The macrophage

Macrophage-driven nutrient delivery to phagosomal Staphylococcus aureus supports bacterial growth

Staphylococcus aureus is a notorious pathogen causing significant morbidity and mortality worldwide. The ability of S. aureus to survive and replicate within phagocytes such as macrophages represents an important facet of immune evasion and contributes to pathogenesis. The mechanisms by which S. aureus acquires nutrients within host cells to support growth remain poorly characterized. Here, we demonstrate that macrophages infected with S. aureus maintain their dynamic ruffling behavior and consume macromolecules from the extracellular milieu. To support the notion that fluid-phase uptake by macrophages can provide S. aureus with nutrients, we utilized the pharmacological inhibitors PIK-III and Dynasore to impair uptake of extracellular macromolecules. Inhibitor treatment also impaired S. aureus replication within macrophages. Finally, using a mutant of S. aureus that is defective in purine biosynthesis we show that intracellular growth is inhibited unless the macrophage culture medium is supplemented with the metabolite inosine monophosphate. This growth rescue can be impaired by inhibition of fluid-phase uptake. In summary, through consumption of the extracellular environment macrophages deliver nutrients to phagolysosomal S. aureus to promote bacterial growth.

The outcome of phagocytic cell division with infectious cargo depends on single phagosome formation

Given that macrophages can proliferate and that certain microbes survive inside phagocytic cells, the question arises as to the post-mitotic distribution of microbial cargo. Using macrophage-like cells we evaluated the post-mitotic distribution of intracellular Cryptococcus yeasts and polystyrene beads by comparing experimental data to a stochastic model. For beads, the post-mitotic distribution was that expected from chance alone. However, for yeast cells the post-mitotic distribution was unequal, implying preferential sorting to one daughter cell. This mechanism for unequal distribution was phagosomal fusion, which effectively reduced the intracellular particle number. Hence, post-mitotic intracellular particle distribution is stochastic, unless microbial and/or host factors promote unequal distribution into daughter cells. In our system unequal cargo distribution appeared to benefit the microbe by promoting host cell exocytosis. Post-mitotic infectious cargo distribution is a new parameter to consider in the study of intracellular pathogens since it could potentially define the outcome of phagocytic-microbial interactions.

Effect of macrophage differentiation and exposure to mildly oxidized LDL on the proteolytic repertoire of THP-1 monocytes

Lipid-laden monocyte/macrophages in atherosclerotic plaques can produce a range of proteinases capable of degrading components of the plaque extracellular matrix, an event that may weaken plaques, rendering them vulnerable to rupture. The effects of differentiation from monocytes to macrophages and exposure to mildly oxidized LDL (Ox-LDL) on the expression of a range of proteinases and their inhibitors were assessed in the human THP-1 cell line. Of 56 proteinases/inhibitors investigated, 17 were upregulated during macrophage differentiation, including several matrix metalloproteinases (MMPs) and cathepsins along with their native inhibitors. Similarly, expression of matrix-degrading proteinases was also increased during differentiation of human primary macrophages. In conjunction, the proteolytic capacity of the cells increased, as assessed by substrate zymography. Subsequent exposure of differentiated THP-1 cells to mildly Ox-LDL increased the expression of a control gene (adipocyte lipid binding protein) and increased the activity of nuclear factor-kappaB and activator protein-1 in serum-free conditions but did not significantly affect the expression of any of the proteinases or inhibitors investigated. These results indicate that in this model macrophage differentiation, rather than exposure to Ox-LDL, has a more important effect on the expression of genes involved in extracellular matrix remodeling.

Ultrastructural, immunocytochemical and flow cytometry study of mouse peritoneal cells stimulated with carrageenan

In the present paper we performed a morphological characterization of mouse peritoneal cells stimulated in vivo for 24 h with carrageenan (CAR) and lipopolysaccharide (LPS) by ultrastructural and flow cytometry analysis. In all samples, the flow cytometry studies showed the presence of three major populations consisting of monocytes, macrophages and lymphocytes. A special recruitment of monocytes was detected in CAR-injected mice. Macrophages and monocytes from CAR-treated mice displayed a characteristic phenotype, with a larger number of cytoplasmic vacuoles and numerous membrane projections, as compared to the cells collected from LPS- and PBS-injected mice. The induction of vacuolization was also confirmed upon in vitro treatment with CAR for 15 min to 24 h. The in vivo CAR-induced vacuoles were not related to lipid storage as judged by the lack of lipidic labeling after imidazole treatment at the ultrastructural level. In order to investigate the acidic nature of the vacuoles we used acidothropic probes, Lysotracker Yellow (LY) and Acridine Orange (AO). CAR injection activated the ability of peritoneal cells to incorporate LY around 2-5 times higher than control cells. However, the AO incorporation was 10-fold lower in CAR-stimulated cells than in LPS-stimulated ones. It is possible that the increase in intracellular vacuolization observed in CAR-stimulated cells could be related to exocytosis, since in most vacuoles the inflammatory protein MRP-14 was immunolocalized. The presence of MRP-14 in the culture supernatant of adherent peritoneal cells from CAR-injected mice was further comfirmed by ELISA, suggesting the discharge of MRP-14 enriched vacuole contents in the extracellular medium. We concluded that the morphological characteristics of activated monocytes and macrophages may depend on the nature of the triggering stimuli. Our observations reflect different functional phenotypes of monocytes/macrophages after in vivo stimulation with inflammatory agents such as CAR and LPS.

