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Eaton P, do Amaral CP, Couto SCP, Oliveira MS, Vasconcelos AG, Borges TKS, Kückelhaus SAS, Leite JRSA, Muniz-Junqueira MI. Atomic Force Microscopy Is a Potent Technique to Study Eosinophil Activation. Front Physiol 2019; 10:1261. [PMID: 31632296 PMCID: PMC6781654 DOI: 10.3389/fphys.2019.01261] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Accepted: 09/17/2019] [Indexed: 12/18/2022] Open
Abstract
Eosinophils are multifunctional cells with several functions both in healthy individuals, and those with several diseases. Increased number and morphological changes in eosinophils have been correlated with the severity of an acute asthma exacerbation. We measured eosinophils obtained from healthy controls and individuals with acute asthma using atomic force microscopy (AFM). In the control samples, cells showed more rounded morphologies with some spreading, while activated cells from symptomatic individuals were spreading, and presenting emission of multiple pseudopods. Eosinophils presenting separate granules close to the cells suggesting some degranulation was also increased in asthma samples. In comparison to histopathological techniques based on brightfield microscopy, AFM showed considerably more details of these morphological changes, making the technique much more sensitive to detect eosinophil morphological changes that indicate functional alteration of this cell. AFM could be an important tool to evaluate diseases with alterations in eosinophil functions.
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Affiliation(s)
- Peter Eaton
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal.,LAQV-REQUIMTE, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Porto, Portugal
| | - Constança Pais do Amaral
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal
| | - Shirley C P Couto
- Laboratory of Cellular Immunology, Pathology Area, Faculty of Medicine, University of Brasília, Brasília, Brazil
| | - Mariangela S Oliveira
- Laboratory of Cellular Immunology, Pathology Area, Faculty of Medicine, University of Brasília, Brasília, Brazil
| | - Andreanne G Vasconcelos
- Research Center in Morphology and Applied Immunology, Morphology Area, Faculty of Medicine, University of Brasília, Brasília, Brazil
| | - Tatiana K S Borges
- Laboratory of Cellular Immunology, Pathology Area, Faculty of Medicine, University of Brasília, Brasília, Brazil
| | - Selma A S Kückelhaus
- Research Center in Morphology and Applied Immunology, Morphology Area, Faculty of Medicine, University of Brasília, Brasília, Brazil
| | - José Roberto S A Leite
- Research Center in Morphology and Applied Immunology, Morphology Area, Faculty of Medicine, University of Brasília, Brasília, Brazil
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2
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Melo RCN, Weller PF. Contemporary understanding of the secretory granules in human eosinophils. J Leukoc Biol 2018; 104:85-93. [PMID: 29749658 DOI: 10.1002/jlb.3mr1217-476r] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 02/14/2018] [Accepted: 02/16/2018] [Indexed: 12/12/2022] Open
Abstract
Eosinophil secretory (specific) granules have a unique morphology and are both a morphologic hallmark of eosinophils and fundamental to eosinophil-mediated responses. Eosinophil mediators with multiple functional activities are presynthesized and stored within these granules, poised for very rapid, stimulus-induced secretion. The structural organization and changes of eosinophil specific granules are revealing in demonstrating the complex and diverse secretory activities of this cell. Here, we review our current knowledge on the architecture, composition, and function of eosinophil specific granules as highly elaborated organelles able to produce vesiculotubular carriers and to interplay with the intracellular vesicular trafficking. We reconsider prior identifications of eosinophil cytoplasmic granules, including "primary," "secondary," "microgranules," and "small granules"; and consonant with advances, we provide a contemporary recognition that human eosinophils contain a single population of specific granules and their developmental precursors and derived secretory vesicles.
