques. We propose that the autofluorescent characteristic of the geographic lesions is associated with an inner retinal disruption associated with perivascular or infiltrating macrophages and phagocytosis of cellular debris. As well, we suggest restructuring the examination forms to distinguish the folds that are sporadically distributed from those that have a perivascular distribution as the latter likely represent carriers for drd. In this latter group, DNA testing would be a helpful tool to provide specific breeding advice.

Lipoic Acid Treatment after Brain Injury: Study of the Glial Reaction

After trauma brain injury, oxidative substances released to the medium provoke an enlargement of the initial lesion, increasing glial cell activation and, occasionally, an influx of immune cells into the central nervous system, developing the secondary damage. In response to these stimuli, microglia are activated to perform upregulation of intracellular enzymes and cell surface markers to propagate the immune response and phagocytosis of cellular debris. The phagocytosis of debris and dead cells is essential to limit the inflammatory reaction and potentially prevent extension of the damage to noninjured regions. Lipoic acid has been reported as a neuroprotectant by acting as an antioxidant and anti-inflammatory agent. Furthermore, angiogenic effect promoted by lipoic acid has been recently shown by our group as a crucial process for neural regeneration after brain injury. In this work, we focus our attention on the lipoic acid effect on astroglial and microglial response after brain injury.

Differential Ly-6C expression identifies the recruited macrophage phenotype, which orchestrates the regression of murine liver fibrosis

Although macrophages are widely recognized to have a profibrotic role in inflammation, we have used a highly tractable CCl(4)-induced model of reversible hepatic fibrosis to identify and characterize the macrophage phenotype responsible for tissue remodeling: the hitherto elusive restorative macrophage. This CD11B(hi) F4/80(int) Ly-6C(lo) macrophage subset was most abundant in livers during maximal fibrosis resolution and represented the principle matrix metalloproteinase (MMP) -expressing subset. Depletion of this population in CD11B promoter-diphtheria toxin receptor (CD11B-DTR) transgenic mice caused a failure of scar remodeling. Adoptive transfer and in situ labeling experiments showed that these restorative macrophages derive from recruited Ly-6C(hi) monocytes, a common origin with profibrotic Ly-6C(hi) macrophages, indicative of a phenotypic switch in vivo conferring proresolution properties. Microarray profiling of the Ly-6C(lo) subset, compared with Ly-6C(hi) macrophages, showed a phenotype outside the M1/M2 classification, with increased expression of MMPs, growth factors, and phagocytosis-related genes, including Mmp9, Mmp12, insulin-like growth factor 1 (Igf1), and Glycoprotein (transmembrane) nmb (Gpnmb). Confocal microscopy confirmed the postphagocytic nature of restorative macrophages. Furthermore, the restorative macrophage phenotype was recapitulated in vitro by the phagocytosis of cellular debris with associated activation of the ERK signaling cascade. Critically, induced phagocytic behavior in vivo, through administration of liposomes, increased restorative macrophage number and accelerated fibrosis resolution, offering a therapeutic strategy to this orphan pathological process.

Microglia as modulators of cognition and neuropsychiatric disorders

It has become evident recently only that microglia are not only responsible for immunomodulatory functions in the brain but represent vital components of the larger synaptic formation, which also includes pre and postsynaptic neurones as well as astrocytes. Microglia critically contribute to CNS homeostasis by their actions in phagocytosis of cellular debris, release of a variety of cell signaling factors including neurotrophins and extracellular matrix components and direct contact with neurons. The purpose of this review is to summarize our current understanding of the involvement of microglia in cognitive processes and neuropsychiatric disorders including schizophrenia, bipolar disorder, depression, and Rett syndrome and to outline their potential signaling mechanisms in this context.

