Phagocytosis Of Cell Debris Research Articles

The generation, activation, and polarization of monocyte-derived macrophages in human malignancies.

Macrophages are immune cells that originate from embryogenesis or from the differentiation of monocytes. They can adopt numerous phenotypes depending on their origin, tissue distribution and in response to different stimuli and tissue environment. Thus, in vivo, macrophages are endowed with a continuum of phenotypes that are rarely strictly pro-inflammatory or anti-inflammatory and exhibit a broad expression profile that sweeps over the whole polarization spectrum. Schematically, three main macrophage subpopulations coexist in human tissues: naïve macrophages also called M0, pro-inflammatory macrophages referred as M1 macrophages, and anti-inflammatory macrophages also known as M2 macrophages. Naïve macrophages display phagocytic functions, recognize pathogenic agents, and rapidly undergo polarization towards pro or anti-inflammatory macrophages to acquire their full panel of functions. Pro-inflammatory macrophages are widely involved in inflammatory response, during which they exert anti-microbial and anti-tumoral functions. By contrast, anti-inflammatory macrophages are implicated in the resolution of inflammation, the phagocytosis of cell debris and tissue reparation following injuries. Macrophages also play important deleterious or beneficial roles in the initiation and progression of different pathophysiological settings including solid and hematopoietic cancers. A better understanding of the molecular mechanisms involved in the generation, activation and polarization of macrophages is a prerequisite for the development of new therapeutic strategies to modulate macrophages functions in pathological situations.

Support vector machine assisted morphological characterisation of retinal microglia in mice modelled with multiple sclerosis and age‐matched controls

AbstractPurposeRetinal thinning is a pathological feature of Multiple Sclerosis (MS). The retina is an optically visible part of the central nervous system which, like the brain, contain microglia. Microglia are the resident immune cells which may dynamically move between the ramified, hyper‐ramified, activated, rod and amoeboid morphotypes, in response to normal aging or disease. This study sought to establish the differences in total and individual microglia morphotype densities between MS mice, induced by cuprizone (CPZ) treatment, and age‐matched controls (Ctrl).MethodsC57 mice were fed either standard chow for the Ctrl or chow mixed with 0.2%w/w CPZ for the MS‐model, for 4 months (4 m) until their sacrifice at 6 m or 28 m. All animals were enucleated, retinas were dissected which were then immunostained for microglia using iba‐1, flat mounted and imaged. Image processing, cell counting and morphotyping algorithms, consisting of support vector machines (SVM), were developed. The data were analysed non‐parametrically (n: 6mCPZ = 7; 6mCtrl = 15; 28mCPZ = 10; 28mCtrl = 7).ResultsThe SVM‐C had performance accuracies of 87.9–100% with AUC 0.99–1.00 for each morphotype. Although no significant difference of total retinal microglia density between each experimental group, old MS mice (28mCPZ) had more ramified (p < 0.05) and amoeboid (ns) cells in comparison to young MS mice (6mCPZ) and old Ctrl mice (28mCtrl). Young mice (6mCPZ and 6mCtrl) had significantly more rod microglia (p < 0.01) in comparison to old mice (28mCPZ and 28mCtrl). 28mCPZ had significantly fewer activated, hyper‐ramified and rod cells (p < 0.05) compared to 28mCtrl whilst the 6mCPZ and 6mCtrl had no significant differences.ConclusionsA lack of total retinal microglia density differences and distinctive morphotype density differences suggest that cells may shift between morphotypes rather than by cell proliferation. The trends of ramified and amoeboid microglia may suggest increased surveillance and phagocytosis of cell debris with aging and CPZ treatment. However, these functional characteristics were not investigated in this study.

A Role for Microglia in Retinal Development.

Microglia are the resident macrophages of the CNS. Though they are best known for their traditional macrophage activities, such as the phagocytosis of cell debris and inflammatory responses after injury, microglia also play an integral role in the normal development of the brain and spinal cord. For

Microglia and Aging: The Role of the TREM2-DAP12 and CX3CL1-CX3CR1 Axes.

