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Zou K, Deng Q, Zhang H, Huang C. Glymphatic system: a gateway for neuroinflammation. Neural Regen Res 2024; 19:2661-2672. [PMID: 38595285 PMCID: PMC11168510 DOI: 10.4103/1673-5374.391312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 09/15/2023] [Accepted: 11/09/2023] [Indexed: 04/11/2024] Open
Abstract
The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.
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Affiliation(s)
- Kailu Zou
- Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, Hunan Province, China
| | - Qingwei Deng
- Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, Hunan Province, China
| | - Hong Zhang
- Xiangya School of Medicine, Central South University, Changsha, Hunan Province, China
| | - Changsheng Huang
- Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, Hunan Province, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, Hunan Province, China
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2
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Farmen K, Tofiño-Vian M, Wellfelt K, Olson L, Iovino F. Spatio-temporal brain invasion pattern of Streptococcus pneumoniae and dynamic changes in the cellular environment in bacteremia-derived meningitis. Neurobiol Dis 2024; 195:106484. [PMID: 38583642 DOI: 10.1016/j.nbd.2024.106484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Accepted: 03/22/2024] [Indexed: 04/09/2024] Open
Abstract
Streptococcus pneumoniae (the pneumococcus) is the major cause of bacterial meningitis globally, and pneumococcal meningitis is associated with increased risk of long-term neurological sequelae. These include several sensorimotor functions that are controlled by specific brain regions which, during bacterial meningitis, are damaged by a neuroinflammatory response and the deleterious action of bacterial toxins in the brain. However, little is known about the invasion pattern of the pneumococcus into the brain. Using a bacteremia-derived meningitis mouse model, we combined 3D whole brain imaging with brain microdissection to show that all brain regions were equally affected during disease progression, with the presence of pneumococci closely associated to the microvasculature. In the hippocampus, the invasion provoked microglial activation, while the neurogenic niche showed increased proliferation and migration of neuroblasts. Our results indicate that, even before the outbreak of symptoms, the bacterial load throughout the brain is high and causes neuroinflammation and cell death, a pathological scenario which ultimately leads to a failing regeneration of new neurons.
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Affiliation(s)
- Kristine Farmen
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | | | - Katrin Wellfelt
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Lars Olson
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Federico Iovino
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
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Giannetto MJ, Gomolka RS, Gahn-Martinez D, Newbold EJ, Bork PAR, Chang E, Gresser M, Thompson T, Mori Y, Nedergaard M. Glymphatic fluid transport is suppressed by the aquaporin-4 inhibitor AER-271. Glia 2024; 72:982-998. [PMID: 38363040 PMCID: PMC11203403 DOI: 10.1002/glia.24515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 01/29/2024] [Accepted: 02/05/2024] [Indexed: 02/17/2024]
Abstract
The glymphatic system transports cerebrospinal fluid (CSF) into the brain via arterial perivascular spaces and removes interstitial fluid from the brain along perivenous spaces and white matter tracts. This directional fluid flow supports the clearance of metabolic wastes produced by the brain. Glymphatic fluid transport is facilitated by aquaporin-4 (AQP4) water channels, which are enriched in the astrocytic vascular endfeet comprising the outer boundary of the perivascular space. Yet, prior studies of AQP4 function have relied on genetic models, or correlated altered AQP4 expression with glymphatic flow in disease states. Herein, we sought to pharmacologically manipulate AQP4 function with the inhibitor AER-271 to assess the contribution of AQP4 to glymphatic fluid transport in mouse brain. Administration of AER-271 inhibited glymphatic influx as measured by CSF tracer infused into the cisterna magna and inhibited increases in the interstitial fluid volume as measured by diffusion-weighted MRI. Furthermore, AER-271 inhibited glymphatic efflux as assessed by an in vivo clearance assay. Importantly, AER-271 did not affect AQP4 localization to the astrocytic endfeet, nor have any effect in AQP4 deficient mice. Since acute pharmacological inhibition of AQP4 directly decreased glymphatic flow in wild-type but not in AQP4 deficient mice, we foresee AER-271 as a new tool for manipulation of the glymphatic system in rodent brain.