Microglia and Drug-Induced Plasticity in Reward-Related Neuronal Circuits

Drugs of abuse result in complex changes in neurocircuit of reward and stress. Whilst most of these changes affect neurons, the role of additional cell types, such as glia, in the development of tolerance and related neuroplastic changes during drug taking, addiction, and withdrawal is also emerging. For instance, astrocytes, which play an essential role in glutamatergic neurotransmission, as well as in energetic and growth factor support of neurons, are significantly affected by drugs of abuse (Miguel-Hidalgo, 2009). Furthermore, the role of microglia in tailoring neuronal connectivity, transmitter metabolism, and drug-induced neuroinflammation might also be important in physiology of neurons at the addiction-related brain circuitries. Microglia belong to monocyte/macrophage linage and are resident cells of the innate immune system in the brain. Microglia have at least three, functionally and morphologically distinct forms (Papaleo et al., 2008; Olah et al., 2011). Under normal conditions (1) resting microglia, through their highly mobile filopodia continuously survey the brain parenchyma (Nimmerjahn et al., 2005). Microglia became activated (2) in response to various danger signals posed by neurons and/or astrocytes (Davalos et al., 2005). At this stage, microglia are recruited and have local protective effects via regulated release of cytokines and phagocytosis of cellular debris. At certain point however, microglia gain reactive phenotype (3) characterized by uncontrolled release of inflammatory mediators. These cells furiously attack neurons, became neurotoxic and extend the damage (Banati and Graeber, 1994). It is noteworthy that different insults may converge upon microglial cell population and potentiate each other to worsen the outcome of the response (Zou et al., 2011). However, like macrophages, microglial cells are functionally polarized into different phenotypic activation states, referred as classical (M1) and alternative (M2). Alternatively activated microglia express anti-inflammatory cytokines and involved in tissue protection and repair. Activated microglia may contribute to addiction-related neuroplastic changes by several ways, such as release of proinflammatory cytokines, synaptic remodeling, neurochemical interaction with excitatory transmission and phagocytosis of newborn neurons and cellular debris.

Functional dissimilarity of melanomacrophage centres in the liver and spleen from females of the teleost fish Prochilodus argenteus

Melanomacrophage centres (MMCs) are formed by macrophage aggregates containing pigments such as hemosiderin, melanin and lipofuscin. MMCs are found in animals such as reptiles, amphibians and, mainly, fishes, in organs such as the kidney, spleen, thymus and liver. In teleost fish, several functions have been attributed to MMCs, including the capture and storage of cations, the phagocytosis of cellular debris and immunological reactions. As the use of MMCs has been suggested as a tool for the assessment of environmental impacts, our aim has been to describe the various metabolic processes performed by MMCs in diverse organs (liver and spleen) by using the teleost Prochilodus argenteus as an animal model. MMCs from the liver and spleen were assessed by histochemistry, transmission electron microscopy, scanning electron microscopy, X-ray microanalysis techniques and biochemical assay for N-acetylglucosaminidase activity. The data showed metabolic differences in MMCs between the liver and spleen of P. argenteus in their morphometric characteristics and biochemical and elemental composition. The implications of these findings are discussed, focusing on their role in organ metabolism.

This exemplary video shows phagocytosis of cellular debris by microglia: Movie 87_4.

This exemplary video shows phagocytosis of cellular debris by microglia: Movie 87_4.

Novel Characterization of Monocyte-Derived Cell Populations in the Meninges and Choroid Plexus and Their Rates of Replenishment in Bone Marrow Chimeric Mice

The mouse dura mater, pia mater, and choroid plexus contain resident macrophages and dendritic cells (DCs). These cells participate in immune surveillance, phagocytosis of cellular debris, uptake of antigens from the surrounding cerebrospinal fluid and immune regulation in many pathologic processes. We used Cx3cr1 knock-in, CD11c-eYFP transgenic and bone marrow chimeric mice to characterize the phenotype, density and replenishment rate of monocyte-derived cells in the meninges and choroid plexus and to assess the role of the chemokine receptor CX3CR1 on their number and tissue distribution. Iba-1 major histocompatibility complex (MHC) Class II CD169 CD68 macrophages and CD11c putative DCs were identified in meningeal and choroid plexus whole mounts. Comparison of homozygous and heterozygous Cx3cr1 mice did not reveal CX3CR1-dependancy on density, distribution or phenotype of monocyte-derived cells. In turnover studies, wild type lethally irradiated mice were reconstituted with Cx3cr1/-positive bone marrow and were analyzed at 3 days, 1, 2, 4 and 8 weeks after transplantation. There was a rapid replenishment of CX3CR1-positive cells in the dura mater (at 4 weeks) and the choroid plexus was fully reconstituted by 8 weeks. These data provide the foundation for future studies on the role of resident macrophages and DCs in conditions such as meningitis, autoimmune inflammatory disease and in therapies involving irradiation and hematopoietic or stem cell transplantation.

