THE PARTICULATE HYDROLASES OF MACROPHAGES. I. COMPARATIVE ENZYMOLOGY, ISOLATION, AND PROPERTIES

Establishment and characterization of a human histiocytic lymphoma cell line (U-937)

A human hematopoietic cell line (U-937) with exceptional characteristics was derived from a patient with generalized histiocytic lymphoma. The morphology of the cell line was identical to that of the tumor cells in the pleural effusion from which the line was derived. Since Epstein-Barr virus (EBV) carrying diploid lymphoblastoid cell lines unrelated to the tumor population often become established in vitro from non-Burkitt lymphoma explants, several parameters were studied to discriminate the U-937 from such lines: morphology in vitro, growth characteristics, cytochemistry, surface receptor pattern, Ig production, lysozyme production, beta2-microglobulin production, presence of EBV genome and karyotype. In all these respects U-937 differed from prototype lymphoblastoid cell lines. The histiocytic origin of the cell line was shown by its capacity for lysozyme production and the strong esterase activity (naphtol AS-D acetate esterase inhibited by NaF) of the cells. It is therefore concluded that the U-937 is a neoplastic, histiocytic cell line.

[Studies on the activities of peptidases from human leucocytes, and human and guinea pig alveolar macrophages (author's transl)]

Peptidases activities were compared in human leucocytes, guinea pig and human alveolar macrophages. Seversl endo- and exopeptides were characterized; some of them were active at acid pH and others at neutral and alkaline pH. Leucocytes and alveolar macrophages had proteolygic activity for hemoglobin, fibrinogen, collagen and elastin. Using synthetic substrates, several enzymes were characterized: arylamidase, aminopeptidase, carboxypeptidases A and B and cathepsins A and C. The enzymatic activities were much higher in alveolar macrophages than in leucocytes.

The effect of steroids on differentiation and function of cultured, mononuclear cells

When monocytes had differentiated to macrophages during 8 days of culture in vitro without being exposed to steroids, neither the engulfement nor the digestion step of phagocytosis was found to be influenced by cortisol or the other steroids tested. This indicates that cortisol has no direct effect on the phagocytic function of macrophages in doses below 10(-1) mg/ml. Continuous exposure to cortisol during the period of differentiation resulted in a dose dependent inhibition of the differentiation of monocytes to macrophages. Testosterone, deoxycorticosterone and tetrahydrocortisol in concentration of 10(-1) mg/ml, tested in the same way were found to be toxic to the cells. In lower concentrations, however, these steroids were found to have no effect on the cultured cells. The impaired differentiation of monocytes is suggested as an additional explanation of the reduced number of macrophages appearing at the site of inflammation during cortisol treatment.

Ontogeny of adherent cells. I. Distribution and ontogeny of A cells participating in the response to sheep erythrocytes in vitro

An adherent (A) cell function required for the in vitro antibody-forming response to sheep erythrocyte (SRBC) antigen has been demonstrated in a culture medium enriched with nucleic acid precursors and 2-mercaptoethanol. The essential function is fulfilled best by adult adherent cells of the spleen, to some extent by bone marrow and perhaps lymph node A cells, and poorly or not at all by peritoneal or lung A cells. Ontogenetic studies reveal the absence or inhibition of neonatal A cell synergistic function in the in vitro response to SRBC. The capacity of splenic adherent cells to collaborate with column-separated nonadherent cells appears only from the third or fourth day after birth, with ratio indices reaching levels significantly greater than nonsynergistic background by the fifth day and showing little further increase until the second week of age.