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Affiliation(s)
- Rossana C N Melo
- Laboratory of Cellular Biology, Department of Biology, ICB, Federal University of Juiz de Fora, UFJF, Rua José Lourenço Kelmer, Juiz de Fora, Brazil.,Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
| | - Peter F Weller
- Laboratory of Cellular Biology, Department of Biology, ICB, Federal University of Juiz de Fora, UFJF, Rua José Lourenço Kelmer, Juiz de Fora, Brazil
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3
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Botan V, Dos Santos Borges TK, Rocha Alves ÉA, Claudino Pereira Couto S, Bender Kohnert Seidler H, Muniz-Junqueira MI. Enhanced activation of eosinophils in peripheral blood and implications for eosinophilic esophagitis diagnosis. J Gastroenterol Hepatol 2017; 32:1318-1327. [PMID: 28005266 DOI: 10.1111/jgh.13710] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 12/16/2016] [Accepted: 12/19/2016] [Indexed: 01/08/2023]
Abstract
BACKGROUND AND AIM Eosinophils are markers of the eosinophilic esophagitis (EoE) disease, and this work aimed to assess whether activation of eosinophils could be a noninvasive test to contribute for EoE diagnosis. METHODS The activation state of peripheral blood eosinophils in EoE patients and control subjects was assessed based on the morphological aspects of the eosinophil after adherence to slide. Cyclooxygenase-2 and 5-lipoxygenase expressions were evaluated by means of immunofluorescence microscopy to verify if and which eicosanoid pathway is triggered in eosinophils in blood in EoE. RESULTS The eosinophils of patients with EoE were significantly more activated than those of control individuals. The lowest percentage of normal eosinophils for control subjects was 40%, while the highest percentage of eosinophils of normal aspect for patients with EoE was 32%. Considering 36% as a cutoff for normal eosinophils, this value differentiated all individuals with EoE from individuals without the disease with a sensitivity of 100%, considering the diagnosis of EoE as currently defined. Eosinophils of EoE patients showed higher expression of cyclooxygenase-2 than those of control subjects. CONCLUSIONS The quantification of morphological changes in eosinophils is a feasible, easy, and reliable manner to identify EoE patients. Therefore, patients with symptoms of esophageal dysfunction showing higher than 36% activated eosinophils in peripheral blood could be a useful way to help definition and diagnostic criterion for EoE.
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Affiliation(s)
- Valéria Botan
- Laboratory of Cellular Immunology, Pathology, Faculty of Medicine, University of Brasília, Brasília, Distrito Federal, Brazil.,Alergya Clinic, Brasília, Distrito Federal, Brazil
| | - Tatiana Karla Dos Santos Borges
- Laboratory of Cellular Immunology, Pathology, Faculty of Medicine, University of Brasília, Brasília, Distrito Federal, Brazil
| | | | - Shirley Claudino Pereira Couto
- Laboratory of Cellular Immunology, Pathology, Faculty of Medicine, University of Brasília, Brasília, Distrito Federal, Brazil
| | - Heinrich Bender Kohnert Seidler
- Brasiliensis Laboratory, Brasília, Distrito Federal, Brazil.,Catholic University of Brasília, Brasília, Distrito Federal, Brazil
| | - Maria Imaculada Muniz-Junqueira
- Laboratory of Cellular Immunology, Pathology, Faculty of Medicine, University of Brasília, Brasília, Distrito Federal, Brazil
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Melo RCN, Weller PF. Vesicular trafficking of immune mediators in human eosinophils revealed by immunoelectron microscopy. Exp Cell Res 2016; 347:385-90. [PMID: 27562864 DOI: 10.1016/j.yexcr.2016.08.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Revised: 08/19/2016] [Accepted: 08/20/2016] [Indexed: 01/21/2023]
Abstract
Electron microscopy (EM)-based techniques are mostly responsible for our current view of cell morphology at the subcellular level and continue to play an essential role in biological research. In cells from the immune system, such as eosinophils, EM has helped to understand how cells package and release mediators involved in immune responses. Ultrastructural investigations of human eosinophils enabled visualization of secretory processes in detail and identification of a robust, vesicular trafficking essential for the secretion of immune mediators via a non-classical secretory pathway associated with secretory (specific) granules. This vesicular system is mainly organized as large tubular-vesicular carriers (Eosinophil Sombrero Vesicles - EoSVs) actively formed in response to cell activation and provides a sophisticated structural mechanism for delivery of granule-stored mediators. In this review, we highlight the application of EM techniques to recognize pools of immune mediators at vesicular compartments and to understand the complex secretory pathway within human eosinophils involved in inflammatory and allergic responses.