The ENTH domain protein Clint1 is required for epidermal homeostasis in zebrafish

Epidermal hyperproliferation and inflammation are hallmarks of the human condition psoriasis. Here, we report that a zebrafish line with a mutation in the cargo adaptor protein Clint1 exhibits psoriasis-like phenotypes including epithelial hyperproliferation and leukocyte infiltration. Clint1 is an ENTH domain-containing protein that binds SNARE proteins and functions in vesicle trafficking; however, its in vivo function in animal models has not been reported to date. The clint1 mutants exhibit chronic inflammation characterized by increased Interleukin 1beta expression, leukocyte infiltration, bidirectional trafficking and phagocytosis of cellular debris. The defects in clint1 mutants can be rescued by expression of zebrafish clint1 and can be phenocopied with clint1-specific morpholinos, supporting an essential role for Clint1 in epidermal development. Interaction studies suggest that Clint1 and Lethal giant larvae 2 function synergistically to regulate epidermal homeostasis. Accordingly, clint1 mutants show impaired hemidesmosome formation, loss of cell-cell contacts and increased motility suggestive of epithelial to mesenchymal transition. Taken together, our findings describe a novel function for the ENTH domain protein Clint1 in epidermal development and inflammation and suggest that its deficiency in zebrafish generates a phenotype that resembles the human condition psoriasis.

CD11d expression is dramatically increased in white adipose tissue of obese rodents

Macrophages (MΦ) infiltrate white adipose tissue (WAT) with increasing adiposity and are primarily localized to necrotic adipocytes. Mechanisms underlying WAT MΦ recruitment, tissue migration/retention, and function in obese animals is unclear. Integrins are cell adhesion proteins critical for leukocyte extravasation, migration, and phagocytosis. CD11d encodes the α‐subunit of the integrin αDβ2 and is expressed predominantly on monocytes/MΦ; however, its role in systemic and WAT inflammation is poorly understood. We have demonstrated for the first time that CD11d expression in retroperitoneal (RP) WAT is increased dramatically (by >200 fold) in obese female Zucker rats (n=7) compared to lean controls (n=9), further confirmed in a polygenic obese SD male rat model (~70 fold). To assess whether this upregulation in WAT is the result of obesity‐induced inflammation or generalized inflammation outside the context of obesity, we measured CD11d expression in RP WAT of non‐obese mice administered lipopolysaccharide (LPS) at 0.5 mg/kg (5 day; n=5) vs. vehicle‐treated controls. CD11d expression was increased by LPS treatment, but the fold increase (~3.6 fold) was far less than observed in obesity. Our results are consistent with the hypothesis that CD11d plays a critical role in WAT MΦ migration, tissue retention, and or phagocytosis of cellular debris and lipid from necrotic adipocytes in obesity.Grant Funding SourceWestern Human Nutrition Research Center