Depending on the species, microglial cells represent 5–20% of glial cells in the adult brain. As the innate immune effector of the brain, microglia are involved in several functions: regulation of inflammation, synaptic connectivity, programmed cell death, wiring and circuitry formation, phagocytosis of cell debris, and synaptic pruning and sculpting of postnatal neural circuits. Moreover, microglia contribute to some neurodevelopmental disorders such as Nasu-Hakola disease (NHD), and to aged-associated neurodegenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and others. There is evidence that human and rodent microglia may become senescent. This event determines alterations in the microglia activation status, associated with a chronic inflammation phenotype and with the loss of neuroprotective functions that lead to a greater susceptibility to the neurodegenerative diseases of aging. In the central nervous system (CNS), Triggering Receptor Expressed on Myeloid Cells 2-DNAX activation protein 12 (TREM2-DAP12) is a signaling complex expressed exclusively in microglia. As a microglial surface receptor, TREM2 interacts with DAP12 to initiate signal transduction pathways that promote microglial cell activation, phagocytosis, and microglial cell survival. Defective TREM2-DAP12 functions play a central role in the pathogenesis of several diseases. The CX3CL1 (fractalkine)-CX3CR1 signaling represents the most important communication channel between neurons and microglia. The expression of CX3CL1 in neurons and of its receptor CX3CR1 in microglia determines a specific interaction, playing fundamental roles in the regulation of the maturation and function of these cells. Here, we review the role of the TREM2-DAP12 and CX3CL1-CX3CR1 axes in aged microglia and the involvement of these pathways in physiological CNS aging and in age-associated neurodegenerative diseases.

Apoptotic Cancer Cells Suppress 5-Lipoxygenase in Tumor-Associated Macrophages.

The enzyme 5-lipoxygenase (5-LO) is key in the synthesis of leukotrienes, which are potent proinflammatory lipid mediators involved in chronic inflammatory diseases including cancer. 5-LO is expressed in immune cells but also found in cancer cells. Although the role of 5-LO in tumor cells is beginning to emerge, with the notion that tumor-promoting functions are attributed to its products, the function of 5-LO in the tumor microenvironment remains unclear. To understand the role of 5-LO and its products in the tumor microenvironment, we analyzed its expression and function in tumor-associated macrophages (TAMs). TAMs were generated by coculturing primary human macrophages (MΦ) with human MCF-7 breast carcinoma cells, which caused cell death of cancer cells followed by phagocytosis of cell debris by MΦ. Expression and activity of 5-LO in TAMs were reduced upon coculture with cancer cells. Downregulation of 5-LO in TAMs required tumor cell death and the direct contact between MΦ and dying cancer cells via Mer tyrosine kinase. Subsequently, upregulation of proto-oncogene c-Myb in TAMs induced a stable transcriptional repression of 5-LO. Reduced 5-LO expression in TAMs was mechanistically coupled to an attenuated T cell recruitment. In primary TAMs from human and murine breast tumors, 5-LO expression was absent or low when compared with monocyte-derived MΦ. Our data reveal that 5-LO, which is required for leukotriene production and subsequent T cell recruitment, is downregulated in TAMs through Mer tyrosine kinase-dependent recognition of apoptotic cancer cells. Mechanistically, we noticed transcriptional repression of 5-LO by proto-oncogene c-Myb and conclude that loss of stromal 5-LO expression favors tumor progression.

Müller glia and phagocytosis of cell debris in retinal tissue.