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Affiliation(s)
- Rossana C N Melo
- Laboratory of Cellular Biology, Department of Biology, ICB, Federal University of Juiz de Fora, UFJF, Rua José Lourenço Kelmer, Juiz de Fora, MG 36036-900, Brazil; Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, CLS 943, Boston, MA 02215, USA.
| | - Peter F Weller
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, CLS 943, Boston, MA 02215, USA
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Muniz-Junqueira MI, Barbosa-Marques SM, Junqueira LF. Morphological changes in eosinophils are reliable markers of the severity of an acute asthma exacerbation in children. Allergy 2013; 68:911-20. [PMID: 23745834 DOI: 10.1111/all.12176] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/24/2013] [Indexed: 12/29/2022]
Abstract
BACKGROUND Early identification of the severity of asthma exacerbation would be helpful for the management of patients. We aimed to evaluate the correlation of morphological change in activated eosinophils and the severity of an asthma exacerbation. METHODS Blood was collected from 55 asthmatic children: 40 of whom were having an exacerbation, 15 symptom-free, and 15 healthy controls. The percentage of eosinophils with morphological changes (emission of single or multiple pseudopods, presence of cytoplasmic vacuoles, releasing a small, moderate, or large quantity of granules, spreading, eosinophil death, and presence of cluster of free eosinophil granules) was quantified after the adherence to a slide and compared using the Mann-Whitney test. The correlation between the severity of the asthma exacerbation and the percentage changed eosinophils was tested with Spearman's correlation. RESULTS The proportion of activated eosinophils was higher in asthmatic symptom-free children than in the control group, and acute asthma exacerbation produced an additional increase in eosinophil activation (P < 0.01). More significantly increased morphological changes were emissions of multiple pseudopods, presence of cytoplasmic vacuoles, spreading, and presence of a cluster of free eosinophil granules (P < 0.001). The following were correlated with the severity of an asthma exacerbation: ≥14% of eosinophils emitting single pseudopod, 8% emitting multiple pseudopods, 17% with vacuoles, 28% eosinophils releasing a large quantity of granules, and 66% of spread eosinophils. CONCLUSIONS Quantifying the morphological changes in eosinophils is a feasible, easy, and reliable manner to identify the severity of an asthma exacerbation and therefore might improve the clinical management of asthmatic children.
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Affiliation(s)
- M. I. Muniz-Junqueira
- Laboratory of Cellular Immunology, Pathology Area, Faculty of Medicine; University of Brasilia; Brasilia; Brazil
| | - S. M. Barbosa-Marques
- Laboratory of Cellular Immunology, Pathology Area, Faculty of Medicine; University of Brasilia; Brasilia; Brazil
| | - L. F. Junqueira
- Cardiovascular Laboratory, Clinical Medicine Area, Faculty of Medicine; University of Brasilia; Brasilia; Brazil
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6
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Melo RCN, Dvorak AM, Weller PF. Contributions of electron microscopy to understand secretion of immune mediators by human eosinophils. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2010; 16:653-60. [PMID: 20875166 PMCID: PMC3420811 DOI: 10.1017/s1431927610093864] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Mechanisms governing secretion of proteins underlie the biologic activities and functions of human eosinophils, leukocytes of the innate immune system, involved in allergic, inflammatory, and immunoregulatory responses. In response to varied stimuli, eosinophils are recruited from the circulation into inflammatory foci, where they modulate immune responses through the release of granule-derived products. Transmission electron microscopy (TEM) is the only technique that can clearly identify and distinguish between different modes of cell secretion. In this review, we highlight the advances in understanding mechanisms of eosinophil secretion, based on TEM findings, that have been made over the past years and that have provided unprecedented insights into the functional capabilities of these cells.
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Affiliation(s)
- Rossana C N Melo
- Laboratory of Cellular Biology, Department of Biology, Federal University of Juiz de Fora, UFJF, Juiz de Fora, MG, Brazil.