Temporal Patterns of Microglial Activation When Bilirubin Enters into the Brain

Event Abstract Back to Event Temporal Patterns of Microglial Activation When Bilirubin Enters into the Brain Sandra L. Silva1, Catarina C. Osório1, Ana R. Vaz1, Andreia Barateiro1, Ana S. Falcão1, Maria A. Brito1, Adelaide Fernandes1, Rui F. Silva1 and Dora Brites1* 1 University of Lisbon, Centro de Patogénese Molecular/iMed.UL, Faculty of Pharmacy, Portugal Microglia turns into an activated state when facing injury and disease entailing two main functions: phagocytosis of cellular debris and propagation of immune response. Once unconjugated bilirubin (UCB) increases proinflammatory cytokine secretion by both astrocytes [1] and microglia [2], we aimed to assess the sequence of events involved in microglia immunophenotype by UCB.Primary cultures of rat microglia were incubated from 15 min to 24 h with 50 μM UCB plus 100 μM HSA, at 37ºC. Phagocytic capacity was evaluated by fluorescent microspheres uptake. NF-κB nuclear translocation was assessed by immunocytochemistry. Activation of MAPKs (p38, ERK1/2), and upregulation of COX-2 and RAGE were determined by Western blot. Apoptosis was estimated by measuring caspase 3, 8 and 9 activities.UCB led to activation of p38 and ERK1/2 peaking between 15-30 min (≈1.3-fold, p<0.05) followed by NF-κB nuclear translocation (≈1.4-fold, p<0.05) at 1 to 2 h of exposure. These events precede the release of proinflammatory cytokines already observed. Interestingly, phagocytic properties of cells exposed to UCB was only observed at 4 h (≈1.5 -fold, p<0.05). From this point on, onset of apoptosis occurs based on the activation of caspases-3, -8 and -9 achieving a maximum increase at 12 h (≈2.3-fold, p<0.05). From 12 to 24 h of microglia exposure to UCB, a COX-2 increased expression was noticed (≈1.15-fold, p<0.01 and ≈1.14-fold, p<0.05, respectively) indicating its involvement in the immunostimulation by UCB. Although at a less extent, RAGE expression is also induced at the same time points (≈1.1-fold, p<0.05 and ≈1.14-fold, p<0.05, respectively) reinforcing the acquirement of macrophage-like properties. Since it is known that amplification of inflammatory response may result from RAGE engagement by ligands such as S100B, usually released by reactive astrocytes, it will be interesting to evaluate, in future studies, whether UCB-induced activation of astrocytes may aggravate microglial response.In conclusion, these results suggest that microglia, when facing UCB, could initially play a repair role by removing dead cells before acquiring a predominantly immunostimulant phenotype. To what extent these data can be transferred into therapy of bilirubin encephalopathy is to be shown in the future.Funded by FCT-PPCDT/SAU-MMO/55955/2004 and FCT-PTDC/SAU-NEU/64385/2006 (to DB)

Microglia Biology in Health and Disease

Microglia cells are resident central nervous system (CNS) leukocytes that regulate innate immunity and participate in adaptive immune responses in CNS tissue. However, microglia cells also appear to play an important role during normal function of the mature nervous system. In response to injury, ischemia, and inflammatory stimuli, microglia cells assume an activated phenotype associated with proliferation, migration to the site of injury, phagocytosis of cellular debris, and elaboration (Power and Proudfoot 2001) of both neurotoxic and neurotrophic factors. Recent reports strongly suggest that regulating microglia function may be a fruitful future therapeutic target for the prevention of neurological dysfunction in a variety of CNS injuries and chronic diseases. Thus, developing a thorough understanding of extracellular signals that activate microglia as well as a complete catalogue of microglia responses to activating stimuli in both the healthy and diseased state are crucial scientific endeavors. This review presents the current understanding of the biology of microglia during normal CNS function as well as in response to CNS injury or neurodegenerative disease. In addition, microglia modulate both the activation and down-regulation of the adaptive immune response in the CNS. Evidence that microglia cells play a primary role in regulating CNS immune responses will also be discussed.

Chaperon and Adjuvant Activity of hsp70: Different Natural Killer Requirement for Cross-Priming of Chaperoned and Bystander Antigens

Heat shock proteins (HSP) convey both chaperoned propeptide and danger signal to dendritic cells (DC). However, few studies have compared the two activities. Using a murine inducible hsp70 secreted by cells distinct from those providing the tumor antigens, we showed that hsp70 exerts efficacious adjuvant effects toward DC cross-priming. Hsp70 induces DC maturation and phagocytosis of cellular debris both in vitro and in vivo, which are conducive to CTL response to chaperoned and nonchaperoned antigens. Whereas the ability of hsp70 to induce cross-presentation of chaperoned peptides is natural killer (NK) independent, the adjuvant activity requires NK cells at the site of DC-hsp70 interaction to induce CTL response and therapeutic effect against lung metastases. However, although bystander activity provides equal CTL induction, the best therapeutic efficacy rests on cell vaccine secreting hsp70 that combines chaperoned antigen and danger signal within the same cell.