Effects of concanavalin A on mouse peritoneal macrophages. I. Stimulation of endocytic activity and inhibition of phago-lysosome formation

The Use of Adenovirus Dodecahedron in the Delivery of an Enzymatic Activity in the Cell

Penton-dodecahedron (Pt-Dd) derived from adenovirus type 3 is a symmetric complex of pentameric penton base plus fiber which can be produced in the baculovirus system at a high concentration. The size of Pt-Dd is smaller than the virus, but this virus-like particle (VLP) has the major proteins recognized by specific receptors on the surface of almost all types of cell. In this study, by direct observation with fluorescence microscopy on a fixed and living cell, the intracellular trafficking and localization of Pt-Dd labeled with fluorescence dyes in the cytoplasm of HeLa Tub-GFP showed a rapid internalization characteristic. Subsequently, the linkage of horseradish peroxidase (HRP) with Pt-Dd as the vector demonstrated an efficient system to deliver this enzyme into the cell without interfering its enzymatic activity as shown by biochemical and cellular experiments. These results were supported by additional studies using Bs-Dd or free form of the HRP used as the control. Overall, this study strengthens the potential role of Pt-Dd as an alternative vector for delivering therapeutic agents.

The venom of South American rattlesnakes inhibits macrophage functions and is endowed with anti-inflammatory properties

The injection of Crotalus durissus terrificus venom into the foot pad of mice did not induce a significant inflammatory response as evaluated by oedema formation, increased vascular permeability and cell migration. The subcutaneous injection of the venom, or its addition to cell cultures, had an inhibitory effect on the spreading and phagocytosis of resident macrophages, without affecting the viability of the cells. This effect was not observed when the venom was added to cultures of thioglycollate elicited macrophages, but it was able to inhibit these macrophage functions when the cells were obtained from animals injected simultaneously with the venom and thioglycollate. These observations suggest that the venom interferes with the mechanisms of macrophage activation. Leukocyte migration induced by intraperitoneal injection of thioglycollate was also inhibited by previous venom injection. This down-regulatory activity of the venom on macrophage functions could account for the mild inflammatory response observed in the site of the snake bite in Crotalus durissus terrificus envenomation in man.

Liposomal-glutathione provides maintenance of intracellular glutathione and neuroprotection in mesencephalic neuronal cells

A liposomal preparation of glutathione (GSH) was investigated for its ability to replenish intracellular GSH and provide neuroprotection in an in vitro model of Parkinson's disease using paraquat plus maneb (PQMB) in rat mesencephalic cultures. In mixed neuronal/glial cultures depleted of intracellular GSH, repletion to control levels occurred over 4 h with liposomal-GSH or non-liposomal-GSH however, liposomal-GSH was 100-fold more potent; EC(50s) 4.75 μM and 533 μM for liposomal and non-liposomal-GSH, respectively. Liposomal-GSH utilization was also observed in neuronal cultures, but with a higher EC(50) (76.5 μM), suggesting that glia facilitate utilization. Blocking γ-glutamylcysteine synthetase with buthionine sulfoxamine prevented replenishment with liposomal-GSH demonstrating the requirement for catabolism and resynthesis. Repletion was significantly attenuated with endosomal inhibition implicating the endosomal system in utilization. Liposomal-GSH provided dose-dependent protection against PQMB with an EC(50) similar to that found for repletion. PQMB depleted intracellular GSH by 50%. Liposomal-GSH spared endogenous GSH during PQMB exposure, but did not require GSH biosynthesis for protection. No toxicity was observed with the liposomal preparation at 200-fold the EC(50) for repletion. These findings indicate that glutathione supplied in a liposomal formulation holds promise as a potential therapeutic for neuronal maintenance.

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.

Lectin-based food poisoning: a new mechanism of protein toxicity

Background

Ingestion of the lectins present in certain improperly cooked vegetables can result in acute GI tract distress, but the mechanism of toxicity is unknown. In vivo, gut epithelial cells are constantly exposed to mechanical and other stresses and consequently individual cells frequently experience plasma membrane disruptions. Repair of these cell surface disruptions allows the wounded cell to survive: failure results in necrotic cell death. Plasma membrane repair is mediated, in part, by an exocytotic event that adds a patch of internal membrane to the defect site. Lectins are known to inhibit exocytosis. We therefore tested the novel hypothesis that lectin toxicity is due to an inhibitory effect on plasma membrane repair.