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Melo RC, Weller PF. Piecemeal degranulation in human eosinophils: a distinct secretion mechanism underlying inflammatory responses. Histol Histopathol 2010; 25:1341-54. [PMID: 20712018 PMCID: PMC3427618 DOI: 10.14670/hh-25.1341] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Secretion is a fundamental cell process underlying different physiological and pathological events. In cells from the human immune system such as eosinophils, secretion of mediators generally occurs by means of piecemeal degranulation, an unconventional secretory pathway characterized by vesicular transport of small packets of materials from the cytoplasmic secretory granules to the cell surface. During piecemeal degranulation in eosinophils, a distinct transport vesicle system, which includes large, pleiomorphic vesiculo-tubular carriers is mobilized and enables regulated release of granule-stored proteins such as cytokines and major basic protein. Piecemeal degranulation underlies distinct functions of eosinophils as effector and immunoregulatory cells. This review focuses on the structural and functional advances that have been made over the last years concerning the intracellular trafficking and secretion of eosinophil proteins by piecemeal degranulation during inflammatory responses.
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Affiliation(s)
- Rossana C.N. Melo
- Laboratory of Cellular Biology, Department of Biology, Federal University of Juiz de Fora, UFJF, Juiz de Fora, MG, Brazil
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Peter F. Weller
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
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Minai-Fleminger Y, Elishmereni M, Vita F, Soranzo MR, Mankuta D, Zabucchi G, Levi-Schaffer F. Ultrastructural evidence for human mast cell-eosinophil interactions in vitro. Cell Tissue Res 2010; 341:405-15. [PMID: 20686785 DOI: 10.1007/s00441-010-1010-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Accepted: 06/17/2010] [Indexed: 12/15/2022]
Abstract
We have hypothesized that mast cells (MC) and eosinophils (Eos), the main effectors of allergy, can form an effector unit. These cells co-exist in the inflamed tissues during the late and chronic stages of allergy and have been shown to be capable of influencing each other's survival and activity via soluble mediators. We have recently described couples of receptor-ligands that are expressed on either/both of these cells and that imply a physical interaction. In this study, we have investigated the existence of short-term (60 min) in vitro interactions between human peripheral blood Eos and cord-blood-derived MC by transmission electron microscopy. We have found that MC and Eos adhere to each other; the lipid body content and the granule morphology of co-cultured MC and Eos, respectively, are altered, and the level of Eos peroxidase (EPO) released by co-cultured Eos is elevated. Moreover, the transfer of EPO from Eos to MC and tryptase from MC to Eos has been observed. Our results thus indicate that, when co-cultured, MC and Eos show signs of physical contact and of reciprocal activation. This is the first in vitro evidence of functional physical interactions between human MC and Eos, interactions that might also occur in vivo during allergic diseases.
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Affiliation(s)
- Yael Minai-Fleminger
- Pharmacology & Experimental Therapeutics Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Ein Kerem, Jerusalem 91120, Israel
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Abstract
Major basic protein (MBP), the predominant cationic protein of human eosinophil specific granules, is stored within crystalloid cores of these granules. Secretion of MBP contributes to the immunopathogenesis of varied diseases. Prior electron microscopy (EM) of eosinophils in sites of inflammation noted losses of granule cores in the absence of granule exocytosis and suggested that eosinophil granule proteins might be released through piecemeal degranulation (PMD), a secretory process mediated by transport vesicles. Because release of eosinophil granule-derived MBP through PMD has not been studied, we evaluated secretion of this cationic protein by human eosinophils. Intracellular localizations of MBP were studied within nonstimulated and eotaxin-stimulated human eosinophils by both immunofluorescence and a pre-embedding immunonanogold EM method that enables optimal epitope preservation and antigen access to membrane microdomains. In parallel, quantification of transport vesicles was assessed in eosinophils from a patient with hypereosinophilic syndrome (HES). Our data demonstrate vesicular trafficking of MBP within eotaxin-stimulated eosinophils. Vesicular compartments, previously implicated in transport from granules to the plasma membrane, including large vesiculotubular carriers termed eosinophil sombrero vesicles (EoSVs), were found to contain MBP. These secretory compartments were significantly increased in numbers within HES eosinophils. Moreover, in addition to granule-stored MBP, even unstimulated eosinophils contained appreciable amounts of MBP within secretory vesicles, as evidenced by immunonanogold EM and immunofluorescent colocalizations of MBP and CD63. These data suggest that eosinophil MBP, with its multiple extracellular activities, can be mobilized from granules by PMD into secretory vesicles and both granule- and secretory vesicle-stored pools of MBP are available for agonist-elicited secretion of MBP from human eosinophils. The recognition of PMD as a secretory process to release MBP is important to understand the pathological basis of allergic and other eosinophil-associated inflammatory diseases.