Subpopulations of mouse resident peritoneal macrophages fractionated on Percoll gradients show differences in cell size, lectin binding and antigen expression suggestive of different stages of maturation

Aiming the identification of macrophage heterogeneity, mouse resident peritoneal cells were fractionated on discontinuous Percoll gradients into six discrete fractions (0, 1, 2, 3, 4 and 5 in order of increasing density). All six fractions and the total population were characterized by light and electron microscopy, and flow cytometry. The least dense fraction (0) had a low viability (44%); fractions 4 and 5 had a low percentage of macrophages. Light microscopy and flow cytometry of macrophage-enriched fractions 1, 2 and 3 showed an inverse correlation between diameter and cell density, as well as suitable differences in lectin binding to the macrophages of each fraction. The surface of macrophages from fraction 1 had more sialyl residues (higher binding of the lectin LFA), less galactosyl residues (lower binding of the lectin PNA) and expressed more receptors for the antibodies M1/70 (Mac-1) and F4/80; fraction 3 had an opposite binding behavior for the lectins and expressed fewer receptors for both antibodies; fraction 2 had an intermediate behavior for both parameters. Binding of the lectins Con A and HPA showed slight differences, whereas UEA I did not present a detectable difference among the fractions analyzed. These findings suggest that the macrophage heterogeneity achieved by the gradient separation of resident peritoneal cells could be explained by different stages of macrophage maturation.

The paradox of Ferrata and the fate of the extruded red cell nucleus: two problems concerning erythropoiesis in the human

A critical analysis of the present erythropoietic pathway reveals two problems which require resolving. One is the paradox of the basophilic erythroblast, and the other is the fate of the extruded red cell nucleus. The problems can be overcome if erythropoiesis is looked at differently, and the orthochromatic normoblast considered to arise directly from a denuded stem cell nucleus as has been previously suggested. The orthochromatic normoblast extrudes its nucleus leaving behind a reticulocyte. The extruded but functionally impaired nucleus of the orthochromatic normoblast then gives rise to a polychromatic normoblast, a defective cell. The poorly made cytoplasm of the polychromatic normoblast is shed and its nucleus, now non-functional, undergoes complete dissolution into an aggregate of ultrafine particles. The theory has the advantage that the fate of the extruded red cell nucleus can be explained without having to introduce phagocytosis by macrophages and all the immunological difficulties which this entails. The new pathway does away with the basophilic erythroblast as a haemoglobin-producing cell, and it is argued that the cell instead is a ferritin storage cell, and that erythropoiesis is the result of two separate but interdependent pathways, a ferritin storage pathway and a haemoglobin production pathway. Evidence is put forward to support the new pathways.

Zanvil Alexander Cohn 1926-1993

Zanvil Alexander Cohn, an editor of this Journal since 1973, died suddenly on June 28, 1993. Cohn is best known as the father of the current era of macrophage biology. Many of his scientific accomplishments are recounted here, beginning with seminal studies on the granules of phagocytes that were performed with his close colleague and former editor of this Journal, James Hirsch. Cohn and Hirsch identified the granules as lysosomes that discharged their contents of digestive enzymes into vacuoles containing phagocytosed microbes. These findings were part of the formative era of cell biology and initiated the modern study of endocytosis and cell-mediated resistance to infection. Cohn further explored the endocytic apparatus in pioneering studies of the mouse peritoneal macrophage in culture. He described vesicular inputs from the cell surface and Golgi apparatus and documented the thoroughness of substrate digestion within lysosomal vacuoles that would only permit the egress of monosaccharides and amino acids. These discoveries created a vigorous environment for graduate students, postdoctoral fellows, and junior and visiting faculty. Some of the major findings that emerged from Cohn's collaborations included the radioiodination of the plasma membrane for studies of composition and turnover; membrane recycling during endocytosis; the origin of the mononuclear phagocyte system in situ; the discovery of the dendritic cell system of antigen-presenting cells; the macrophage as a secretory cell, including the release of proteases and large amounts of prostaglandins and leukotrienes; several defined parameters of macrophage activation, especially the ability of T cell-derived lymphokines to enhance killing of tumor cells and intracellular protozoa; the granule discharge mechanism whereby cytotoxic lymphocytes release the pore-forming protein perforin; the signaling of macrophages via myristoylated substrates of protein kinase C; and a tissue culture model in which monocytes emigrate across tight endothelial junctions. In 1983, Cohn turned to a long-standing goal of exploring host resistance directly in humans. He studied leprosy, focusing on the disease site, the parasitized macrophages of the skin. He injected recombinant lymphokines into the skin and found that these molecules elicited several cell-mediated responses. Seeing this potential to enhance host defense in patients, Cohn was extending his clinical studies to AIDS and tuberculosis. Zanvil Cohn was a consummate physician-scientist who nurtured the relationship between cell biology and infectious disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokine-induced differentiation of cultured nonadherent macrophages

Monocytes were isolated from peripheral blood and cultured in vitro for more than 3 weeks in glass chamber slides. Phenotypically and ultrastructurally these nonadherent macrophages (NAM) appear similar to connective tissue resident macrophages. They constitutively secrete a high amount of IL-1ra and little or no IL-1 alpha or IL-1 beta. When exposed to GM-CSF, IL-2, or IFN-gamma for 24 hr, NAM become adherent and undergo dramatic morphological changes. Cytokines treatment primes NAM for increased LPS-mediated TNF production and these GM-CSF- and LPS-treated NAM are cytotoxic to WEHI 164, a TNF-sensitive target. Morphological changes and TNF production are both inhibited by antimetabolites and a variety of antineoplastic drugs. Although morphology inhibition is reversible under certain circumstances, inhibition of TNF synthesis is irreversible. These findings suggest that cytokines might play a role in differentiation and maturation of long-term cultured monocytes. Furthermore, the effects of antimetabolites and antineoplastic drugs on arresting the differentiation processes may significantly impair antitumor functions of macrophages.