Müller cells are the predominant glial cell type in the retina of vertebrates. They play a wide variety of roles in both the developing and the mature retina that have been widely reported in the literature. However, less attention has been paid to their role in phagocytosis of cell debris under physiological, pathological or experimental conditions. Müller glia have been shown to phagocytose apoptotic cell bodies originated during development of the visual system. They also engulf foreign molecules that are injected into the eye, cone outer segments and injured photoreceptors. Phagocytosis of photoreceptor cell debris in the light-damaged teleost retina is primarily carried out by Müller cells. Once the microglial cells become activated and migrate to the photoreceptor cell layer, the phagocytic activity of Müller cells progressively decreases, suggesting a possible mechanism of communication between Müller cells and neighbouring microglia and photoreceptors. Additionally, it has been shown that phagocytic Müller cells acquire proliferating activity in the damaged teleost retina, suggesting that engulfment of apoptotic photoreceptor debris might stimulate the Müller glia to proliferate during the regenerative response. These findings highlight Müller glia phagocytosis as an underlying mechanism contributing to degeneration and regeneration under pathological conditions.

Potential Drugs Targeting Microglia: Current Knowledge and Future Prospects

Inflammation in the central nervous system (CNS) may occur as a result of trauma, infection or neurodegenerative stimuli and is characterized by activation of microglia, the resident immune cells of the CNS. Activated microglia proliferate rapidly, migrate to the site of injury or infection and elicit immune response by phagocytosis of cell debris, production of cytokines, chemokines and reactive oxygen species, and presentation of antigens to other immune cells. In addition, microglia participate in tissue repair by producing neurotrophic factors. However, when microglia are chronically activated, they become neurotoxic to the surrounding CNS parenchyma. Chronic activation of microglia has been shown to augment neurodegeneration in Parkinson's disease (PD), Alzheimer's disease (AD), brain injury and number of other CNS pathologies. Identification of factors that control microglial activation, therefore, has become the major focus of recent research. A number of herbal and chemical compounds have been shown to attenuate microglial activation. However, these compounds exhibit non-specificity and produce unpleasant side-effects. Here, we provide a comprehensive review on some of the currently available drugs known to reduce microglial activation, their molecular targets and the subcellular signaling networks on which they act. We also review some of the newly emerging therapeutic avenues such as 'epidrugs' and finally emphasize on the importance of targeted drug delivery systems for alleviating microglia-mediated neurotoxicity.

Immunohistochemical study of arginase-1 in the spinal cords of Lewis rats with experimental autoimmune encephalomyelitis

Arginase-1, a marker for M2 phenotype alternatively activated macrophages, inhibits inflammation and is associated with phagocytosis of cell debris and apoptotic cells. We analyzed the expression of arginase-1, a competitive enzyme of inducible nitric oxide synthase (iNOS), in the spinal cords of Lewis rats with experimental autoimmune encephalomyelitis (EAE). Western blot analysis showed that both arginase-1 and iNOS significantly increased in the spinal cords of rats at the peak stage of EAE compared with the expression level in control animals (p<0.05) and declined thereafter. Immunofluorescent staining demonstrated that increased expression of arginase-1 in EAE spinal cords was confirmed in macrophages as well as in some neurons and astrocytes that were constitutively positive for arginase-1 in normal spinal cords. A semiquantitative analysis by immunofluorescence showed that in EAE lesions, an increased level of arginase-1 immunoreactivity was matched with ED1-positive macrophages, which were also positive for activin A, a marker for the M2 phenotype. Taking all of these findings into consideration, we postulate that the increased level of arginase-1, which is partly from M2 macrophages, contributes to the modulation of neuroinflammation in EAE lesions, possibly through the reduction of nitric oxide in the lesion via competition with iNOS for the use of l-arginine.

Agent-based model of macrophage action on endocrine pancreas

This paper proposes an agent-based model of the action of macrophages on the beta cells of the endocrine pancreas. The aim of this model is to simulate the processes of beta cell proliferation and apoptosis and also the process of phagocytosis of cell debris by macrophages, all of which are related to the onset of the autoimmune response in type 1 diabetes. We have used data from the scientific literature to design the model. The results show that the model obtains good approximations to real processes and could be used to shed light on some open questions concerning such processes.