Methods and Findings

Repair of plasma membrane disruptions and exocytosis of mucus was assessed after treatment of cultured cell models and excised segments of the GI tract with lectins. Plasma membrane disruptions were produced by focal irradiation of individual cells, using a microscope-based laser, or by mechanical abrasion of multiple cells, using a syringe needle. Repair was then assessed by monitoring the cytosolic penetration of dyes incapable of crossing the intact plasma membrane. We found that cell surface-bound lectins potently inhibited plasma membrane repair, and the exocytosis of mucus that normally accompanies the repair response.

Conclusions

Lectins potently inhibit plasma membrane repair, and hence are toxic to wounded cells. This represents a novel form of protein-based toxicity, one that, we propose, is the basis of plant lectin food poisoning.

Importance of acyl-coenzyme A:cholesterol acyltransferase 1/2 dual inhibition for anti-atherosclerotic potency of pactimibe

Pactimibe sulfate, [7-(2,2-dimethylpropanamido)-4,6-dimethyl-1-octylindolin-5-yl]acetic acid hemisulfate, a novel Acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitor, was investigated in vitro and in vivo to characterize its potential. Pactimibe exhibited dual inhibition for ACAT1 and ACAT2 (concentrations inhibiting 50% [IC50s] at micromolar levels) more potently than avasimibe. Kinetic analysis revealed pactimibe is a noncompetitive inhibitor of oleoyl-CoA (Ki value: 5.6 microM). Furthermore, pactimibe markedly inhibited cholesteryl ester formation (IC50: 6.7 microM) in human monocyte-derived macrophages, and inhibited copper-induced oxidation of low density lipoprotein more potently than probucol. Pactimibe exerted potent lipid-lowering and anti-atherosclerotic effects in atherogenic diet-fed hamsters. At doses of 3 and 10 mg/kg for 90 days, pactimibe decreased serum total cholesterol by 70% and 72%, and aortic fatty streak area by 79% and 95%, respectively. Despite similar cholesterol lowering, fatty streak area reduction was greater by 10 mg/kg. These results suggest that ACAT1/2 dual inhibitor pactimibe has anti-atherosclerotic potential beyond its plasma cholesterol-lowering activity.

Lectins inhibit the Aujeszky's disease virus-induced interferon-alpha production of porcine peripheral blood mononuclear cells

The interaction between virus and peripheral blood mononuclear cells (PBMC) required to elicit the production of interferon-alpha (IFN-alpha) by the so-called natural interferon-producing cell is unknown. However, results from inhibition experiments suggest that viral glycoproteins are essential in this IFN induction process. We demonstrate here that cellular glycoproteins also appear to be involved in the initiation of IFN-alpha production. Lectins, that is, sugar binding glycoproteins, inhibited the Aujeszky's disease virus-induced IFN-alpha production of porcine PBMC by up to 99%. The level of inhibition varied with lectin used (concanavalin A, Galanthus nivalis lectin, Helix pomatia lectin, and lentil lectin). Preincubation experiments with porcine cells and concanavalin A (ConA) revealed that the lectin exerted its major effect directly on the PBMC. Although the IFN-alpha production in some cases was reduced by more than 90%, the PBMC were still able to proliferate in response to mitogenic lectins. The ConA-mediated inhibition of the IFN-alpha production was reduced if the lectin was added later than 6-8 h after the start of induction and was not mediated by soluble factors. Both orthovanadate and staurosporine inhibited the IFN-alpha production and did not relieve the ConA-mediated inhibition. Thus, ConA seems to interfere with the early events during IFN-alpha induction, but the mechanisms behind this interference could not be clarified.

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)

Adsorptive endocytosis and membrane recycling by cultured primary bovine brain microvessel endothelial cell monolayers

