5'-Nucleotidase activity of mouse peritoneal macrophages. II. Cellular distribution and effects of endocytosis

Studies on the arginase, 5'-nucleotidase and lysozyme activity by monocytes from visceral leishmaniasis patients

Intracellular pathogenic protozoan infection like visceral leishmaniasis is considered in terms of the overall inflammatory response and the complex cellular interactions leading to formation of the activated macrophage. Analysis of the development of activation is facilitated when operationally defined stage of activation are characterized using a library of objective markers. There is a role of arginase in the immune response supporting its involvement in macrophage effector mechanism in vitro and in vivo. 5'-Nucleotidase a plasma membrane component has been cited as a biochemical correlate of macrophage function in an altered morphological and biochemical state of activation and stimulation. Depression in 5'-nucleotidase activity has been generally referred to as a characteristic marker of activated macrophages. Lysozyme or lysosomal enzymes are released into the endocytic or autophagic vacuole macrophage where they serve the purpose of intracellular digestion of engulfed or segregated materials. In the present study, we have studied levels of arginase and 5'-nucleotidase (marker for macrophage activation) in monocytes of active VL patients and healthy controls. Lysozyme a secretary product of macrophages was also measured in supernatants collected from monocytes of active VL patients and healthy controls. Elevated levels of 5'-nucleotidase were observed in supernatants of monocytes from active VL patients as compared to healthy controls. Low levels of arginase and lysozyme production by monocytes isolated from VL patients were observed as compared to healthy controls. Our studies suggest that low levels of arginase and elevated 5'-nucleotidase activity could be one of the mechanisms in the pathology of VL infection. Low lysozyme activity in patients may account for persistence of Leishmania parasites in VL infections.

Biochemical properties of Candida parapsilosis ecto-5'-nucleotidase and the possible role of adenosine in macrophage interaction

Candida parapsilosis is considered to be an emerging fungal pathogen because it is associated with an increasing range of infections. In this work, we biochemically characterized ecto-5'-nucleotidase activity on the surface of living, intact C. parapsilosis cells. At a pH of 4.5, intact cells were able to hydrolyze 5'-AMP at a rate of 52.44 ± 7.01 nmol Pi h(-1) 10(-7) cells. 5'-AMP, 5'-IMP and 5'-UMP were hydrolyzed at similar rates, whereas 5'-GMP and 5'-CMP hydrolyzed at lower rates. Enzyme activity was increased by about 42% with addition of Mg(2+) or Ca(2+), and the optimum pH was in the acidic range. An inhibitor of phosphatase activities, sodium orthovanadate, showed no effect on AMP hydrolysis; however, as expected, ammonium molybdate, a classical nucleotidase inhibitor, inhibited the activity in a dose-dependent manner. The results indicated that the existence of an ecto-5'-nucleotidase could play a role in the control of extracellular nucleotide concentrations.

Phagocytosis and fluid-phase pinocytosis

The generation, flow, directionality and fusion of phagocytic and fluid-phase pinocytic vesicles in cultured macrophages and fibroblasts are reviewed. Specific plasma membrane (PM) receptors, receptor mobility, contractile cytoplasmic elements and lipid composition of the PM serve to regulate the flow of large phagosomes into the perinuclear zone. Fluid-phase vesicles are constitutively generated and carry large quantities of PM, fluid and solutes into the cytoplasm. Quantitative information is cited on the rates of vesicular generation, fusion with other members of the vacuolar system, fluid and solute uptake, and digestion and solute release. The nature and composition of fluid-phase vesicles, phagocytic vacuoles and PM are compared. Once interiorized, PM and its component polypeptides rapidly cycle back to the cell surface. The flow rates of both the centrifugal and the centripetal compartments as well as the fate of a minor degradation pool are illustrated and compared to the turnover of individual membrane polypeptides. Implications of membrane flow for cell shape, motility and new PM insertion are discussed.

Divalent cation-activated ecto-ATPase activity of rat glomerular mesangial cells

Evidence is presented of a Mg2+ and Ca(2+)-activated ATPase at the surface of cultured rat glomerular mesangial cells. Substrate specificity was very low when different nucleoside-5'-triphosphates were examined. The apparent Km values were 0.46 and 0.32 mM for Mg(2+)-ATPase and Ca(2+)-ATPase, respectively. Inhibition studies have revealed that this enzyme is different from the (Na+ + K+)-ATPase and from the divalent cation activated mitochondrial ATPases. Culture in the serum-free medium markedly decreased ecto-ATPase activity. Con A treatment reduced at 50 micrograms/ml by 15% the Ca(2+)-ATPase activity. Endocytosis of serum-treated zymosan (STZ) did not significantly affect ecto-ATPase activity. In contrast, endocytosis of STZ by macrophages was accompanied by a biphasic response, an increase in Mg(2+)-ATPase and Ca(2+)-ATPase activities after ingestion of smaller amounts of STZ and a marked decrease after loading doses of STZ.