Differential expression of the platelet-derived growth factor-A and -B genes during maturation of monocytes to macrophages

1. Regulation of platelet-derived growth factor (PDGF)-A and -B gene expression was studied using resting monocytes, in vitro matured monocytes and alveolar macrophages. 2. Resting monocytes constitutively transcribed both PDGF-A and -B genes. When monocytes matured to macrophages in vitro, the transcription rates of both genes increased markedly. 3. Consistent with the transcription rates, resting monocytes constitutively expressed both PDGF-A and -B mRNAs. Interestingly, the PDGF-B mRNA levels increased markedly after the maturation, whereas the PDGF-A mRNA did not change. 4. Alveolar macrophages constitutively transcribed both PDGF-A and -B genes at almost the same rates. However, these cells contained 5-fold more PDGF-B mRNA than PDGF-A mRNA. 5. Immunohistochemical study using anti-PDGF-AA and anti-PDGF-BB antibodies suggested that PDGF-BB homodimers were more abundant than -AA homodimers or -AB heterodimers in alveolar macrophages and in vitro matured monocytes. 6. Together these observations indicate that in vitro matured monocytes and alveolar macrophages preferentially express PDGF-B mRNA and produce PDGF-BB homodimers, despite the equal transcription rates for both PDGF-A and -B genes.

Evidence for an altered lipid metabolic state in circulating blood monocytes under conditions of hyperlipemia in swine and its implications in arterial lipid metabolism

Circulating blood monocytes were isolated from normal and hypercholesterolemic swine, and the monocyte lipid compositions and lipid biosynthesis profiles were assessed. The data indicate that monocytes freshly isolated from hyperlipemic swine have increased phospholipid and cholesterol contents and have increased biosynthetic capability for synthesizing phospholipids, triglycerides, and cholesteryl esters, but not cholesterol. The profile of the stimulated lipid synthesis capability is similar to that of the swine aortic intima undergoing atherogenic change. These studies indicate that circulating blood monocytes in hyperlipemic swine, which are known to give rise to intimal foam cells in the early fatty streak lesion, can contribute to altered vessel lipid metabolism without a requirement for in situ modification by wall factors.

Analysis of the monocyte chemotactic response to lysophosphatidylcholine: role of lysophospholipase C

Previously, we reported that lysophosphatidylcholine (lyso-PtdCho), a component of oxidized low-density lipoprotein, was a monocyte chemoattractant (M.T. Quinn et al. (1988) Proc. Natl. Acad. Sci. USA 85, 2805-2809). Monocyte chemotaxis was also stimulated by lyso-platelet activating factor but not by platelet activating factor itself. In the present studies, we used other analogs of lyso-PtdCho to determine structural and metabolic features required for chemotactic activity. Although both D- and L-lyso-PtdCho stimulated chemotaxis, suggesting a lack of stereospecificity, studies using propanediol and ethanediol analogs of lyso-PtdCho suggested that a free hydroxyl moiety or an ester-linked fatty acid vicinal to the phosphocholine group of the lysophospholipid was required for the expression of activity. Incubation of [3H]choline-labeled lyso-PtdCho with monocytes resulted in the formation of labeled PtdCho, glycerophosphocholine (GPC), phosphocholine, and free choline, while resident peritoneal macrophages, cells which we show do not respond chemotactically to lyso-PtdCho, metabolized the labeled substrate to generate only labeled PtdCho and GPC; no labeled phosphocholine was found, suggesting a possible role for lysophospholipase C activity in the monocyte chemotactic response. Although monoacylglycerol, the product of lysophospholipase C hydrolysis of lyso-PtdCho, was not chemotactic for monocytes, diacylglycerol demonstrated chemotactic activity, suggesting that the subsequent acylation to diacylglycerol may be involved in the monocyte chemotactic response to lyso-PtdCho. Indeed, monocytes incorporated [3H]glycerol from [3H]glycerol-labeled lyso-PtdCho into di- and triacylglycerol. Based on these results, a model is proposed whereby the monocyte chemotactic response to lyso-PtdCho involves a sequence of metabolic steps which includes hydrolysis of lyso-PtdCho to monoacylglycerol and phosphocholine by lysophospholipase C followed by acylation of monoacylglycerol to diacylglycerol. Diacylglycerol would then act as an intracellular second messenger that could activate or facilitate the chemotactic response.

Time course of wound healing

Wound healing is a special kind of inflammation. Undisturbed wound healing is subject to a fixed time schedule of biochemical and cellular events. It is virtually impossible to deal with the time course of wound healing without describing the cellular and non-cellular events involved. The activity and mode of cell action after injury are coordinated by spatial and chronological factors, as well as by different mediators and cell-cell interacting signals. During wound healing the sequence of different signals and message substances, such as mediators of inflammation, fulfill a key function in wound repair. The report describes the time course of healing and the control of cellular events by different mediators and cell interactions. Emphasis is placed on temporal aspects, including the various signals leading to typical cellular events in wound healing.