The dynamics of membrane recycling were examined in primary cultures of brain microvessel endothelial cells (BMECs). Because the BMEC surface was dominated by galactosylated glycoconjugates, ricin agglutinin (RCAI) was used as a tracer to follow the endocytosis and recycling of RCAI binding sites. These binding sites accounted for 75% of the iodinatable or most externally disposed plasma membrane proteins. Because greater than 90% of the RCAI that had bound to BMECs was removed by a brief, nontoxic treatment with galactose, the amounts and kinetics for internalization and efflux of [125I]RCAI were measured. Both endocytosis and efflux were energy dependent. By using pseudo-first-order kinetics, the t1/2 values for RCAI binding, internalization and efflux were 5, 18 and 13-14 min, respectively. By comparing efflux with and without galactose present, we found that 60% of the RCAI binding sites that had been internalized were returned to the cell surface and reinternalized. Quantifying the distribution of gold-RCAI following internalization showed kinetics consistent with that obtained using radiolabeled RCAI. Both horseradish peroxidase (HRP) and gold-conjugated RCAI that had bound BMEC at 4 degrees C became localized within more caveolae within 2.5 min of warming to 37 degrees C to permit endocytosis. With time, RCAI appeared within endosomes and tubules and vesicles of which some were located in the trans-Golgi network (TGN). The distribution of HRP-RCAI contrasted with that of free HRP, which was not routed to the TGN. The absence of RCAI conjugates in association with the basolateral membrane domain suggested the presence of functional tight junctions and maintenance of polarity throughout the duration of these experiments. These results showed that membrane recycling was more extensive and much slower than fluid-phase endocytosis in cultured BMECs. Moreover, we found that endocytosis of membrane by BMECs in culture was similar to that reported for brain endothelium in vivo in that a fraction of the cell surface membrane was routed to the TGN.

Rapid endocytosis and recycling of wheat germ agglutinin binding sites on CHO cells: evidence for two compartments in a nondegradative pathway

The internalization and recycling of CHO cell plasma membrane components have been quantified by using iodinated wheat germ agglutinin (WGA) as an adsorptive tracer. Most of these binding sites are thought to be composed of a subpopulation of plasma membrane proteins called high-molecular-weight acidic glycoproteins (HMWAG). Greater than 90% of the WGA bound on the cell surface can be removed by brief treatment with N-acetylglucosamine (GlcNAc). At 37 degrees C, endocytosis of WGA that had been allowed to bind to the surface at 4 degrees C is curvilinear with an initial rapid phase occurring with a t1/2 of 6-8 min. Within 20 min, accumulation has slowed gradually to steady-state with 65% of the cell-associated WGA located intracellularly or resistant to removal by GlcNAc. These portions are unaffected by increasing the extracellular concentration of WGA from 0.003 microM to 2.8 microM. By using pulse-chase experiments, the observed decrease in rate of endocytosis is shown to be due to return of the WGA-HMWAG complexes to the cell surface. More than 60% of the WGA that had been internalized is recycled within 30 min, with a mean t1/2 of 17 min. Recycling involved at least two intracellular populations where a significant fraction (less than 30%) of the WGA-HMWAG complexes are lost gradually from the rapidly recycling pool. Most of the WGA-HMWAG complexes that had internalized are not delivered to the lysosome. These results demonstrate the magnitude of rapid and continuous recycling of WGA binding sites between the cell surface and endosomes in fibroblasts.

Endocytosis of wheat germ agglutinin binding sites from the cell surface into a tubular endosomal network

By using fluorescence and electron microscopy, the endocytic pathway encountered by cell surface components after they had bound wheat germ agglutinin (WGA) was visualized. The majority of these components are thought to consist of sialylated glycoproteins (HMWAG) that represent a subpopulation of the total cell surface proteins but most of the externally disposed plasma membrane proteins of the cell. Examination of semi-thin sections by medium- and high-voltage electron microscopy revealed the three-dimensional organization of vesicular and tubular endosomes. Binding of either fluorescein isothiocyanate-, horseradish peroxidase-, or ferritin-conjugated WGA to cells at 4 degrees C showed that the HMWAG were distributed uniformly over the cell surface. Warming of surface-labeled cells to 37 degrees C resulted in the endocytosis of WGA into peripheral endosomes via invagination of regions of both coated and uncoated membrane. The peripheral endosome appeared as isolated complexes comprising a vesicular element (300-400 nm diam.) surrounded by and continuous with tubular cisternae (45-60 nm diam.), which did not interconnect the endosomes. After 30 min or more label also became localized in a network of anastomosing tubules (45-60 nm diam.) that were located in the centrosomal region of the cell. Endocytosed WGA-HMWAG complexes did not become associated with cisternae of the Golgi apparatus, although tubular and vesicular endosomes were noted in the vicinity of the trans-Golgi region. The accumulation of WGA-HMWAG in the endosomes within the centrosomal region was inhibited when cells were incubated at 18 degrees C. None of these compartments contained acid phosphatase activity, a result that is consistent with other data that the HMWAG do not pass through lysosomes initially. The kinetics of labeling were consistent with the interpretation that recycling of most of the WGA binding surface glycoproteins occurred rapidly from early peripheral endosomes followed by the late trans-Golgi compartment. In conclusion, a portion of cell surface glycoproteins are routed to a complex arrangement of tubular and vesicular compartments following endocytosis that includes a putative post-endosomal, tubular reticulum that appears to be separate from the trans-most Golgi saccule.