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10
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Melo RCN, Dvorak AM, Weller PF. Electron tomography and immunonanogold electron microscopy for investigating intracellular trafficking and secretion in human eosinophils. J Cell Mol Med 2008; 12:1416-9. [PMID: 18410520 PMCID: PMC2562554 DOI: 10.1111/j.1582-4934.2008.00346.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Electron tomography (ET) has increasingly been used to understand the complexity of membrane systems and protein-trafficking events. By ET and immunonanogold electron microscopy, we recently defined a route for vesicular transport and release of granule-stored products from within activated human eosinophils, cells specialized in the secretion of numerous cytokines and other proteins during inflammatory responses. Here, we highlight these techniques as important tools to unveil a distinct eosinophil vesicular system and secretory pathway.
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Affiliation(s)
- Rossana C N Melo
- Laboratory of Cellular Biology, Department of Biology Federal University of Juiz de Fora, UFJF, Juiz de Fora, Minas Gerais, Brazil.
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Melo RCN, Spencer LA, Dvorak AM, Weller PF. Mechanisms of eosinophil secretion: large vesiculotubular carriers mediate transport and release of granule-derived cytokines and other proteins. J Leukoc Biol 2008; 83:229-36. [PMID: 17875811 PMCID: PMC2734949 DOI: 10.1189/jlb.0707503] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Eosinophils generate and store a battery of proteins, including classical cationic proteins, cytokines, chemokines, and growth factors. Rapid secretion of these active mediators by eosinophils is central to a range of inflammatory and immunoregulatory responses. Eosinophil products are packaged within a dominant population of cytoplasmic specific granules and generally secreted by piecemeal degranulation, a process mediated by transport vesicles. Large, pleiomorphic vesiculotubular carriers were identified recently as key players for moving eosinophil proteins from granules to the plasma membrane for extracellular release. During secretion, these specialized, morphologically distinct carriers, termed eosinophil sombrero vesicles, are actively formed and direct differential and rapid release of eosinophil proteins. This review highlights recent discoveries concerning the organization of the human eosinophil secretory pathway. These discoveries are defining a broader role for large vesiculotubular carriers in the intracellular trafficking and secretion of proteins, including selective receptor-mediated mobilization and transport of cytokines.
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Affiliation(s)
- Rossana C. N. Melo
- Laboratory of Cellular Biology, Department of Biology, Federal University of Juiz de Fora, MG, Brazil
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
| | - Lisa A. Spencer
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
| | - Ann M. Dvorak
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
| | - Peter F. Weller
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA
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Melo RCN, Sabban A, Weller PF. Leukocyte lipid bodies: inflammation-related organelles are rapidly detected by wet scanning electron microscopy. J Lipid Res 2006; 47:2589-94. [PMID: 16940552 DOI: 10.1194/jlr.d600028-jlr200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Leukocyte lipid bodies are dynamic, functionally active organelles with central roles in inflammation. Here, we report that leukocyte lipid bodies are facilely detected by a versatile, potent technique, termed wet scanning electron microscopy (SEM), which combines the rapid preparation of light microscopy with the resolution of SEM. Using as leukocyte models resting and agonist-stimulated human eosinophils, cells that generate prominent numbers of lipid bodies in inflammatory conditions, we demonstrated that lipid bodies can be rapidly imaged as bright, highly contrasted structures under wet SEM and scored by computerized image processing. Critical advantages of this approach are that it permits cell observation in a fully hydrated system and facilitates lipid preservation. These attributes are especially important because lipid bodies are degraded during routine dehydration processes. Moreover, this technology is advantageous over lipophilic fluorescent probes because it allows sustained detection of lipid bodies in contrast to short-lived fluorescent labeling of these organelles. The value of wet SEM in enabling rapid and large-scale lipid body imaging and scoring within leukocytes is particularly important because lipid bodies are organelles underlying the heightened functions of inflammatory cells. Wet SEM technology provides new approaches and opportunities for delineations of lipid bodies in inflammatory diseases, including allergic inflammation.
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Affiliation(s)
- Rossana C N Melo
- Laboratory of Cellular Biology, Department of Biology, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil
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