Lipopolysaccharide enhances monocyte adherence to matrix-bound fibronectin

Fibronectin (Fn), an extracellular matrix glycoprotein with binding sites for collagen, fibrin, heparin, and cell surfaces, is a nonimmune opsonin which up-regulates phagocytic function and facilitates adherence of human monocytes. We have developed a simple assay to study adherence of peripheral blood monocytes to Fn on a gelatin matrix. While cell adherence was enhanced by the presence of Fn in a dose-dependent manner, it was inhibited by peptides containing the Arg-Gly-Asp (RGD) cell attachment sequence or by coating the matrix with antibodies directed against Fn. Preincubation of monocytes for 30 min with Escherichia coli lipopolysaccharide (LPS) at doses of 1-50 micrograms/ml increased adherence to Fn-gelatin but not to gelatin alone, while longer preincubation (24 hr) resulted in similar changes at lower doses (0.01-1.0 micrograms/ml). Enhanced Fn adherence may be essential for monocyte localization to sites of inflammation.

Lysosomal hydrolases of human vascular cells: response to agonists of endothelial function

Endothelial injury has been proposed as a feature of a wide variety of vascular diseases, and release of endothelial lysosomal hydrolases could contribute to the pathological changes seen. We have determined the relative activities of 14 glycosidases, two esterases and four peptide hydrolases in human umbilical vein endothelial cells and investigated whether known agonists of endothelial function, or materials known to modulate hydrolase secretion in other phagocytic cells, influenced the activity or secretion of these enzymes by human umbilical vein endothelial cells. Hexosaminidase, beta-galactosidase, beta-glucuronidase and alpha-iduronidase accounted for most of the measured glycosidase activity. Acid phosphatase activity greatly exceeded arylsulphatase activity, and most of the measured peptidase activity was due to acid peptidases. Optimum pH and apparent Km values were determined for the most abundant hydrolases. Exposure of human umbilical vein endothelial cells to bradykinin, thrombin or interleukin-1 resulted in negligible release of either hexosaminidase or lactate dehydrogenase (LDH), in contrast to phorbol myristate acetate, which caused a parallel, dose-dependent release of both enzymes. Treatment of these cells with calcium ionophore A23187, trypsin or platelet-activating factor, caused less than 10% release of either hexosaminidase or LDH. Agents known to modulate lysosomal enzyme secretion by other phagocytic cells failed to induce selective secretion of lysosomal enzymes by human umbilical vein endothelial cells.

Localization of thyroid hormone in subpopulations of rat alveolar macrophages

Radioimmunoassay and immunocytochemical staining methods were used to study the distribution of thyroid hormone in rat alveolar macrophages. The cells were fractionated into six subpopulations by Percoll density gradient. Positive immunoreactive tri-iodothyronine (T3) was observed in all subpopulations of macrophages, especially in low-density (1.040 and 1.050 g cm-3) groups, by avidin-biotin-peroxidase immunostaining techniques. The macrophages also showed various patterns of cellular T3 stainability. Results from radioimmunoassay of macrophage extracts also demonstrated that macrophages of low density had a higher level of total T3 than those of higher densities (greater than or equal to 1.060 g cm-3).

Acid phosphatase in lymphoid tissues of developing chick embryos

Activity of acid phosphatase (ACPase) in bursa and thymus has been determined in developing chick embryos of either normal or treated with bovine serum albumin (BSA). From the study of light microscopical histochemistry, ACPase activity could be detected in cytoplasm. These ACPase activities were detected in both the follicular medulla and cortex in bursa. In thymus, moderate ACPase activities were also obtained in both the cortex and medulla. ACPase activity in the tissue homogenate was increased in the bursa but the thymic ones showed constant level during the incubation days examined in normal embryos. ACPase distribution observed at the distinct developing stage indicates that ACPase is a useful parameter for growth and development of chicken lymphoid tissues.

Comparative interaction of free and liposome-encapsulated nor-muramyl dipeptide or muramyl tripeptide phosphatidylethanolamine (3H-labelled) with human blood monocytes

The purpose of this study was to analyse on biochemical and functional levels the interaction of free and liposome-encapsulated nor-muramyl dipeptide (nor-MDP) or muramyl tripeptide phosphatidylethanolamine (MTP-PE) with human peripheral blood monocytes. The activation of tumoricidal properties in monocytes by free MTP-PE required approximately 40-fold less material than free nor-MDP. Encapsulation of either MTP-PE or nor-MDP within multilamellar liposomes (MLV) increased the efficiency of the immunomodulators for activation of monocytes. The initial interaction of free 3H-nor-MDP or 3H-MTP-PE with monocytes was influenced by lipophilic derivatization, but neither derivatives exhibited characteristics of specific binding to the monocyte surface. The encapsulation of 3H-nor-MDP or 3H-MTP-PE within MLV increased uptake of both compounds by monocytes. The metabolic fate of MLV-entrapped 3H-nor-MDP was unaltered, but liposome encapsulation retarded the metabolism of 3H-MTP-PE. Collectively, the data suggest that the activation of monocytes by muramyl peptides results from an intracellular interaction which can be modulated by both lipophilic derivatization and/or liposome-encapsulation of this immunomodulator.