Emperipolesis in a case of malignant lymphoma: electron microscopic and immunohistochemical investigation

In the tissue sections of axillary lymph nodes surgically removed from a case of malignant lymphoma (non-Hodgkin's, diffuse, large cell type), many large cells were observed to contain lymphoma cells in their cytoplasm. From the findings of light microscopy in serial sections and electron microscopy, this phenomenon was confirmed to be "emperipolesis." By immunohistochemistry, the large cells that contained lymphoma cells possessed most of the monocyte/macrophage markers, whereas the lymphoma cells revealed some B-cell markers, suggesting that they were of germinal center cell origin. In a survey of the literature, we found no report describing emperipolesis in the tissue sections of malignant lymphoma. Although the precise mechanisms and biological significance of emperipolesis in the present case are not fully understood, the existence of some interactions between macrophages and lymphoma cells is suggested.

Phorbol ester stimulates macrophage invasion of fibrin matrices

Macrophages migrate through a fibrin-rich extracellular matrix in chronic inflammation, wound healing, and other pathophysiological processes. To investigate the factors that might influence the ability of mononuclear phagocytes to invade fibrin matrices, we cultured macrophage-like P388D1 cells as well as resident and thioglycollate-elicited mouse peritoneal macrophages on three-dimensional fibrin gels, and we examined the effect of agents known to stimulate a variety of macrophage functions, including the production of fibrinolytic enzymes. Cells grown on fibrin gels under control conditions, as well as cells treated with either bacterial lipopolysaccharide or concanavalin A, remained confined to the gel surface. In contrast, the tumor promoter 4 beta-phorbol 12-myristate 13-acetate (PMA) induced both P388D1 cells and peritoneal macrophages to invade the underlying fibrin matrix. The invasive behavior of PMA-treated P388D1 cells was not affected by protease inhibitors of various specificities. These results demonstrate that certain exogenous signals can profoundly modify the ability of macrophages to migrate through fibrin matrices.

Receptor-mediated O2- release by alveolar macrophages and peripheral blood monocytes from smokers and nonsmokers. Priming and triggering effects of monomeric IgG, concanavalin A, N-formyl-methionyl-leucyl-phenylalanine, phorbol myristate acetate, and cytochalasin D

Receptor-mediated superoxide (O2-) release by alveolar macrophages and peripheral blood monocytes from smokers and nonsmokers was studied in vitro. When the cells were incubated with monomeric IgG or monomeric Fc(IgG) fragment, no cell O2- release was observed. However, when cytochalasin D (Cyto D) was subsequently added to the cell suspension, we observed a markedly enhanced O2- release. Neither Cyto D alone nor the double stimulation of following Cyto D with monomeric IgG induced O2- release. Concanavalin A (Con A) also had a priming effect on O2 release in combination with Cyto D, as did monomeric IgG or monomeric Fc(IgG) fragment. On the other hand, heat-aggregated IgG, N-formyl-methionyl-leucyl-phenylalanine (FMLP), or phorbol myristate acetate (PMA) induced O2- release without the addition of Cyto D. Thus, we observed 2 different mechanisms in the receptor-mediated O2- release by alveolar macrophages and peripheral blood monocytes. Alveolar macrophages from smokers, which had a higher affinity and a larger number of monomeric IgG binding sites per cell than those from nonsmokers, were more reactive to the double stimulation of following monomeric IgG with Cyto D than to that of Con A and Cyto D, FMLP, or PMA, but for peripheral blood monocytes it was the reverse. We conclude that the binding of monomeric IgG to the Fc(IgG) receptor of alveolar macrophages or peripheral blood monocytes results in a priming effect on the cells for O2- release, and that the regulation of receptor-mediated O2- release by alveolar macrophages differs at least in part from that of peripheral blood monocytes.