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Affiliation(s)
- Michael J. Giannetto
- Center for Translational Neuromedicine, University of Rochester Medical Center, Rochester, NY, USA
- Department of Neuroscience, University of Rochester Medical Center, Rochester, NY, USA
| | - Ryszard S. Gomolka
- Center for Translational Neuromedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Daniel Gahn-Martinez
- Center for Translational Neuromedicine, University of Rochester Medical Center, Rochester, NY, USA
| | - Evan J. Newbold
- Center for Translational Neuromedicine, University of Rochester Medical Center, Rochester, NY, USA
- Department of Neuroscience, University of Rochester Medical Center, Rochester, NY, USA
| | - Peter A. R. Bork
- Department of Physics, Technical University of Denmark, Richard Petersens Plads, 2800 Lyngby, Denmark
| | - Ethan Chang
- Center for Translational Neuromedicine, University of Rochester Medical Center, Rochester, NY, USA
| | - Michael Gresser
- Aeromics Inc., 470 James Street Suite 007, New Haven, CT 06513
| | - Trevor Thompson
- Aeromics Inc., 470 James Street Suite 007, New Haven, CT 06513
| | - Yuki Mori
- Center for Translational Neuromedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Maiken Nedergaard
- Center for Translational Neuromedicine, University of Rochester Medical Center, Rochester, NY, USA
- Center for Translational Neuromedicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
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Feng J, Ren Y, Wang X, Li X, Zhu X, Zhang B, Zhao Q, Sun X, Tian X, Liu H, Dong F, Li XL, Qi L, Wei B. Impaired meningeal lymphatic drainage in Listeria monocytogenes infection. Front Immunol 2024; 15:1382971. [PMID: 38638427 PMCID: PMC11024298 DOI: 10.3389/fimmu.2024.1382971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2024] [Accepted: 03/21/2024] [Indexed: 04/20/2024] Open
Abstract
Previous studies have demonstrated an association between lymphatic vessels and diseases caused by bacterial infections. Listeria monocytogenes (LM) bacterial infection can affect multiple organs, including the intestine, brain, liver and spleen, which can be fatal. However, the impacts of LM infection on morphological and functional changes of lymphatic vessels remain unexplored. In this study, we found that LM infection not only induces meningeal and mesenteric lymphangiogenesis in mice, but also impairs meningeal lymphatic vessels (MLVs)-mediated macromolecules drainage. Interestingly, we found that the genes associated with lymphatic vessel development and function, such as Gata2 and Foxc2, were downregulated, suggesting that LM infection may affect cellular polarization and valve development. On the other hand, photodynamic ablation of MLVs exacerbated inflammation and bacterial load in the brain of mice with LM infection. Overall, our findings indicate that LM infection induces lymphangiogenesis and may affect cell polarization, cavity formation, and valve development during lymphangiogenesis, ultimately impairing MLVs drainage.
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Affiliation(s)
- Jian Feng
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
| | - Yuanzhen Ren
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
| | - Xilin Wang
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
| | - Xiaojing Li
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
| | - Xingguo Zhu
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
| | - Baokai Zhang
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
| | - Qi Zhao
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
| | - Xiaochen Sun
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
| | - Xinxin Tian
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
| | - Hongyang Liu
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
| | - Fan Dong
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
| | - Xiu-Li Li
- Department of Cardiology, Lanzhou University Second Hospital, Lanzhou, Gansu, China
| | - Linlin Qi
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
| | - Bin Wei
- Shanghai Engineering Research Center of Organ Repair, School of Life Sciences, Shanghai University, Shanghai, China
- Institute of Geriatrics, Affiliated Nantong Hospital of Shanghai University (The Sixth People’s Hospital of Nantong), School of Medicine, Shanghai University, Nantong, China
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García-Culebras A, Cuartero MI, Peña-Martínez C, Moraga A, Vázquez-Reyes S, de Castro-Millán FJ, Cortes-Canteli M, Lizasoain I, Moro MÁ. Myeloid cells in vascular dementia and Alzheimer's disease: Possible therapeutic targets? Br J Pharmacol 2024; 181:777-798. [PMID: 37282844 DOI: 10.1111/bph.16159] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Revised: 05/10/2023] [Accepted: 05/20/2023] [Indexed: 06/08/2023] Open
Abstract
Growing evidence supports the suggestion that the peripheral immune system plays a role in different pathologies associated with cognitive impairment, such as vascular dementia (VD) or Alzheimer's disease (AD). The aim of this review is to summarize, within the peripheral immune system, the implications of different types of myeloid cells in AD and VD, with a special focus on post-stroke cognitive impairment and dementia (PSCID). We will review the contributions of the myeloid lineage, from peripheral cells (neutrophils, platelets, monocytes and monocyte-derived macrophages) to central nervous system (CNS)-associated cells (perivascular macrophages and microglia). Finally, we will evaluate different potential strategies for pharmacological modulation of pathological processes mediated by myeloid cell subsets, with an emphasis on neutrophils, their interaction with platelets and the process of immunothrombosis that triggers neutrophil-dependent capillary stall and hypoperfusion, as possible effector mechanisms that may pave the way to novel therapeutic avenues to stop dementia, the epidemic of our time. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.