The differentiation antigens of macrophages in human fetal liver

Macrophage populations from human fetal liver were examined for the sequential appearance of different antigenic determinant during maturation. Frozen sections of liver, from 12 to 21 weeks gestation were analyzed using a series of four monoclonal antibodies with known specificity. The macrophage monoclonal antibodies used were OKM-1, which defines monocytes, macrophages, and granulocytes; Leu M-3 and MO-2, which identify monocytes and macrophages; and 6B8, a new macrophage monoclonal antibody which binds to tissue macrophages. The staining pattern described by each of these monoclonal reagents was compared with the distribution of morphologically distinguishable tissue macrophages in fetal liver, based on the expression of surface and/or cytoplasmic antigens. The data indicate that the antigens defined by OKM-1 and 6B8 are present on large numbers of cells as early as 12 weeks gestation. In contrast, the antigenic determinants identified by Leu M-3 and MO-2 are present only on cells in 15 to 21 weeks of gestation; thus these antigens are mature differentiation antigens. Furthermore, double-staining studies confirmed that with the increase in fetal age unique macrophage populations can be identified based on the matrix of antigenic determinants. Thus, macrophage heterogeneity in the fetal liver may be a function of maturation.

Binding of fibrinogen to human monocytes

The interaction of fibrinogen with monocytes was studied. After stimulation with ADP (10 microM) or thrombin (1 U/ml), platelet-free suspensions of human monocytes bind 125I-fibrinogen with two different affinities in a specific and Ca2+-dependent reaction with saturation at 5.80-7.35 X 10(-7) M of added protein. The binding of fibrinogen to specific receptors on monocytes induces the procoagulant activity of these cells. Thrombasthenic cells or normal monocytes preincubated with a monoclonal antibody to the platelet glycoprotein IIb/IIIa complex (10E5) do not bind fibrinogen and have no procoagulant activity. Metabolic studies with [35S]methionine revealed that cultured monocytes actually synthesize a surface antigen precipitated by 10E5 antibody as a major band with 92,000 relative molecular weight. Our data indicate that monocytes express receptors for fibrinogen only in part related to the platelet glycoprotein IIb/IIIa complex. Furthermore, the binding of fibrinogen to monocytes enhances the cooperation of these cells in hemostasis.

Extent of survival and vascularization of adult superior cervical sympathetic or nodose ganglia transplanted into the septal nuclei or choroid fissure of adult rats

Adult superior cervical sympathetic ganglia were auto-transplanted, and adult nodose ganglia were homografted into the septal nuclei or the choroid fissure of adult Wistar rats. At times from 4 h to 9 weeks after operation, the distribution of surviving transplanted neurons was compared with the development of the transplant vascularization, as visualized by transcardial Indian ink filling of the host vascular system. Within 24 h, the ganglionic neurons and Schwann cells of the interior of the transplants in both sites were necrotic. The surviving neurons and Schwann cells formed a shell, occupying those areas of the transplant periphery which were in direct contact with the host circulation. Occasional ink-filled vessels were evident at this time in transplants in the choroid fissure, but there were none in the septal nuclei, where vessels did not appear until the next day. Blood vessels reached the centre of the ganglia by 3-4 days in the choroid fissure and one week in the septal nuclei, the finest diameter capillaries forming last. At longer survivals there was a slow loss of neurons, notable between 1 and 2 months, and leading progressively (especially in the septal transplantation site) to the disappearance of all but a very small number of ganglionic neurons. The general findings were similar for both types of ganglion, and in both sites, but the initial cell loss was much greater for both types of ganglia in the septum (over 90%) as compared with about a 50% loss in the choroid fissure. The initial rapid cell loss was probably a result of ischaemia. The subsequent, slow progressive loss may be associated with failure to make or receive neuronal connections, or the absence of appropriate growth factors.

Serological determinants of fluorescent granular perithelial cells along small cerebral blood vessels in rodent

As reported previously, the perivascular cells laden with fluorescent granules (FGP cell) are situated in Virchow-Robin space and show marked uptake capacity for intraventricularly administered substances. The phagocytic FGP cells are derived developmentally form leptomeningeal cells and are recognizable in various kinds of animals, including humans. In the present paper, the FGP cells of rodents are studied by immunological techniques. It is clearly demonstrated that rat FGP cells express the antigenic determinant for Ia antibody at about 7 days after birth, and also that mouse FGP cells show a positive reaction against mouse Fc and splenic macrophage antibodies at about the same developmental stage. The specific determinants of FGP cells appear concurrently with the initiation of horseradish peroxidase uptake. On the other hand, Ia antigen is also shown in subarachnoid macrophages, but not in immature FGP cells, endothelium and pericyte. Based on these findings, it seems reasonable to consider that the FGP cells are indigenous cerebral macrophages and significant for the local immune response in a cerebral tissue. Further, in this paper, to prevent confusion of the FGP cell with the other perivascular cells, the authors propose designating the FGP cell as Mato cell.

DNA synthesis in the heterokaryons of non-dividing differentiated cells and culture cells with various proliferative potentials

Resident peritoneal mouse macrophages (non-dividing differentiated cells) were fused with mouse embryo fibroblasts (cells with a limited lifespan), NIH 3T3 and C3H 10T 1/2 cells ('immortal' cell lines) and SV 3T3 cells (a malignant cell line). DNA synthesis was investigated in the resultant heterokaryons. No inhibitory effect upon the transition of NIH 3T3 and mouse embryo fibroblasts nuclei to the S-phase was observed. C3H 10T 1/2, NIH 3T3 and SV 3T3 cells induced the reactivation of DNA synthesis in the macrophage nuclei in the heterokaryons. At the same time, no replication was detected in the macrophage nuclei after fusion with mouse embryo fibroblasts.