Effects of cholesterol and lipoproteins on endocytosis by a monocyte-like cell line

The human monocyte/macrophage-like cell line U937 is a cholesterol auxotroph. Incubation of these cells in the growth medium in which delipidated fetal calf serum has been substituted for fetal calf serum depletes cellular cholesterol and inhibits growth. The cholesterol requirement of these cells for growth can be satisfied by human low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL), but not by high-density lipoprotein (HDL). U937 cells can bind and degrade LDL via a high-affinity site and this recognition is altered by acetylation of LDL. This indicates that these cells express relatively high LDL receptor activity and low levels of the acetyl-LDL receptor. The cells were used to study the role of cholesterol in lectin-mediated and fluid-phase endocytosis. Growth of the cells in the medium containing delipidated fetal calf serum results in impairment of both concanavalin A-mediated endocytosis of horseradish peroxidase and concanavalin A-independent endocytosis of Lucifer Yellow. Supplementation of the medium with cholesterol prevents cellular cholesterol depletion, supports growth and stimulates Lucifer Yellow endocytosis but fails to restore horseradish peroxidase endocytosis. However, if the cells are incubated in the presence of no less than 40 micrograms LDL protein/ml to maintain normal cell cholesterol levels, concanavalin A-mediated endocytosis of horseradish peroxidase is activated. The effect of LDL is specific since neither VLDL nor HDL3 at the same protein concentration activates horseradish peroxidase uptake by the cells. Furthermore, the activation of endocytosis by LDL is not inhibited by the inclusion of heparin or acetylation of the LDL indicating that binding of LDL to the LDL receptor is not required for these effects. The mediation of activation of horseradish peroxidase endocytosis by the lectin is presumed to involve binding of LDL to concanavalin A associated with the cell surface which in turn stimulates horseradish peroxidase binding and uptake by adsorptive endocytosis. The rate of fluid endocytosis and endosome formation seems to depend on cellular cholesterol content presumably because cholesterol is involved in maintaining the appropriate plasma membrane structure and fluidity.

Induction of microvillous fusion and pinching-off by concanavalin A

Concanavalin A (Con A) caused dramatic changes in the structure and function of rat colonic epithelium. The morphological effect was a pronounced, permanent alteration of the microvilli, including fusion and blebbing. The functional change involved an increased permeability to passively transported hydrophilic marker compounds. The functional change was transient in nature. Since coadministration of glucose or mannose inhibited the effect of Con A, the mechanistic effect of Con A probably involves binding to saccharide components of the membrane surface.

Lysosomal involvement in cellular intoxication with Clostridium difficile toxin B

The process of internalisation of Clostridium difficile toxin B into human lung fibroblasts was further studied, with the aim of elucidating the fate of endocytosed toxin. Development of the toxin-induced cytopathogenic effect was reversibly inhibited at 18 degrees C and in the presence of 200 mM KCl or 1-20 mM benzyl alcohol, i.e. at conditions when the fusion between endosomes and lysosomes is prevented. Fibroblasts treated with toxin at 37 degrees C but transferred to 18 degrees C within 10 min were also completely protected, whereas transfer to 18 degrees C later during the latency resulted in only partial protection. KCl was also protective upon addition after the toxin binding step. Inhibitors of lysosomal proteases, such as chymostatin, leupeptin and antipain, prevented the appearance of the cytopathogenic effect, when present during toxin exposure or added after the toxin binding step. Chinese hamster ovary cell mutants, defective in acidification of their endosomes, were resistant to toxin B, whereas wildtype cells were sensitive. The resistance was not overcome by applying a low extracellular pH. The results suggest that exposure to a low pH compartment is necessary but not sufficient for entry of active toxin B to the cytosol. In addition to a low pH, a fusion of toxin-containing endosomes with lysosomes and a further processing of the toxin by lysosomal proteases is required for cellular intoxication.