Spontaneous Histiocytic Sarcoma of the Popliteal Lymph Node in a Young Sprague-Dawley Rat

The present report describes a rare case of spontaneous primary histiocytic sarcoma of the popliteal lymph node in a 19-week-old female Sprague-Dawley (SD) rat. At necropsy, a 10 mm-diameter whitish nodule was found at the site of the femoral muscle in the right hindlimb. Histopathologically, the nodule comprised large pleomorphic histiocyte-like cells with abundant eosinophilic or foamy cytoplasm. Multinucleated giant cells, necrotic foci surrounded by palisading arrays of epithelioid histiocyte-like cells and phagocytosis of cell debris or erythrocytes by the neoplastic cells were occasionally observed. Invasion of the tumor cells into the surrounding adipose tissue was found focally, but there were no distal metastases. Immunohistochemically, the neoplastic cells were positive for vimentin, CD68 (ED1) and lysozyme. We concluded that this tumor occurred in the popliteal lymph node, considering the anatomical location of the lesion and the presence of the remnants of lymphoid tissue involved in the tumor.

First Record of Hemocytes and Oenocytes in Freshwater Ostracodes

This study provides morphological descriptions of three distinct types of hemocytes and one type of oenocyte newly observed in the body cavity of several freshwater ostracode species (Candona candida, C. neglecta, Herpetocypris reptans, H. incongruens, Eucypris virens, Psychrodromus olivaceus, Notodromas monacha, N. persica and Scottia birigida, all Podocopida, Cypridoidea). These cells were found in both males and females and in both juveniles and adults predominantly in inter-lamellar space, along the dorsal margin of the body cavity and in the anteroventral part of the body cavity. In TEM, large granulocytes with a number of pseudopodia and remarkable rounded granula were observed. Their affinity to muscle syncytia and a role in phagocytosis of exogenous particles is distinct. Oenocytoid-like cells with homogenous cytoplasm, rich in polyribosomes and with few membrane-delimited vesicles, were caught in the peripheral parts of body cavity accumulating in special multicellular formations. The oenocytoid-like cells were observed in two cases also by light microscopy. Two types of plasmatocytes (agranular and granular) with numerous pseudopodia were observed in TEM to be involved in phagocytosis of cell debris. Moreover, the plasmatocytes are located in close vicinity with the multicellular formations of oenocytoid-like cells and envelope them or form a sheath. Oenocytes were shown by light microscopy using histological staining to occur in huge amounts in juveniles. In adults their frequency becomes considerably lower. Possible functions of these cells are discussed in the context of invertebrate haematology, physiology and immunology.

In vitro model of microglial deramification: ramified microglia transform into amoeboid phagocytes following addition of brain cell membranes to microglia-astrocyte cocultures.

Changes in the morphology of ramified microglia are a common feature in brain pathology and culminate in the appearance of small, rounded, microglia-derived phagocytes in the presence of neural debris. Here, we explored the effect of adding brain cell membranes on the morphology of alphaMbeta2-integrin (CD11b/CD18, CR3) positive microglia cultured on a confluent astrocyte substrate as an in vitro model of deramification. Addition of brain membranes led to a loss of microglial ramification, with full transformation to small, rounded, macrophages at 20-40 microg/ml. Time course studies showed a rapid response, with first effects at 1-3 hours, and full transformation at 24-48 hours. Removal of cell membranes and exchange of the culture medium led to a similarly rapid process of reramification. Comparison of cell membranes from different tissues at 20 microg/ml showed strong transforming effect for the brain, more moderate for kidney and liver, and very weak for spleen and skeletal muscle. Fluorescent labeling of brain membranes revealed uptake by almost all rounded macrophages, by a subpopulation of glial fibrillary acidic protein (GFAP)-positive astrocytes, but not by ramified microglia. Phagocytosis of inert fluorobeads did not lead to a transformation into macrophages but their phagocytosis was inhibited by brain membranes, pointing to a saturable uptake mechanism. In summary, addition of brain cell membranes and their phagocytosis leads to a rapid and reversible loss of ramification. The differences in transforming activity from different tissues and the absence of effect from phagocytosed fluorobeads suggest, however, the need for a second stimulus following the phagocytosis of cell debris.