Studies of hypercholesterolemia in the nonhuman primate. II. Fatty streak conversion to fibrous plaque

This report presents the second portion of the morphologic studies on chronic, diet-induced hypercholesterolemia in nonhuman primates (Macaca nemestrina) examined sequentially between 5 and 13 months. A direct relationship was observed between the rate of cholesterol increase, the level and duration of hypercholesterolemia, and the changes in the artery wall that led to the formation of fatty streaks and their conversion to fibrous plaques. A loss of endothelial continuity was first observed in the iliac arteries between 3 and 4 months of atherogenic diet and appears to be a critical step in the conversion of many fatty streaks to fibrous plaques. With breaks in endothelial junctions and exposure of some of the macrophages in a fatty streak, many of the lipid-filled macrophages appeared to detach and enter the circulation. The number of circulating foam cells increased precipitously between 3 and 4 months, the time when increased sites of endothelial dysjunction and macrophage egress were observed. Exposure of subendothelial macrophages also permitted adherence of platelets to these macrophages and to exposed connective tissue. Fibrous plaques were found at similar anatomic sites where endothelial denudation had been observed at earlier time points but were more prevalent in the abdominal aorta and iliac arteries. These changes subsequently occurred at every level of the aortic tree and appeared to progress in a cephalad fashion with increasing rate, level, and duration of hypercholesterolemia. The results of these studies stress the importance of following cholesterol levels of each animal throughout the entire period of the study and of sampling the entire arterial tree at every level with time. This helped us to understand the complicated interrelationships between the various cells in atherogenesis, provided further support for the "Response to Injury Hypothesis of Atherosclerosis," and helped to explain how hypercholesterolemia may be involved in the different stages of atherogenesis in nonhuman primates and possibly in humans.

Cytostatic and cytolytic activities of macrophages regulation by prostaglandins

Murine peritoneal macrophages (M phi), activated in vivo or in vitro, remarkably inhibited the uptake of thymidine by a lens epithelial cell line, while resident M phi, or M phi induced by thioglycollate, exhibited much lower or no cytostatic capacity. The target cells were partially protected from the cytostatic activity by the anti-inflammatory agents indomethacin, aspirin, and dexamethasone, but not by lipoxygenase inhibitors. The protective activity of indomethacin and aspirin, but not of dexamethasone, was completely counteracted by prostaglandin E2 (PGE2). Yet, PGE2 alone has no effect on the uptake of [3H]thymidine by lens epithelial cells. PGE1 resembled PGE2 in its effect on this system, whereas PGA2, PGB2, or PGF2 alpha had no detectable activity. The counteracting effect of PGE2 was mimicked by dibutyryl cAMP or by cholera toxin, an agent which increases cAMP levels. These findings suggest that PGEs are not direct cytostatic agents, but rather, are essential mediators for the development of the cytostasis. Activated M phi did not lyse cells of the original lens epithelial cell line, but caused substantial cytolysis of cells of a subline derived from it. In contrast to its aforementioned effect on the cytostasis, PGE2 inhibited the cytolytic activity of M phi. Thus, this study provides a first demonstration in a single system of the opposite effects of PGEs on M phi activity on target cells, i.e., mediating the cytostasis and inhibiting the cytolysis.

Analysis of normal and abnormal amniotic fluid cells in vitro by cinemicrography

Time-lapse cinemicrography has been used to study cell behaviour and movement in long- and short-term amniotic fluid cultures from various types of fetus. These included several with a neural tube defect (9 anencephalics, 5 spina bifidas, 2 encephaloceles), 1 with an abdominal wall lesion (omphalocele) and 9 controls with no open lesion. In short-term (less than 3 days) amniotic fluid cultures from normal fetuses, non-adherent squamous cells dominate, but there is a small population of cells which, in the longer term (approximately 4 weeks), will form colonies of epithelioid and fibroblastic cells. In addition, there is a further group, called 'AF' by Hoehn et al. (1974), which have the ability to form syncitial strands and are often multinucleated; these cells seem to be trophoblastic in origin. In contrast to the controls, short-term anencephalic cultures contained many adherent cells; these were mainly latex-particle-phagocytosing macrophages and neural cells. In long-term cultures, the neural cells dominate and differentiate into a range of recognizable forms whose type and behaviour seem to depend on cell density, time in culture and extent of cell-cell contacts. In the spina bifida and encephalocele cultures, there were initially far fewer adherent cells than in the anencephalic ones, but, after approximately 2 weeks in vitro, a range of neural cell types could be recognized in addition to those seen in the controls. In the context of prenatal diagnosis, the presence of neural cells certainly indicates that the fetus has a NTD, but the difficulty of standardizing culture conditions implies that any differential diagnosis on the basis or morphology and movement will be difficult. If, as seems likely, the AF cells of Hoehn et al. (1974) are indeed trophoblastic, amniotic fluids from the second trimester may provide a useful source of these cells.

Intraepithelial lymphocytes and macrophages in the human epididymis

The epididymides from 7 young adults and 5 older patients with prostatic cancer were investigated by means of light and electron microscopy. The existence of lymphocytes and macrophages between epithelial cells of various segments of the ductuli efferentes and the ductus epididymidis is proven, and the distribution and morphology of these cells are described. A possible relationship between these two intraepithelial cell types, as well as their presumptive role with regard to an immunological barrier-function are discussed.