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Affiliation(s)
- Alicia García-Culebras
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Departamento de Biología Celular, Facultad de Medicina, UCM, Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
| | - María Isabel Cuartero
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
| | - Carolina Peña-Martínez
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
| | - Ana Moraga
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Departamento de Biología Celular, Facultad de Medicina, UCM, Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
- Instituto de Investigación Hospital 12 de Octubre (i+12), Madrid, Spain
| | - Sandra Vázquez-Reyes
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
| | - Francisco Javier de Castro-Millán
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
| | - Marta Cortes-Canteli
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Instituto de Investigación Sanitaria Fundación Jiménez Díaz (IIS-FJD), Madrid, Spain
| | - Ignacio Lizasoain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
- Instituto de Investigación Hospital 12 de Octubre (i+12), Madrid, Spain
| | - María Ángeles Moro
- Cardiovascular Risk Factor and Brain Function Programme, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), Madrid, Spain
- Unidad de Investigación Neurovascular, Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid (UCM), Madrid, Spain
- Instituto Universitario de Investigación en Neuroquímica, UCM, Madrid, Spain
- Instituto de Investigación Hospital 12 de Octubre (i+12), Madrid, Spain
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Hussain R, Graham U, Elder A, Nedergaard M. Air pollution, glymphatic impairment, and Alzheimer's disease. Trends Neurosci 2023; 46:901-911. [PMID: 37777345 DOI: 10.1016/j.tins.2023.08.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 07/12/2023] [Accepted: 08/29/2023] [Indexed: 10/02/2023]
Abstract
Epidemiological evidence demonstrates a link between air pollution exposure and the onset and progression of cognitive impairment and Alzheimer's disease (AD). However, current understanding of the underlying pathophysiological mechanisms is limited. This opinion article examines the hypothesis that air pollution-induced impairment of glymphatic clearance represents a crucial etiological event in the development of AD. Exposure to airborne particulate matter (PM) leads to systemic inflammation and neuroinflammation, increased metal load, respiratory and cardiovascular dysfunction, and sleep abnormalities. All these factors are known to reduce the efficiency of glymphatic clearance. Rescuing glymphatic function by restricting the impact of causative agents, and improving sleep and cardiovascular system health, may increase the efficiency of waste metabolite clearance and subsequently slow the progression of AD. In sum, we introduce air pollution-mediated glymphatic impairment as an important mechanistic factor to be considered when interpreting the etiology and progression of AD as well as its responsiveness to therapeutic interventions.
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Affiliation(s)
- Rashad Hussain
- Center for Translational Neuromedicine, University of Rochester, Rochester, NY 14642, USA.
| | | | - Alison Elder
- Department of Environmental Medicine, University of Rochester, Rochester, NY 14642, USA
| | - Maiken Nedergaard
- Center for Translational Neuromedicine, University of Rochester, Rochester, NY 14642, USA; Center for Translational Neuroscience, University of Copenhagen, 2200 Copenhagen, Denmark.
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Regner-Nelke L, Ruck T, Meuth SG. [Meningitis in the Emergency Room]. Anasthesiol Intensivmed Notfallmed Schmerzther 2023; 58:322-334. [PMID: 37192640 DOI: 10.1055/a-2077-6971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
AbstractMeningitis describes an inflammation of the meninges of the brain and spinal cord, which, depending on the etiology, can be a serious disease with high lethality. The suspicion of
meningitis therefore requires rapid and adept action. In this paper, we explain the diagnostic and therapeutic approach to suspected meningitis in the emergency department.
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Generoso JS, Thorsdottir S, Collodel A, Dominguini D, Santo RRE, Petronilho F, Barichello T, Iovino F. Dysfunctional Glymphatic System with Disrupted Aquaporin 4 Expression Pattern on Astrocytes Causes Bacterial Product Accumulation in the CSF during Pneumococcal Meningitis. mBio 2022; 13:e0188622. [PMID: 36036510 PMCID: PMC9600563 DOI: 10.1128/mbio.01886-22] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 08/05/2022] [Indexed: 01/17/2023] Open
Abstract
Pneumococcal meningitis, inflammation of the meninges due to an infection of the Central Nervous System caused by Streptococcus pneumoniae (the pneumococcus), is the most common form of community-acquired bacterial meningitis globally. Aquaporin 4 (AQP4) water channels on astrocytic end feet regulate the solute transport of the glymphatic system, facilitating the exchange of compounds between the brain parenchyma and the cerebrospinal fluid (CSF), which is important for the clearance of waste away from the brain. Wistar rats, subjected to either pneumococcal meningitis or artificial CSF (sham control), received Evans blue-albumin (EBA) intracisternally. Overall, the meningitis group presented a significant impairment of the glymphatic system by retaining the EBA in the CSF compartments compared to the uninfected sham group. Our results clearly showed that during pneumococcal meningitis, the glymphatic system does not function because of a detachment of the astrocytic end feet from the blood-brain barrier (BBB) vascular endothelium, which leads to misplacement of AQP4 with the consequent loss of the AQP4 water channel's functionality. IMPORTANCE The lack of solute drainage due to a dysfunctional glymphatic system leads to an increase of the neurotoxic bacterial material in the CSF compartments of the brain, ultimately leading to brain-wide neuroinflammation and neuronal damage with consequent impairment of neurological functions. The loss of function of the glymphatic system can therefore be a leading cause of the neurological sequelae developing post-bacterial meningitis.