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)

In vivo inflammatory stimulation induces a transient change in the binding of thrombin to rat peritoneal macrophages

The binding of 125I-labeled thrombin to rat peritoneal macrophages isolated 20 h after the ip injection of thioglycollate broth or lipopolysaccharide decreased to 20% of the value found in resident macrophages due to a decrease in the number of receptors. The binding returned to normal values within a week after the injection. The decline parallelled more or less the Vmax for the 5'-nucleotidase activity. This decrease in the binding of thrombin could not be explained by an immigration of monocytes into the peritoneal cavity, since the binding of 125I-labeled alpha 2-macroglobulin-trypsin complex increased 4.5-fold in the same cell population due to an increase in the number of receptors, and blood monocytes do not bind alpha 2-macroglobulin-trypsin complex. The increase in the binding of alpha 2-macroglobulin-protease complex parallelled an increase in the incorporation of glucosamine, although the latter did not increase to the same extent. Engulfment of plasma membrane after phagocytosis did not result in a decreased binding of thrombin, but preincubation at 37 degrees C with concanavalin A caused a minor reduction in the binding. There was a positive correlation between the binding of alpha 2-macroglobulin-trypsin complex and the fraction of polymorphonuclear leukocytes in the peritoneal exudate and a negative correlation between the binding of thrombin and the fraction of polymorphonuclear leukocytes in the exudate, when the inflammation was induced by a milder stimulus, sterile NaCl, indicating a common signal for the polymorphonuclear leukocyte chemotaxis and the macrophage differentiation.

Purine and pyrimidine compounds in murine peritoneal macrophages cultured in vitro

Extracts of murine peritoneal macrophages were analysed by ion-pair reversed-phase high-performance liquid chromatography during incubation at 37 degrees C in vitro. Four-step gradient elution was applied to an ODS column (250 x 4.6 mm I.D.) at a flow-rate of 1.3 ml/min, allowing the separation of hypoxanthine, inosine, guanosine, adenosine, IMP, CDP, AMP, GDP, UDP, ADP, CTP, GTP, UTP and ATP within 50 min. Samples of 0.4 . 10(6)-0.5 . 10(6) cells were washed twice with RPMI 1640 medium and extracted with perchloric acid. Nucleotide concentrations of murine peritoneal macrophages did not change during incubation for 4 days in vitro.

Toxicity to alveolar macrophages in rats following parenteral injection of nickel chloride

Alveolar macrophages collected by pulmonary lavage from male Fischer-344 rats at intervals (1-72 hr) after NiCl2 injection (62-500 mumol/kg, sc) were tested by several techniques. Within 1 to 4 hr, the macrophages showed morphological and biochemical signs of activation (hypertrophy, ruffled plasma membrane, increased cyclic AMP concentration, and markedly diminished 5'-nucleotidase activity, assayed by concanavalin A inhibition). Functional impairment (reduced phagocytic activity) was first seen at 24 hr; lipid peroxidation (increased malondialdehyde concentration) was not detected until 48 hr. Dose- and time-related effects of NiCl2 on 5'-nucleotidase activity, phagocytic activity, malondialdehyde concentration, and nickel content of alveolar macrophages were observed 24 to 72 hr postinjection. Diminished cell viability occurred only at 72 hr after the highest dosage of NiCl2. In alveolar macrophages from 63NiCl2-treated rats, 63Ni was located primarily in the cytoplasm, based upon liquid scintillation counting and autoradiography; fractionations of macrophage cytosol by gel filtration chromatography showed that 63Ni was bound to several high- and low-molecular-weight constituents. This study demonstrates that sc administration of NiCl2 to rats caused nickel uptake into and activation of alveolar macrophages, followed by reduced phagocytic capacity. The alveolar macrophage was a cellular target for nickel toxicity following parenteral exposure to NiCl2.