Fibrinogen/fibrin on the surface of macrophages: detection, distribution, binding requirements, and possible role in macrophage adherence phenomena

The peritoneal cavity of guinea pigs proved to be a rich source of mononuclear cells (34-52%) with fibrinogen or fibrin (Fib) on their surface. The Fib was readily detected on the surface of viable cells in suspension by fluorescence microscopy using antisera to guinea pig fibrinogen. The fluorescent staining occurred either in a speckled distribution, similar to that of cytophilic IgG, or in a distinctive net-like pattern that probably represented fibrin formation on the cell surface. The binding of Fib to the cell surface required calcium, but not magnesium, in the medium and could occur in vitro during incubation in heparinized plasma that contained fibrinogen concentrations comparable to that in normal peritoneal fluid (0.58 mg/ml). Cell surface Fib was more susceptible to plasmin and trypsin digestion than surface cytophilic IgG. By morphologic and physiologic criteria, cells exhibiting surface Fib were chiefly, if not exclusively, macrophages. Granulocytes, erythrocytes, and lymphocytes from lymph node and thymus had no sppreciable Fib. Cells with surface Fib were rarely observed among mononuclear cells prepared by Ficoll-Hypaque sedimentation of guinea pig and human blood (1.4 and 4.6%, respectively). Pulmonary alveolar macrophages, functionally distinct from peritoneal macrophages, lacked surface Fib (0.8%). Polymerization of Fib on the surface of macrophages might participate in certain cell interactions, such as the adherence of peritoneal macrophages during the antigen-induced macrophage disappearance reactions. The unexpected finding of Fib binding to the surfaces of peritoneal macrophages raises the possibility of a biologically significant interaction between these cells and the clotting system.

[Comparative studies of the acid hydrolases of human leucocytes and human and guinea pig alveolar macrophages. I. Study of the activities of glycosidases, arylsulfatase and acid phosphatase (author's transl)]

Acid hydrolase activities were compared in human leucocytes, guinea pig and human alveolar macrophages. Several enzymes were characterized: N-acetyl-beta-D-glucosaminidase, N-acetyl-alpha- and beta-D-galactosaminidase, alpha and beta-D-galactosidase, alpha-D-mannosidase, alpha-L-fucosidase, beta-D-glucuronidase, neuraminidase, acid phosphatase and arylsulfatase. The enzymatic activities were lower in leucocytes than in alveolar macrophages, higher in human macrophages than in guinea pig macrophages, except for beta-D-glucuronidase, acid phosphatase and arylsulfatase activities.

In vitro synthesis of lysozyme by human and mouse tissues and leucocytes

Previous studies have shown that lysozyme can be detected in many body fluids, in extracts of tissues, and also in granulocytes, monocytes and macrophages. However, the sites of synthesis of lysozyme have not been defined. In the present report, the synthesis of lysozyme by tissues, and by defined cell populations cultured in vitro has been studied by detecting the incorporation of 14-C-labelled amino acids into lysozyme. This method detects only lysozyme newly synthesized during the incubation of the specimen and therefore shows unequivocally which tissues and cell types are capable of lysozyme synthesis. The validity of the method has been shown by parallel studies using an independent method to detect lysozyme production in vitro. In studies in humans and mice, lysozyme synthesis has been demonstrated in the mucosa of the respiratory and gastrointestinal tracts, and in lymphoid organs. In studies of defined cell populations, monocytes and macrophages (mononuclear phagocytes) have been shown to synthesize lysozyme. Granulocytes from peripheral blood contain lysozyme but do not synthesize it, and lymphocytes neither contain nor synthesize lysozyme. The present findings provide further evidence that lysozyme has an important role in the defence of the host against micro-organisms, and the findings suggest that lysozyme may reach its target by several routes. At an intracellular level it is delivered from lysosomes into the phagocytic granules of granulocytes and macrophages. Local synthesis of the mucous membranes contributes lysozyme to secretions. Synthesis and secretion by mononuclear phagocytes which reach a tissue in response to an inflammatory stimulus contribute lysozyme to the exudate, and the release of lysozyme from breakdown of granulocytes has the same effect.