Murine peritoneal macrophages support murine cytomegalovirus replication

Because there have been different conclusions regarding the susceptibility of murine macrophages to murine cytomegalovirus (MCMV) infection and replication, we have undertaken a detailed comparison of MCMV infection of macrophages with that of a permissive cell line, mouse embryo cells. Although both cell lines undergo productive infections with MCMV, there are marked differences in certain aspects of the viral replication which may account for some of the different conclusions regarding the MCMV cycle in macrophages. Although both cell lines produce MCMV after infection, the time course of the infection differed markedly between the cell types. Similarly, the proportion of infected macrophages that are releasing infection virions is much smaller than the proportion of a comparably infected mouse embryo cell culture. Tissue culture passage of MCMV first enhanced (after one passage) and then reduced the infectivity of the virus for macrophages in vitro. The delayed time course and lesser production at early intervals after infection of macrophage cultures could not be attributed to demonstrable inhibitors or to replication in contaminating fibroblasts in the macrophage cultures.

Susceptibility of blood-derived monocytes and macrophages to caprine arthritis-encephalitis virus

Permissiveness of blood-derived caprine monocytes to infection by caprine arthritis-encephalitis virus increased during in vitro cultivation and differentiation into macrophages, as evidenced by immunofluorescence and release of extracellular infectious virus. The degree of cell susceptibility to virus infection varied among individual goats, independent of age or breed. Caprine arthritis-encephalitis virus infection of macrophages in vitro resulted in no alteration of five characteristic functional activities.

Granulomatous inflammation--a review

The granulomatous inflammatory response is a special type of chronic inflammation characterised by often focal collections of macrophages, epithelioid cells and multinucleated giant cells. In this review the characteristics of these cells of the mononuclear phagocyte series are considered, with particular reference to the properties of epithelioid cells and the formation of multinucleated giant cells. The initiation and development of granulomatous inflammation is discussed, stressing the importance of persistence of the inciting agent and the complex role of the immune system, not only in the perpetuation of the granulomatous response but also in the development of necrosis and fibrosis.

Specialization of the macrophage plasma membrane at sites of interaction with opsonized erythrocytes

We incubated mouse peritoneal macrophages for 3-8 min at 37 degrees C with antibody-coated sheep erythrocytes and examined regions of close interaction between the two cell types by electron microscopy. At sites of focal macrophage-erythrocyte contact we observed a distinctive specialization of the macrophage plasma membrane consisting of a prominent subplasmalemmal band of electron-dense material, approximately 25-35 nm in thickness. In many instances, this band showed a periodic substructure similar to that seen in clathrin coats. Moreover, many slender erythrocyte processes penetrated into invaginations of the macrophage surface which were bristle-coated at their blind extremity. As previously shown for clathrin-coated pits, the segments of the macrophage plasma membrane beneath which the defense material was found were selectively resistant to the membrane-perturbing effect of the antibiotic, filipin. This structural specialization of the macrophage plasma membrane at sites of ligand-receptor interaction during immune phagocytosis of antibody-coated erythrocytes may represent the morphological counterpart of the zipper mechanism of phagocytosis previously demonstrated by functional studies.

The regulation of 3-hydroxy-3-methylglutaryl-CoA reductase activity, cholesterol esterification and the expression of low-density lipoprotein receptors in cultured monocyte-derived macrophages

Human blood monocytes cultured in medium containing 20% whole serum showed the greatest activity of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase and [14C]acetate incorporation into non-saponifiable lipids around the 7th day after seeding, the period of greatest growth. Although there was enough low-density lipoprotein (LDL) in the medium to saturate the LDL receptors that were expressed by normal cells at that time, HMG-CoA reductase activity and acetate incorporation were as high in normal cells as in cells from familial-hypercholesterolaemic (FH) patients. Both the addition of extra LDL, which interacted with the cells by non-saturable processes, and receptor-mediated uptake of acetylated LDL significantly reduced reductase activity and increased incorporation of [14C]oleate into cholesteryl esters in normal cells and cells from FH patients ('FH cells'), and reduced the expression of LDL receptors in normal cells. Pre-incubation for 20h in lipoprotein-deficient medium apparently increased the number of LDL receptors expressed by normal cells but reduced the activity of HMG-CoA reductase in both normal and FH cells. During subsequent incubations the same rate of degradation of acetylated LDL and of non-saturable degradation of LDL by FH cells was associated with the same reduction in HMG-CoA reductase activity, although LDL produced a much smaller stimulation of oleate incorporation into cholesteryl esters. In normal cells pre-incubated without lipoproteins, receptor-mediated uptake of LDL could abolish reductase activity and the expression of LDL receptors. The results suggested that in these cells, receptor-mediated uptake of LDL might have a greater effect on reductase activity and LDL receptors than the equivalent uptake of acetylated LDL. It is proposed that endogenous synthesis is an important source of cholesterol for growth of normal cells, and that the site at which cholesterol is deposited in the cells may determine the nature and extent of the metabolic events that follow.

Lysosomal enzymes in ocular tissues and diseases

Lysosomal enzymes are distributed widely in various ocular tissues. Among these tissues, the uvea and retina show the higher enzyme activities of acid phosphates, beta-blucuronidase, alpha-fucosidase, alpha-mannosidase, arylsulfatase, cathepsin D, cathepsin B and others. The particular role of lysosomal enzymes in the pathogenic processes of ocular diseases such as storage disease, uveitis, retinal degeneration, retinal detachment, corneal dystrophy and glaucoma is strongly suggested. The enzymes also have additional importance in ocular physiopathology.