Ecto-enzyme activity of human erythrocyte adenosine deaminase

Adenosine deaminase is found primarily in the cytoplasm of many cell types. In the human erythrocyte, about 30 per cent of the total adenosine deaminase activity is membrane associated, and about two-thirds of this is inactivated by treatment of intact erythrocytes with the nonpenetrating reagent diazotized sulfanilic acid, without affecting lactate dehydrogenase, a soluble cytoplasmic enzyme. This indicates that within the cell membranes, the catalytic site of about two-thirds of the adenosine deaminase faces the external medium, i.e., ecto adenosine deaminase. Localization of adenosine deaminase activity at the cell membrane is demonstrated directly by electron microscopy by use of the substrate 6-Chloropurine ribonucleoside, which is dechlorinated by adenosine deaminase to produce Cl-, which is precipitated at its locus of formation by added Ag+, and the precipitated AgCl converted into the electron dense Ag0 upon exposure to light. From the Hydropathic Profile of the amino acid sequence of adenosine deaminase it is evident that there are two hydrophobic domains of sufficient length to span a biological membrane, and it is proposed that these domains could function to anchor the enzyme to the membrane. The importance of adenosine deaminase is indicated by the fatal immuno-deficiency which results from untreated genetic adenosine deaminase deficiency. It may be important to determine whether the amount of ecto adenosine deaminase activity is better suited to assess the clinical status of adenosine deaminase deficient patients that the currently used total cellular enzyme activity.

Relations between plasma membrane and lysosomal membrane. 1. Fate of covalently labelled plasma membrane protein

To quantify the kinetics of the plasma membrane flow into lysosomes, we covalently labelled at 4 degrees C the pericellular membrane of rat fibroblasts and followed label redistribution to the lysosomal membrane using purified lysosomal preparations. The polypeptides were, either labelled with 125I by the lactoperoxidase procedure, or conjugated to [3H]peroxidase using bisdiazobenzidine as a bifunctional reagent. Both labels were initially bound to plasma membrane, as indicated by their equilibrium density in sucrose or Percoll gradients and their displacement by digitonin, as well as by electron microscopy. Upon cell incubation at 37 degrees C, both covalent labels were lost from cells with diphasic kinetics: a minor component (35% of cell-associated labels) was rapidly released (half-life less than 1 h), and most label (65%) was released slowly (half-life was 20 h for incorporated 125I and 27 h for 3H). Immediately after labelling up to 30 h after incubation at 37 degrees C, the patterns of 125I-polypeptides quantified by autoradiography after SDS-PAGE were indistinguishable, indicating no preferential turnover for the major plasma membrane polypeptides. The redistribution of both labels to lysosomes was next quantified by cell fractionation. At equilibrium (between 6 and 25 h of cell incubation) 2-4% of cell-associated 125I label was recovered with the purified lysosomal membranes. By contrast, when 3H-labelled cells were incubated for 16 h, most of the label codistributed with lysosomes. However, only 6% of cell-associated 3H was bound to lysosomal membrane. These results indicate that in cultured rat fibroblasts, a minor fraction of plasma membrane polypeptides becomes associated with the lysosomal membrane and is constantly equilibrated by membrane traffic.

Detection of ecto-5'-nucleotidase on rat B and T lymphocyte subpopulations using a monoclonal antibody in rosetting reactions

A mouse monoclonal antibody to rat 5'-nucleotidase (5N 4-2 McAb) was used in the direct anti-determinant rosetting reaction (DARR) to demonstrate the ecto-5'-nucleotidase molecule in preparations of rat lymphocytes. Results indicated that 35.5 +/- 7.5% of peripheral blood lymphocytes (PBL), 37.3 +/- 4.8% of lymph node cells (LN) and 37.0 +/- 8.5% of spleen lymphocytes expressed the 5N 4-2 antigen. Depletion studies and mixed rosetting reactions (MRR) showed that the 5N 4-2 antigen was mainly expressed on rat T lymphocytes rather than on B lymphocytes: In fact 59.6 +/- 3.2% (in PBL), 76.5 +/- 0.6% (in LN) and 67.1 +/- 1.3% (in spleen) of T lymphocytes exhibited the 5N 4-2 antigen compared to only 26.5 +/- 2.6% (in PBL), 34.0 +/- 2.1% (in LN) and 46.1 +/- 12.0% (in spleen) of B lymphocytes. As expected a strong association was found between the expression of 5N 4-2 antigen and 5'-nucleotidase enzyme activity on lymphocytes. Both 5N 4-2 positive cells and enzyme activity were preferentially exhibited in the T lymphocyte subpopulation, and 92% of the enzyme activity was observed in a 5N 4-2 antigen positive subpopulation.