Complement receptor lymphocytes. Analysis of immunoglobin on their surface and further evidence of heterogeneity

Mouse complement receptor lymphocytes (CRL) were detected by a rosetting method. The existence of an immunoglobulin class or subclass on the central rosetting cell wasstudied by immunofluorescence using rabbit antisera specific for mouse IgM, IgG1, IgG2a, IgG2b and IgA. Combining immunofluorescence for each immunoglobulin and for T cells with cytoxic removal of T cells, CRL were demonstrated to include immunoglobulin-bearing cells of all the classes and subclasses tested (IgM being the main one), a 'null' cell subpopulation, and some T cells. A scheme describingthe various nature of CRL is discussed and correlated with possible functions.

Pathways of clearance in mouse lungs exposed to iron oxide aerosols

The history of particle clearance was studied in lungs of mice serially sacrificed at intervals up to 14 months following single exposures to an aerosol of submicronic, particulate, iron oxide used as a similitude for atmospheric dust. Clearance was followed by light microscopy in unstained and Prussian blue stained frozen and plastic embedded sections, as well as by electron microscopy, where iron oxide can be recognized by its form. Related problems were investigated through histochemical demonstration of acid phosphatase activity in pulmonary lysosomes and Prussian blue staining of various tissues after administration of iron compounds by gastrointestinal and vascular routes. The iron particles settle extensively but not uniformly on pulmonary alveolar surfaces. Clearance is centripetal and involves two mechanisms, an extracellular mechanism fed by fluid currents sweeping across the surfcace, and cellular mechanism principally involving alveolar macrophages. In the early post exposure period both actively remove deposited particles predominantly through the pulmonary airways. By 24 hours uncleared residues have become ingested and clearance thereafter results mainly from cellular action. Macrophages enter bronchial passages where they sometimes continue to pursue normal activities. A chronic phase of clearance begins when deposited particles become sequestered in macrophages of pulmonary connective tissues. These cells are reached by several routes, not least by crossing the bronchial epithelium. Particle clearance from these macrophages is very slow, and residue-containg cells eventually congregate in lymphoid tissues surrounding major bronchi. These findings are discussed as they help to develop an overall picture of clearance from the lungs and as they bear on related topics, such as functional roles of alveolar and pulmonary connective tissue macrophages and the pathogenesis of chronic bronchial disease.

Studies with human leukocyte lysosomes. Evidence for antilysosome antibodies in lupus erythematosus and for the presence of lysosomal antigen in inflammatory diseases

Human lysosomes were isolated from normal peripheral blood leukoyctes and characterized by electron microscopy, enzyme analysis, and assays for DNA and RNA. Stored sera from 37 unselected patients with systemic lupus erythematosus (SLE), including active and inactive, treated and untreated cases, were tested in complement fixation (CF) reactions with these lysosome preparations. 23 SLE sera exhibited positive CR reactions, as did sera from two patients with "lupoid" hepatitis. The seven SLE sera with strongest CF reactivity also demonstrated gel precipitin reactions with lysosomes. Neither CF nor precipitin reactions with lysosomes were observed with normal sera or with sera of patients with drug-induced lupus syndrome, rheumatoid arthritis (RA), polymyositis, or autoimmune hemolytic anemia. By several criteria the antilysosome CF and precipitin reactions of SLE sera cound not be attributed to antibody to DNA, RNA, or other intracellular organelles. The lysosomal component reactive with SLE sera in CF assays was sedimentable at high speed and is presumably membrane associated. The CF activity of two representative SLE sera was associated with IgG globulins by Sephadex filtration. A search for lysosomal antigen in SLE and related disorders was also made. By employing rabbit antiserum to human lysosomes in immunodiffusion, a soluble lysosomal component, apparently distinct from the sedimentable (membrane-associated) antigen described above, was identified in serum, synovial fluid, or pleural fluid from patients with SLE, RA, ankylosing spondylitis, and leukemoid reaction. An antigenically identical soluble component reactive with the rabbit antiserum could be released in vitro from intact lysosomes by repeated freeze-thaw cycles..