Initial events during phagocytosis by macrophages viewed from outside and inside the cell: membrane-particle interactions and clathrin

The initial events during phagocytosis of latex beads by mouse peritoneal macrophages were visualized by high-resolution electron microscopy of platinum replicas of freeze-dried cells and by conventional thin-section electron microscopy of macrophages postfixed with 1% tannic acid. On the external surface of phagocytosing macrophages, all stages of particle uptake were seen, from early attachment to complete engulfment. Wherever the plasma membrane approached the bead surface, there was a 20-nm-wide gap bridged by narrow strands of material 12.4 nm in diameter. These strands were also seen in thin sections and in replicas of critical-point-dried and freeze-fractured macrophages. When cells were broken open and the plasma membrane was viewed from the inside, many nascent phagosomes had relatively smooth cytoplasmic surfaces with few associated cytoskeletal filaments. However, up to one-half of the phagosomes that were still close to the cell surface after a short phagocytic pulse (2-5 min) had large flat or spherical areas of clathrin basketwork on their membranes, and both smooth and clathrin-coated vesicles were seen fusing with or budding off from them. Clathrin-coated pits and vesicles were also abundant elsewhere on the plasma membranes of phagocytosing and control macrophages, but large flat clathrin patches similar to those on nascent phagosomes were observed only on the attached basal plasma membrane surfaces. These resulted suggest that phagocytosis shares features not only with cell attachment and spreading but also with receptor-mediated pinocytosis.

Effects of antiviral agents on murine cytomegalovirus-induced macrophage dysfunction

Infection of murine peritoneal macrophages with murine cytomegalovirus (MCMV) led to disruption of phagocytosis. This alteration of cellular behavior appeared to be an early event in viral replication appearing 24 to 36 h before virus production and 84 to 108 h before cell death. The effects of a variety of antiviral agents on both MCMV replication and MCMV-induced depression of phagocytosis were evaluated in vitro. Although all compounds thought to act by preventing viral DNA replication inhibited MCMV replication in macrophages, none prevented expression of virus-induced alteration of phagocytosis. Cycloheximide at 1 microM blocked viral replication and viral antigen expression and prevented depression of phagocytic activity.

Degradation by cultured monocyte-derived macrophages from normal and familial hypercholesterolaemic subjects of modified and unmodified low-density lipoproteins

Human blood monocyte-derived macrophages that had been cultured for 7 days in the presence of 20% whole human serum exhibited saturable degradation of low-density lipoprotein (LDL). This degradation could be abolished by pre-incubating the cells with a high concentration of LDL in the medium and increased by pre-incubating the cells in medium containing lipoprotein-deficient serum. Cells obtained from the blood of homozygous familial-hypercholesterolaemic (FH) patients only exhibited a low rate of non-saturable degradation of LDL, even when pre-incubated without lipoproteins. Thus the saturable degradation of LDL by normal cells was mediated by the LDL receptors that are defective in FH patients and little LDL was taken up and degraded through any of the other endocytotic processes present in macrophages. Degradation by normal cells pre-incubated with lipoprotein-deficient serum had a higher apparent affinity for LDL than that of cells maintained in whole serum, which suggests that incubation with lipoprotein-deficient serum may not only induce the formation of LDL receptors but may also have a direct effect on the receptors themselves. Monocyte-derived macrophages from normal and FH subjects showed similar saturable degradation of acetylated LDL and also of LDL complexed with dextran sulphate. Maximal degradation of each was in the same range as the degradation of unmodified LDL by normal cells, and was not increased if the cells were pre-incubated with lipoprotein-deficient serum.

Macrophage depletion using Cytodex

Cytodex (microcarrier) beads were adapted for use as an adhering surface to deplete macrophages from a mouse spleen cell population. Non-adherent cells recovered from the incubation of one mouse spleen with 50 mg of Cytodex showed good viability and had markedly reduced proliferative response to the T cell mitogens phytohemagglutinin and concanavalin A. Response to lipopolysaccharide was, however, less clearly affected. Peritoneal exudate cells, and adherent cells recovered from the Cytodex by trypsinization, were able to restore the mitogenic response of non-adherent cells.

Dissociation of intracellular lysosomal rupture from the cell death caused by silica

The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 mug silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 mug silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 mug/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 mug silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or A23187. Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins.

Cells involved in the middle ear defense system

Despite the high incidence and prevalence of otitis media, its pathogenesis is not thoroughly understood. In the last decade, many efforts have been made to provide a better understanding, and abundant information has become available. At the same time the field of immunology has advanced at an extremely rapid pace. We have followed the gradual cellular events in the defense reaction of the middle ear, utilizing eustachian tube obstruction to induce otitis. Seventy-five cats were divided in groups and sacrificed at intervals between one day and six months, and their temporal bones were studied. During an initial phase of inflammation, polymorphonuclears appear at three days in connective tissue; at the same time active fibroblasts synthesize tropocollagen and ground substance while epithelial cells secrete mucus and lysozymes. These cells, together with those involved in the mucociliary transport system and a patent functional eustachian tube, constitute the nonspecific system of defense. The transition cells are the macrophages which appear at one week to interact with T and B cells to produce the specific immune response. Plasma cells appear at two weeks to peak at one month with synthesis of immunoglobulins A, G and M. A secretory immune system is observed. At three and six months, lymphocytes are the predominant cells and occasional accumulations of mononuclears are observed. The reaction involves the entire middle ear, including mucoperiosteum, middle ear muscles and round window membrane. We believe that a better understanding of the middle ear defense system will lead in time to a practical clinical assessment of the immunological status during the evolution of each particular process or disease involving the middle ear, and a more rational approach to the treatment and, hopefully, prevention of chronic ear disease.