Isolation and characterization of a serine esterase from cytolytic T cell granules

Cytotoxic T lymphocytes and lymphocytes with NK-like activity contain a serine esterase activity which has been localized to their cytoplasmic granules by cytochemistry and subcellular fractionation studies. The serine esterase-specific inhibitor 3H-DFP labels two protein species in the granules. The two proteins, referred to as serine esterases 1 and 2 (SE 1 and SE 2), migrate with Mr of 34-36 kd and 28-30 kd, respectively, under reducing conditions. SE 1 shows trypsin-like activity and has been purified to apparent homogeneity. Under nonreducing conditions, SE 1 has an Mr of 60-66 kd, suggesting that it may consist of two disulfide-linked subunits of 34-36 kd each. SE 1 cleaves fibrin and casein, has a pl greater than 10, and optimal activity at pH 8. The substrate specificity of SE 2 is not known. The serine esterase activity is secreted by lymphocytes that have been stimulated with the calcium ionophore A23187. The serine esterases described here could play an active role in cell-mediated killing.

Impaired Kupffer cell function precedes development of secondary amyloidosis

It has been demonstrated previously that the acute phase reactant, serum amyloid A (SAA), is subject to degradation by surface membrane-associated proteinases of peripheral blood monocytes. However, monocytes obtained from the blood of patients with amyloidosis degraded SAA incompletely, leaving a cleavage product that, biochemically and immunologically, resembled the amyloid protein A (AA) deposited in their tissues. To investigate the role of fixed macrophages in amyloidogenesis and to establish more definitively that amyloid deposition is attributable to faulty processing of the precursor protein rather than aberrant synthesis, secondary amyloidosis was induced in C57BL/6J mice by serial injections of casein. Kupffer cells (KC) were isolated from livers of mice that had received 0, 8, 13, 18, and greater than 30 injections of the stimulant. The cells were cultured with SAA for 4, 8, and 18 h and then subjected to electron microscopy and enzyme analyses. The medium was analyzed by SDS-PAGE to determine the amount of residual SAA and/or the appearance of AA. KC of healthy animals degraded SAA completely whereas KC of stimulated mice showed increasing amounts of residual SAA and the appearance of the AA cleavage product. The AA peptide appeared in KC cultures early during the course of casein injections and before any amyloid could be demonstrated in the organs of the stimulated mice. The addition of KC isolated from healthy mice to cultures that had produced AA eliminated the abnormal peptide. The results, indicate that defective KC function precedes amyloidosis. The abnormal AA cleavage product formed by such cells is still susceptible to hydrolysis by normal cells. In addition, ultrastructural evidence is presented that suggests that KC may also play a role in fibrillogenesis of the AA protein.

Isolation of plasma membrane from human blood monocytes. Subcellular fractionation and marker distribution

The isolation of plasma membrane from human peripheral blood monocytes is described. Monocytes were isolated by centrifugal elutriation, to eliminate an adherence step, thus minimizing functional and surface antigenic alterations to the cells. Monocytes were surface-labelled with a radiolabelled monoclonal antibody, 125I-WVH-1, and then disrupted by nitrogen cavitation. Membranes were separated according to equilibrium buoyant density by isopycnic centrifugation on a sucrose gradient. The subcellular membranes were localized using marker enzymes for the plasma membrane, 5'-nucleotidase and leucine 2-naphthylamidase (leucine aminopeptidase), and for intracellular membranes: galactosyltransferase (Golgi), arylsulfatase C (endoplasmic reticulum), monoamine oxidase (mitochondria), catalase (peroxisomes), beta-hexosaminidase and beta-glucuronidase (lysosomal vesicles) and lactate dehydrogenase (cytosol). The monoclonal antibody 125I-WVH-1 was shown to label the plasma membrane, as judged by known markers, and represents a highly specific trace label, applicable to the use of plasma membrane as an immunogen for monoclonal antibody production. The NAD-splitting enzyme, NAD+ nucleosidase, was detected and its presence on the plasma membrane was demonstrated. The subcellular localization of non-specific esterase in human mononuclear phagocytes is controversial. No evidence was found for alpha-naphthyl acetate esterase activity on the plasma membrane or in lysosomal vesicles. However, a membrane-bound esterase in fractions with properties similar to the smooth endoplasmic reticulum was detected.