Rosette formation by mouse lymphocytes. II. T-cell specificities in a CRL subpopulation

Mouse spleen and lymph node lymphocytes with receptors for complement (CRL) were prepared by a standard rosetting method and the identity of the central lymphocyte studied by indirect immunofluorescence with heterologous antisera specific for immunoglobulin and for T cells. About 30% of CRL were shown to be T cells and the remainder immunoglobulin-bearing (B) cells.

In thymus-less `nude' mice a population of immunoglobulin-negative, non-T cell CRL was found.

The role of cathepsin D in the pathogenesis of tuberculosis. A histochemical study employing unlabeled antibodies and the peroxidase-antiperoxidase complex

Cathepsin D was visualized in free pulmonary alveolar macrophages (AM), in oil-induced peritoneal macrophages (MN) and in rabbit pulmonary and dermal BCG lesions with unlabeled antibodies and the peroxidase-antiperoxidase (PAP) complex. Large amounts of cathepsin D were present in AM and lower amounts in MN. In the lung this enzyme was richest in the alveolar macrophages that accumulated around the BCG lesions. In the dermal lesions, cathepsin D was in highest concentration in macrophages at the border of the necrotic (liquefying) centers. It was also found in high concentration in keratinizing cells of the dermal epithelium and hair follicles. It did not, however, increase appreciably in many of the activated macrophages that stained intensely for the lysosomal enzyme beta-galactosidase. In fact, many epithelioid cells with high beta-galactosidase activity contained no visible cathepsin D. This proteinase does not, therefore, seem to be primarily involved in the lymphocyte-mediated macrophage activation associated with acquired cellular resistance to tubercle bacilli. It is probably more involved with cell autolysis, with the digestion of ingested necrotic debris and, in all likelihood, with the process of liquefaction, the most adverse event in the pathogenesis of tuberculosis in man.

Erythrocyte catabolism by macrophages in vitro. The effect of hydrocortisone on erythrophagocytosis and on the induction of heme oxygenase

Phagocytosis of erythrocytes was studied in vitro in an incubation system consisting of rat peritoneal macrophages and antibody-coated (59)Fe-labeled erythrocytes. The system was characterized in terms of the rate and magnitude of erythrophagocytosis, determined by the interiorization of the (59)Fe label. On incubation of 150 x 10(6) macrophages with 75 x 10(6) antibodycoated erythrocytes, erythrophagocytosis began within a few minutes and was essentially completed after 2 h when 50% of the offered red cells had been ingested by the macrophages. Heme oxygenase (HO) activity, which is very low in native macrophages, increased 4- to 10- fold in response to the ingested erythrocytes; this enzyme stimulation occurred with a delay of 3 h in relation to erythrophagocytosis. Actinomycin D or puromycin prevented the increase of HO activity without affecting erythrophagocytosis, which suggests that the enzyme stimulation was due to substrate-mediated enzyme induction. Hydrocortisone (HC) (0.1 mg/ml medium) dissociated erythrophagocytosis from HO induction, leaving the former unimpaired but completely suppressing the latter. The suppressive effect of HC on the enzyme induction was completely prevented by 5 mg glucose and 0.02 U insulin/ml of the medium. In macrophages engaged in erythrophagocytosis. HC also lowered glucose removal from the medium and reduced formation of (14)CO(2) from [1-(14)C]glucose. These results suggest that induction of HO in macrophages by the hemoglobin of ingested erythrocytes requires intact transport or metabolism of glucose. Glucose utilization appears to be impaired by HC, but is restored by additional glucose and insulin. The findings suggest that plasma steroid concentrations in the pharmacological range could reduce bilirubin formation in phagocytic cells in vivo without affecting the sequestration and degradation of erythrocytes. This provides a possible explanation for the observation that in patients with hepatogenous jaundice, steroids often lower the serum bilirubin level.