Polyglobuly versus polycythemia vera

Differentiation of an elevated hemoglobin/hematocrit level warrants not only the determination of relevant laboratory values, including erythropoietin, but also an elaborate evaluation of bone marrow histopathology. Particularly in the initial stages of polycythemia vera (PV), when not all stringent clinical criteria are completely fulfilled, a more refined analysis of morphological features helps to distinguish autonomous (PV) from spurious or secondary erythrocytosis - polyglobuly (PG). PV is characterized by a panmyelosis, i.e., a trilinear proliferation of all cell lineages, whereas in PG erythropoiesis predominates. Megakaryopoiesis exerts a significant impact on differentiation, because in PV there is a conspicuous grouping associated with a strikingly expressed pleomorphous appearance. This peculiar feature implicates assemblies of small- to medium-sized megakaryocytes lying adjacent to giant cells with extensively lobulated, staghorn-like nuclei. A further discriminating parameter is presented by the interstitial lesions frequently occurring in PG. These, according to the usually underlying inflammatory cause (chronic bronchitis-recurrent bronchopneumonias), include iron-laden macrophages, a prominent perivascular plasmacytosis, phagocytosis of cell debris by histiocytic reticular cells and often an in- crease in the number of eosinophils. Comparable findings are not, or only to a minor ex-tent, detectable in PV. In conclusion, by regarding hematopoiesis and the myeloid stroma initial stages of PV may be definitively distinguished from PG.

Polymorphonuclear Leukocytes in the Fetal Membranes are Activated in Patients with Preterm Delivery: Ultrastructural and Enzyme-histochemical Evidence

The purpose of this study was to examine evidence for the presence of activated leukocytes in the fetal membranes from patients with preterm delivery. Polymorphonuclear leukocytes in fetal membranes from seven patients with preterm delivery (26–32 weeks of gestation) were analysed using transmission electron microscopy and ultrastructural enzyme-histochemistry for peroxidase and alkaline phosphatase. A large number of leukocytes accumulated in the fetal membranes from preterm deliveries. Phagosome, phagocytosis of cell debris, attachment of primary granules to the phagosomal membrane and cell surface projections were observed in fetal membrane leukocytes from preterm delivery but not in peripheral blood leukocytes. Peroxidase and alkaline phosphatase activity was demonstrated on the plasma membrane of the phagosomes.Morphological and enzyme-histochemical observation indicated that polymorphonuclear leukocytes in the fetal membrane in patients with preterm delivery were stimulated or activated. Such activated leukocytes may play a role in the pathophysiology or pathogenesis of preterm delivery.

Link between optic nerve regrowth failure and macrophage stimulation in mammals

The adult mammalian central nervous system (CNS) fails to regenerate its axons following injury. A comparison between its postinjury response and that of axons of nervous systems capable of regeneration reveals major differences with respect to inflammation. In regenerative systems, a large number of macrophages rapidly invade the injured site during the first few hours and days after the injury. Following their activation/differentiation through interaction with the host tissue, they play a central role in tissue healing through phagocytosis of cell debris and communication with cellular and molecular elements of the damaged tissue. Relative to the peripheral nervous system (PNS), macrophage recruitment in the adult mammalian CNS is delayed and is restricted in amount and activity. It was recently proposed that in injured mammalian CNS tissue, implantation of macrophages stimulated by prior co-culture with segments of peripheral (sciatic) nerves can compensate, at least in part, of the restricted postinjury inflammatory reaction. In the present study, this experimental paradigm is further explored and shows that there is no conflict between the systemic use of anti-inflammatory compounds and treatment with stimulated macrophages to promote regrowth of neuronal tissue.

Diabetes manifestation in BB rats is preceded by pan-pancreatic presence of activated inflammatory macrophages.