Biochemical and functional alterations in macrophages after thermal injury

Biochemical and functional measurements of rat pulmonary alveolar macrophages were measured 4 h after 1 10-s, 26 to 28% total body surface area, full-thickness scald burn induced under ether anesthesia. Both phagocytic activity and capacity were significantly decreased to a comparable extent, whereas microbicidal activity was increased almost twofold in macrophages from the burned animals. Concurrent with the decreased phagocytic function was a marked impairment in chemotaxis and random migration of these cells when zymosan-activated serum was used as the chemoattractant. When biochemical parameters were examined, it was demonstrated that, on a per-cell but not total-protein basis, alveolar macrophages from burned animals had elevated levels of RNA, total protein beta-glucuronidase, acid phosphatase, and 5'-nucleotidase. These results raise the possibility that the increased pneumonitis in burned individuals may be due to more complex macrophage dysfunctions than impaired microbicidal activity, as was once thought. Alternatively, the biochemical and functional changes observed may be a reflection of a new population of macrophages appearing in the lungs after thermal injury.

NAD+ glycohydrolase, an ecto-enzyme of calf spleen cells

By using a sensitive fluorimetric assay of NAD+ glycohydrolase (EC 3.2.2.6), we showed that calf spleen cells are able to hydrolyse 1,N6-etheno-NAD+ given in the medium. The observed rates of substrate hydrolysis and product accumulation in the medium are equivalent. Moreover, the splenocytes are able to cleave the nicotinamide-ribose bond of a water-soluble polymer of NAD+, and their NAD+ glycohydrolase activity is fully inhibited by a high-molecular-weight Blue Dextran. Selective permeation of the cellular membrane digitonin revealed an intracellular pool of NAD+ glycohydrolase, which accounts for 25% of the total activity. We conclude that NAD+ glycohydrolase associated with the splenocytes has the characteristics of an ecto-enzyme.

Analytical subcellular fractionation of cultivated mouse resident peritoneal macrophages

Resident peritoneal macrophages of the mouse, cultivated for 3 d, have been studied by quantitative subcellular fractionation using differential centrifugation and density equilibration in linear gradients of sucrose. Density equilibration experiments were carried out on untreated cytoplasmic extracts, on cytoplasmic extracts treated with digitonin or sodium pyrophosphate, and on cytoplasmic extracts derived from cells cultivated for 24 h in the presence of Triton WR-1339. The enzyme distributions obtained distinguished six typical behaviors characteristic of distinct subcellular entities. Acid alpha-galactosidase and other acid hydrolases displayed the highest average velocity of sedimentation and equilibrium density. Culturing in a medium that contained Triton WR-1339 markedly decreased their density, most likely as a result of Triton WR-1339 accumulation within lysosomes. Cytochrome c oxidase and the sedimentable activity of malate dehydrogenase showed a narrow density distribution centered around 1.17, very similar under all the experimental situations; their rate of sedimentation fell within the range expected for mitochondria. Catalase was particle-bound and exhibited structure-linked latency (80 percent); it was released in soluble and fully active form by digitonin, but this required a much higher concentration than in the case of lysosomal enzymes. Differences relative to all the other enzymes studied suggest the existence of a particular species of organelles, distinctly smaller than mitochondria, and possibly related to peroxisomes. Many enzymes were microsomal in the sense that the specific activities, but not the yields, were greater in microsomes than in other fractions obtained by differential centrifugation. These enzymes were distinguished in three groups by their properties in density equilibration experiments. NAD glycohydrolase, alkaline phosphodiesterase I, and 5'-nucleotidase had low equilibrium densities but became noticeably more dense after addition of digitonin. The other microsomal enzymes were not shifted by digitonin, in particular N-acetylglucosaminyltransferase and galactosyltransferase, which otherwise equilibrated at the same position in the gradient. We assign the digitonin-sensitive enzymes to plasma membranes and possibly to related endomembranes of the cells, and the two glycosyltransferases to elements derived from the Golgi apparatus. Finally, alpha-glucosidase, sulphatase C, NADH cytochrome c reductase, NADPH cytochrome c reductase, and mannosyltransferase, equilibrated at a relatively high density but were shifted to lower density values after addition of sodium pyrophosphate. These properties support their association with elements derived from the endoplasmic reticulum.

Effect of rifampin, levamisole, and cytoplasmic protein antigen from Mycobacterium microti on 5'-nucleotidase production by guinea pig macrophages

A decline in 5'-nucleotidase production was observed in short-term tissue culture of guinea pig alveolar, peritoneal, splenic, and liver macrophages during exposure to 10(2) microM rifampicin, 1 microM levamisole, or 10 micrograms of cytoplasmic protein antigen extracted from Mycobacterium microti. Liver macrophage 5'-nucleotidase production was more significantly inhibited by the three agents. Cytoplasmic protein antigen from M. microti was the most potent inhibitor of 5'-nucleotidase production.