The heterogeneous distribution of acid hydrolases within a homogeneous population of cultured mammalian cells

1. Chinese-hamster ovary fibroblasts were cultured to provide a homogeneous cell population. Homogenates obtained from these cells were fractionated by centrifugation techniques and the resulting fractions were analysed for protein and for enzymes representative of certain subcellular particles. 2. Unlike those in rat liver homogenates, the mitochondrial and lysosomal populations proved impossible to separate by differential centrifugation owing to the similarity of their sedimentation properties. Their resolution was possible by using isopycnic centrifugation in a continuous sucrose density gradient. 3. The mitochondrial population equilibrated at a density of 1.17g.cm(-3) as in rat liver homogenates. However, the lysosomal population equilibrated at a lower rather than a higher density position than the mitochondria and the probable reasons for this are discussed. 4. The lysosomal population subdivided into two groups characterized by differences in acid hydrolase content and equilibrium densities. The fraction with a density of 1.15g.cm(-3) contained the majority of arylsulphatases A and B, of cathepsin and of beta-acetylglucosaminidase activities, whereas that with a density of 1.09g.cm(-3) contained the majority of the acid phosphatase and acid ribonuclease activities. The probable division of the lysosomal population of a single cell into a number of distinguishable subgroups is suggested.

Comparative densities of hydrolase-containing granules from normal and BCG-induced alveolar macrophages

Compared to cells from normal rabbit lungs, BCG-induced alveolar macrophages have a marked increase in hydrolase levels and the number of large electron-dense subcellular structures. This study was performed to investigate the possibility that these electron-dense structures were responsible for the increased hydrolase levels of these cells. Using sucrose gradient centrifugation, nuclei-free homogenates of normal and BCG-induced macrophages were analyzed with respect to the subcellular particles they contain. Gradient fractions were assayed for enzymes commonly associated with lysosomes as well as the mitochondrial cytochrome oxidase. Fractions of peak hydrolase activity from the BCG-induced preparations were consistently more dense than those from the normal cell preparations. Ultrastructural studies of the particulate material found in fractions of peak hydrolase activity from BCG-induced preparations revealed the presence of electron-dense, often dumbbell-shaped, granules. The data suggest that these peculiar granules are responsible for the elevated hydrolase levels of BCG-induced alveolar macrophages.

Effect of methylprednisolone on some BCG-mediated changes in rabbit alveolar macrophage

The effect of methylprednisolone sodium succinate treatment on Bacillus Calmette-Guérin (BCG) immunization was examined in alveolar macrophages of New Zealand White rabbits. Intravenous BCG injection caused a marked increase in cell number and in the hexosemonophosphate shunt activity. There was also a selective augmentation in the activity of acid phosphatase and beta-glucuronidase and an increase in lysosomal density. Activity of the lysosomal phospholipases was decreased. Steroid treatment suppressed the BCG-induced increase in cell number, hexosemonophosphate shunt activity, acid phosphatase, and beta-glucuronidase, and prevented the increase in lysosomal density. On the other hand, steroid treatment increased the activity of the phospholipases to levels higher than either control values or those obtained with cells from BCG-treated rabbits.

Lysosomes in rat thoracic duct lymphocytes

10 acid hydrolases known to be lysosomal in other tissues were detected in rat thoracic duct lymphocytes (TDL). Except for cathepsin D, all these enzymes occurred in lower levels in TDL than in rat spleen. Fractionation by means of differential centrifugation revealed two types of distribution patterns. Most of the total cathepsin D activity appeared in a high-speed supernatant (S), whereas the other acid hydrolases associated mainly with a high-speed pellet (P). Further studies by isopycnic centrifugation in a sucrose density gradient showed that all the enzymes, including a small portion of cathepsin D, sedimented around a modal density of 1.18. In contrast, most cathepsin D activity was recovered in a soluble, unsedimentable form. These results suggest the presence of two populations of lysosomes. Because the possibility could be excluded that other cell types contaminated the lymphocyte preparations, it is concluded that both lysosomal populations arise from TDL.