Pancreata of normoglycemic diabetes-prone (dp) and diabetes-resistant (dr) BB rats and normal Wistar rats were screened for macrophage infiltration by immunohistochemistry and by electron microscopy. Inflammatory macrophages were found in the endocrine as well as the exocrine part of the pancreata from dp BB rats. In the exocrine tissue they had a different phenotype (ED1+, ED2+, W3/25+, Ox17+) from that found in pancreata from dr BB and Wistar rats (predominantly ED1-, ED2+, W3/25+, Ox17-). The number of macrophages in exocrine portions of pancreata from the various rat strains were not different. By electron microscopy scattered macrophage-associated tissue lesions and phagocytosis of cell debris were found throughout the exocrine tissue and in islets of dp BB rats. Such lesions were low or absent in biopsies of animals that later did not develop diabetes. We conclude that macrophage-mediated cytotoxicity during the early phases of diabetes development in BB rats is not restricted to islets, but is a generalized, pan-pancreatic event.

Morphologic effects of mitoxantrone and a related anthracenedione on lymphoid tissues

A single non-toxic dose of mitoxantrone or a related anthraquinone derivative caused extensive destruction of splenic marginal zone cells in rats and mice. This was followed by phagocytosis of cell debris and long-lasting atrophy. Germinal centers of splenic follicles were also affected. Small doses gave a cumulative effect and tolerance did not develop. Regional draining (but not distant) lymph nodes also had lymphocytic necrosis. The localization of the lymphocytolysis in the spleen may be related to the open circulation of blood in the marginal zone, and to the distribution of B-lymphocytes or B-lymphocyte subsets.

Processing of cell debris suggestive of phagocytosis in the follicular cavities of the avian adenohypophysis

The effects of the administration of the biogenic amine precursors L-DOPA and 5-hydroxy-L-tryptophan on the ultrastructure of the nongranulated, folliculo-stellate cells of the avian adenohypophysis were investigated in an attempt to approach the function of these cells. The analysis of the ultrastructural changes induced by these compounds revealed that the folliculo-stellate cells can encircle large portions of granulated, hormonogenic cells and, subsequently, phagocytize them. After 5-hydroxy-L-tryptophan treatment, junctional complexes appeared between non-granulated and granulated cells. Moreover, a remarkable dark cytoplasm containing autophagic vacuoles was found in some folliculo-stellate cells. In view of the literature, the observations reported here argue in favour of a role in phagocytosis of cell debris and/or of surplus of secretory material, as a result of endocrine dysfunctioning. Nevertheless, the capability of transformation of hormone-producing cells into folliculo-stellate cells has to be considered.

Phagocytosis and resorption during the reassembly of dissociated embryonic cells of sea urchins.

Time-lapse and electron microscopic observations were made on both epithelial and mesenchymal cells during the reassembly of embryos from dissociated cells of Strongylocentrotus purpuratus. In epithelial cells, where lysosomes are produced through the fusion of saccules formed from Golgi bodies, both phagocytosis of cell debris and resorption of differentiated cell structures were observed. In these cells, the lysosomes migrate and fuse with both autosomes and phagosomes. On the other hand, in the mesenchyme cells, where lysosomes are produced through the direct enlargement of the Golgi body's cisterna, neither phagocytosis nor resorption was observed. The migration of the lysosomes to the epithelial cell margins is the first indication of a re-establishment of cellular polarity after dissociation.

Cell death in developing skeletal muscle: histochemistry and ultrastructure.

The histological, histochemical and ultrastructural features of cell death in the normal human foetus are described. The age range of the foetuses was 7 to 16 wk. Cell death was observed in all foetuses between 10 and 16 wk. On the basis of these findings it is suggested that disintegration of cell membrane may be a crucial factor in this process. Acid phosphatase activity and phagocytosis of cell debris are evidently not the main means of disposal of degenerate cell products. The possible relevance of cell death in embryogenesis for dystrophic processes is discussed.