Measurement of 5'-nucleotidase in mouse peritoneal macrophages in listeriosis

5'-Nucleotidase activity in peritoneal macrophages of mice was measured both before and after infection with Listeria monocytogenes in hosts which possessed high or low anti-listerial resistance either due to a genetically determined trait or as a result of splenectomy. Reduction in enzyme activity was directly related to the degree of infection that developed in the hosts and hence was inversely related to the level of anti-listerial resistance observed. Basal 5'-nucleotidase activity was significantly lower in noninfected hosts that possessed high anti-listerial resistance, possibly reflecting a higher level of native macrophage activation in these hosts.

Oxidation of glucose by mouse peritoneal macrophages: a comparison of suspensions and monolayers

Macrophages, when maintained in vitro, take up glucose from the medium and oxidize it to CO2. The rate of oxidation of glucose varies considerably, depending on the physical state of the cell preparation. Cells in suspension oxidize glucose at a level six-fold that of cells in monolayers. The differences cannot be attributed to change in the rats of transport of glucose. On the other hand, an increase in intracellular glycogen (about three-fold) and free glucose plus glucose-6-P (many-fold) was found in the cells prepared as monolayers. During subsequent incubation with glucose-14C, this could be the cause of an isotope dilution effect and could explain the lower production of 14CO2 by the adherent cells. Since oxidation of glucose-1-14C to 14CO2 is used by many investigators to indicate the functional state of macrophages, we suggest close attention be paid to the system used, i.e., monolayers vs. suspensions.

Increased fluid pinocytosis, induced by action of platelet-derived growth factor on quiescent arterial smooth muscle cells, does not require increased cholesterol biosynthesis

In the current report we provide evidence that the increased rate of cholesterol biosynthesis mediated by platelet-derived growth factor in the cell cycle of monkey (Macaca nemestrina) arterial smooth muscle cells can be separated from the increased rate of fluid pinocytosis using inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase.

Metabolism of purines in macrophages. Effect of functional state of the cells

Ecto-5'-nucleotidase is known to be diminished markedly in activated compared to control mouse macrophages. The level of three purine nucleoside metabolizing enzymes, adenosine deaminase (EC 3.5.4.4), purine nucleoside phosphorylase (EC 2.4.2.1), and adenine phosphoribosyltransferase (EC 2.4.2.7) were measured in the sonicates of different populations of mouse peritoneal macrophages. Levels of adenine phosphoribosyltransferase and purine nucleoside phosphorylase in macrophages that were elicited with sodium caseinate or activated in vivo by prior intravenous injection of Listeria monocytogenes were eight times higher than those in resident cells. Levels of adenosine deaminase also tended to increase and were two times higher in elicited cells than in resident cells. The Km of each enzyme was the same in each cell population. The findings suggest that the levels of the ecto-5'-nucleotidase and of the intracellular enzymes are coordinated.

Plasma membrane polypeptides of resident and activated mouse peritoneal macrophages

With the lactoperoxidase/glucose oxidase-catalyzed iodination method, we have identified at least 19 exteriorly disposed plasma membrane polypeptides on mouse peritoneal macrophages, with molecular weights ranging from 12,000 to 290,000. Resident and inflammatory macrophages could be distinguished by qualitative and quantitative differences in the display of selected polypeptides, although the overall banding patterns were similar. Some of the labeled polypeptides were identified by immunoprecipitation.

Studies on the association of NAD glycohydrolase with membranes in calf spleen

The subcellular distribution of NAD glycohydrolase was studied by fractionation of calf spleen homogenates using differential and discontinuous density gradient centrifugations. The highest amount of NAD glycohydrolase activity was associated with microsomes, which in this tissue were found to contain, in addition to endoplasmic reticulum, a large proportion of vesicles derived from plasma membranes. The distribution pattern of NAD glycohydrolase was found to parallel that of plasma membrane markers. When microsomal vesicles were treated with digitonin, NAD glycohydrolase activity and plasma membranes specifically increased in density. We conclude that in calf spleen the bulk of NAD glycohydrolase is associated with plasma membranes. Microsomal NAD glycohydrolase was associated with sealed vesicles; its activity could not be increased by disruption of the sidedness of the vesicles. This result and further observations based on the known restricted permeability of biological membranes to charged substances, and on the activity of the enzyme with non-penetrating substrates and inhibitors, indicate that the NAD glycohydrolase active site is located on the exterior side of the vesicles. It is proposed that calf spleen NAD glycohydrolase is an ecto-enzyme.