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Affiliation(s)
- Jaqueline S. Generoso
- Laboratory of Experimental Neurology, Graduate Program in Health Sciences, University of Southern Santa Catarina (UNESC), Criciúma, Santa Catarina, Brazil
| | - Sigrun Thorsdottir
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, Sweden
| | - Allan Collodel
- Laboratory of Experimental Pathophysiology, Graduate Program in Health Sciences, University of Southern Santa Catarina (UNESC), Criciúma, Santa Catarina, Brazil
| | - Diogo Dominguini
- Laboratory of Experimental Pathophysiology, Graduate Program in Health Sciences, University of Southern Santa Catarina (UNESC), Criciúma, Santa Catarina, Brazil
| | - Roberta R. E. Santo
- Laboratory of Experimental Pathophysiology, Graduate Program in Health Sciences, University of Southern Santa Catarina (UNESC), Criciúma, Santa Catarina, Brazil
| | - Fabricia Petronilho
- Laboratory of Experimental Neurology, Graduate Program in Health Sciences, University of Southern Santa Catarina (UNESC), Criciúma, Santa Catarina, Brazil
| | - Tatiana Barichello
- Laboratory of Experimental Pathophysiology, Graduate Program in Health Sciences, University of Southern Santa Catarina (UNESC), Criciúma, Santa Catarina, Brazil
- Translational Psychiatry Program, Faillace Department of Psychiatry and Behavioral Sciences, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Federico Iovino
- Department of Neuroscience, Karolinska Institutet, Biomedicum, Stockholm, Sweden
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Abstract
Introduction Neutrophilic granulocytes are short‐lived cells continuously circulating in the vascular system of vertebrates. They play a basic and decisive role in the innate immune defence of the hosts against all types of pathogenic microorganisms. Methods Based on a literature study, the functions of neutrophils and cells with similar functions are described. The study places special emphasis on organisms in the aquatic environment and the pathogens occurring in that particular environment. Results The evolutionary origin of this specific cell type is not clear, but its most basic traits (recognition of foreign elements, extracellular trap release, phagocytosis and elimination of ingested material) are found in phagocytes in members of evolutionary ancient invertebrate groups spanning from amoebae, sponges, sea‐anemones, mollusks (snails and mussels), arthropods (crustaceans and insects) to echinoderms (sea stars and sea urchins). Their functions as innate immune sentinels and effector cells in these groups are well described. Neutrophilic granulocytes with elongated and lobed nuclei (possibly allowing cell movements through narrow extracellular spaces and leaving space for phagosomes) occur in vertebrates including fish, amphibians, reptiles, birds and mammals although the morphology of the nucleus, stainability of cytoplasmic granula, and the antimicrobial armament vary among groups. Following the pathogen invasion of a fish host, the neutrophils migrates from the vascular system into the infection focus. They apply their PRRs (including TLRs) to recognize the invader as non‐self, produce netosis by casting extracellular chromatin containing traps in the microenvironment. These nets assist the immobilization of invading microbes and prevents their further spread. The cells attach to and engulf the microbes by phagocytosis, whereafter they eliminate the pathogen in phagolysosomes equipped with a range of killing mechanisms and attract, by release of chemokines, additional immune cells (monocytes, macrophages and lymphocytes) to the site of invasion. Their role in innate immunity of fish hosts towards aquatic pathogens has been elucidated by in vivo and in vitro studies. Neutrophils interact with virus (e.g. IPNV and VHSV), bacteria (e.g. Aeromonas, Vibrio, Edwardsiella, Mycobacterium and Renibacterium) and parasites, including monogeneans (Gyrodactylus), cestodes (Diphyllobothrium), trematodes (Diplostomum) and ciliates (Ichthyophthirius and Philasterides). Despite the decisive function of neutrophils in innate immunity and early protection, the excessive production of ROS, RNS and NETs may lead to pathological disturbances in the host, which are exacerbated if the pathogens evolve immune evasion mechanisms. Conclusion Neutrophils in aquatic organisms play a central role in innate immunity but may serve as a toll and a support in acquired protection. The strong impact of the cellular reactions not only on pathogen but also on host tissues emphasizes that an optimal immune reaction is balanced, involves targeted and specific effector mechanisms, which leaves a minimum of collateral damage in host organs.
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Affiliation(s)
- Kurt Buchmann
- Laboratory of Aquatic Pathobiology, Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
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