Macrophage polykarya

Multinucleated giant cells are commonly found in a wide variety of inflammatory reactions. They are formed at sites of tissue injury by fusion of freshly exuded monocytes, the rate of fusion being dependent on a range of extracellular and intracellular factors. Electron miscroscopy shows that the pooled components of the fused monocytes are not randomly dispersed in the syncytium, but are highly reorganized into a functioning unit. In addition, histochemical and biochemical profiles of cell populations containing these polykarya display a range of metabolic activities, including DNA synthesis, which, on occasions, is followed by successful mitotic division and the formation of polyploid daughter cells. Fusion results in the loss of some surface receptors which in turn interferes with the phagocytic performance of polykarya, which is generally less pronounced than their mononuclear precurses. In addition, polykarya are not as actively motile as macrophages although phenomena of contact inhibition are less obvious. On the other hand, the multinucleate giant cells display prominent exocytosis which may aid in the degradation of extracellular material. The properties of macrophage polykarya contrast with macrophage homokarya produced in vitro. The latter are actively phagocytic, do not synthesize DNA, and have a longer half-life than the syncytia produced in chronic inflammatory reactions. It may well be that the polykarya in such reactions are not true homokarya.

Macrophage protein turnover. Evidence for lysosomal participation in basal proteolysis

1. Turnover of intracellular proteins in cultured mouse macrophages was found to be slightly accelerated by the omission of serum from the culture medium. Media containing 10% (v/v) or more of serum established basal degradation rates in the cultures. 2. Basal degradation rates varied considerably between experiments, probably as a result of variable activation in vivo of the macrophages. 3. The selective carboxyl proteinase inhibitor pepstatin, which appeared to enter the lysosomes of the cells by pinocytosis, gave a progressive inhibition of basal proteolysis up to a maximum of about 40%. Cellular cathepsin D was largely inhibited after 48h of cultivation with pepstatin (100 micrograms/ml). 4. Leupeptin and 7-amino-1-chloro-3-tosylamidoheptan-2-one are less selective proteinase inhibitors. They also induced 25--35% inhibition of degradation, but their actions may not have been restricted to lysosomes. 5. Several solutes and particles that are endocytosed by macrophages and stored in lysosomes induce some inhibition of basal proteolysis, whether or not they themselves are substrates for proteolysis. 6. Colchicine was without effect on protein degradation, but cytochalasin B and the local anesthetics lidocaine and procaine, all of which have effects on microfilaments, were significantly inhibitory. This inhibition may result from a decrease in the rate of autophagy, and thus of lysosomal proteolysis, due to prevention of microfilament action.

Effect of phosphate esters, nucleotides and nucleosides on 5'-nucleotidase of cultured mouse macrophages

Mouse peritoneal macrophages elicited by intraperitoneal injection of sodium caseinate exhibit low levels of ecto-5'-nucleotidase (E. C. 3.1.3.5) activity in contrast to macrophages obtained by peritoneal lavage. When elicited cells were cultured under standard conditions in the presence of serum, a 2.5-fold increase in 5'-nucleotidase activity was observed over a period of 48 hours. Addition of adenosine monophosphate to the culture medium led to an augmented (5-fold) increase in the specific activity (per unit cell protein) as well as an absolute increase (per culture plate) of 5'-nucleotidase. Other adenosine-containing compounds also had stimulatory effects. The levels of this enzyme thus appear to be regulated by the extracellular levels of adenosine nucleotides. The product of the enzymatic reaction--adenosine--when added to the medium exhibited a toxic effect on these cells--as did adenosine monophosphate. However, the former substance did not augment the increase in enzyme activity during culture. The toxic effect could be suppressed when the cells were cultured in the presence of uridine 5'-monophosphate. The latter substance also depressed the stimulation of enzyme activity due to AMP.

The evidence for the existence of chymotrypsin-like esterase activity in the plasma membranes of rabbit neutrophils and the specific chemotactic peptide binding activity of the subcellular fractions

1. Light- and heavy-plasma membrane fractions have been isolated from rabbit neutrophils and a chymotrypsin-like esterase has been shown to be present in these fractions. 2. The molecular weight of the chymotrypsin-like esterase of rabbit neutrophil plasma membrane was estimated to be about 200 000. 3. About 93% of the chymotrypsin-like esterase of the plasma membranes is esterase 1 and the susceptibility to potential inhibitors was similar in light- and heavy-plasma membrane. 4. Chemotactic peptide, [3H]formyl-norleucyl-leucyl-phenylalanine [3H]formyl-Nle-Leu-Phe) binding by subcellular fractions shows that the highest specific binding was observed in the light-plasma membrane was about 2-fold higher than the heavy-plasma membrane, about 37-fold higher than the nuclear fraction, about 3-fold higher than lysosomal fraction and about 10-fold higher than the microsomal fraction.

Plasma membrane localization and metabolism of alkaline phosphodiesterase I in mouse peritoneal macrophages

Alkaline phosphodiesterase I activity is demonstrable in lysates of mouse resident peritoneal macrophages (1.43 mU/mg), endotoxin-stimulated macrophages (1.36 mU/mg), and thioglycollate-stimulated macrophages (3.91 mU/mg), as well as in the lysates of several mouse cell lines. The enzyme showed little variation in culture, although serum deprivation caused a 50% decrease in enzyme activity. In each of the three macrophage types about 80% of the enzyme is inactivated by the diazonium salt of sulfanilic acid, indicating that this enzyme is a component of the plasma membrane. In thioglycollate-stimulated cells about the same fraction of enzyme can be inactivated with papain corroborating this assignment. The enzyme is inactivated with a half-time of 14.1 h in resident cells, but this is decreased to 8.2 h in endotoxin cells, and to 5.7 h in thioglycollate cells. These results are consistent with the hypothesis that the endogenous pinocytic rate is a major determinant of plasma membrane turnover. In addition, the different synthetic rates measured in resident and inflammatory cells support the concept that macrophage activation is a differentiative process leading to a qualitatively new cell type.

Differences in surface membrane ecto-ATPase and ecto-AMPase in normal and malignant cells. I. Decrease in ecto-ATPase in myeloid leukemic cells and the independent regulation of ecto-ATPase and ecto-AMPase

The hydrolysis of ATP and AMP by enzymes located on the external side of the plasma membrane (ecto-ATPase and ecto-AMPase) was studied in mouse myeloid leukemic cells, normal early myeloid cells, and normal mature granulocytes and macrophages. Nine clones of myeloid leukemic cells were used belonging to three groups that differ in their ability to be induced to differentiate by the differentiation-inducing protein MGI. These three groups consisted of MGI+D+ that can be induced to undergo complete differentiation, MGI+D- that can be induced to partially differentiate and MGI-D- with no induction of differentiation. The ecto-ATPase activity of normal early myeloid cells was similar to that of normal mature granulocytes and macrophages and higher than that of any of the leukemic cells. Among the leukemic cells, the MGI-D- cells had the highest level of ecto-ATPase activity. The behaviour of ecto-AMPase differed from that of ecto-ATPase. Some MGI-D- clones had a higher ecto-AMPase activity than normal cells and MGI+D- and MGI+D+ cells showed no detectable activity. Neither the ecto-ATP-ase nor ecto-AMPase activities changed after induction of differentiation in normal early myeloid or MGI+D+ leukemic cells. The results indicate that the myeloid leukemic cells had a decreased ability to hydrolyse external ATP, that there can be an independent regulation of ecto-ATPase and ecto-AMPase and that neither of these enzyme activities changed during differentiation.

5'-Nucleotidase activity of mouse peritoneal macrophages. I. Synthesis and degradation in resident and inflammatory populations

Mouse resident peritoneal macrophages display sufficient 5'-nucleotidase activity to hydrolyze 58 nm AMP/min per cell protein. This activity increases approximately 163 nm AMP/min per mg after 72 h in culture. The enzyme is renewed in unstimulated cells with a half-time of 13.9 h. The activity is not reduced by treatment of intact cells with a variety of proteolytic enzymes, including trypsin, pronase, urokinase, and plasmin. Cells obtained from an inflammatory exudate have diminished or absent levels of enzyme activity. Endotoxin-elicited cells display enzyme activitiy of 20.9 nm AMP/min per mg, while thioglycollate-stimulated macrophages have no detectable activity. The reduced level of activity in endotoxin-stimulated cells is due to their elevated rate of enzyme degradation, with a half-time of 6.9 h. Their rate of enzyme synthesis is essentially normal. No evidence for latent enzyme activity could be obtained in thioglycollate-stimulated cells, nor do these cells produce any inhibition of normal cell enzyme activity. Serum deprivation reduces the enzyme activity of resident cells to about 45% of control activity. These conditions do not significantly affect the rate of enzyme synthesis, but again are explainable by an increase in the rate of enzyme degradation. Pinocytic rate is elevated in endotoxin-stimulated cells which show a more rapid rate of enzyme degradation than unstimulated cells do. However, in serum-free conditions, the rate of enzyme degradation is doubled with no change in the pinocytic rate of the cells.