Movements and other distinguishing features of small vesicles identified by darkfield microscopy in living macrophages

Perinuclear vesicles (estimated diameter less than 0.15 micron), too small to be seen in living mouse macrophages by direct phase-contrast microscopy, could be detected by darkfield microscopy thanks to their rapid non-saltatory movements at 37 degrees C, contrasting with the slower saltations of accompanying phase-visible larger vesicles (0.25-0.5 micron, presumed secondary lysosomes). The movements of these 'small visicles' also differed from those of the 'larger visicles' in their responses to changes in temperature, and to chemical agents known to inhibit both the saltations of secondary lysosomes and the latter's fusion with phagosomes. Thus the 'larger vesicles' stopped moving at 25 degrees C, the small ones did not; both stopped at 18 degrees C. The 'small vesicles' continued to move actively after cell uptake of the polyanion poly-D-glutamic acid, while the saltations of the 'larger vesicles' were markedly slowed; both sets of vesicles stopped after uptake of ammonium chloride. Degranulation of the small vesicles paralleled that of the larger, while simultaneously observed preformed pinosomes (labelled with fluorescent wheat germ agglutinin (WGA) appeared to be unaffected. On the basis also of refractivity, location and speed the 'small vesicles' are considered not to be pinosomes, but probably to be lysosomes. The question of whether they are a subgroup of small immature secondary lysosomes or primary lysosomes (0.05-0.08 micron) is discussed. The broad spectrum of movement inhibited by ammonia in macrophages raises the possibility that this weak base inhibits movements of all lysosomes. Further characterization of these 'small vesicles' requires their relation to be defined to the small particles in other cell types (especially in axoplasm) which have been detected by video-enhanced microscopy.

Recombinant and natural gamma-interferon activation of macrophages in vitro: different dose requirements for induction of killing activity against phagocytizable and nonphagocytizable fungi

Recombinant murine gamma-interferon (IFN) and supernatants from concanavalin A (ConA)-stimulated spleen cells were tested for their ability to activate resident peritoneal macrophages (M phi) for fungicidal activity. M phi monolayers pulsed overnight with IFN exhibited significantly enhanced fungicidal activity against Candida albicans (44 +/- 12 versus 0.0%) and Blastomyces dermatitidis (34 +/- 1 versus 3 +/- 3%). The effect of IFN was dose dependent; however, less IFN (10 U/ml) was required to activate M phi to kill phagocytizable C. albicans than to kill nonphagocytizable B. dermatitidis (1,000 U/ml). ConA-stimulated spleen cell supernatants were also able to activate M phi for fungicidal activity against both fungi. The capacity of ConA-stimulated spleen cell supernatants to activate M phi for fungicidal activity was neutralized in the presence of antibody to murine IFN. ConA-treated monolayers acquired the ability to kill C. albicans, but not B. dermatitidis, which was shown to be associated with residual (10%) lymphocytes in the monolayers. Lipopolysaccharide (0.001 to 10 micrograms/ml) failed to consistently activate M phi for fungicidal activity. These data show that IFN can exert an immunoregulatory role on M phi defense against these fungal pathogens.

The in vitro activity of lectin I from mistletoe (ML I) and its isolated A and B chains on functions of macrophages and polymorphonuclear cells

We investigated the effects of ML I and its isolated chains, A and B, in regard to selected functions of phagocytes (human granulocytes, paraffin-oil stimulated M phi from guinea pigs). On these cells, ML I has no cytotoxic effect between 10(-14) and 10(-8) (trypan blue exclusion and ethidium bromide exclusion). Over the same concentration range, ML I and B chain diminish the negative surface charge of M phi and agglutinate M phi at concentrations greater than or equal to 2 X 10(-8) M (ML I) and greater than or equal to 3 X 10(-7) M (B chain), respectively. The diminishing of the negative surface charge shows two peaks, indicating the existence of two types of receptors on the M phi surface with different affinities for sugar-binding sites. Moreover, the B chain shows a third peak at higher concentrations (3 X 10(-8) M) that could be inhibited by D-galactose (greater than or equal to 10(-4) M). In comparison, the A chain reduces the surface charge at concentrations over 3 X 10(-7) M, but D-galactose has no effect on this. By means of the agarose droplet test, the spontaneous migration of M phi is inhibited in the sequence ML I much greater than B chain greater than A chain. The phagocytic activity of human leukocytes tested with a radiometric phagocytosis technique reveals an increasing effect only for the B chain; ML I and the A chain have no effect. Perhaps the mechanism of the described activities of ML I and its B chain are comparable with the action of lymphokines activating M phi.

Effect of concanavalin A on intracellular killing of Staphylococcus aureus by human phagocytes

This study concerns the influence of concanavalin A (Con A) on phagocytosis and intracellular killing of Staphylococcus aureus by human monocytes and granulocytes. Con A binds to S. aureus, monocytes, and granulocytes, and is not opsonic. Con A stimulates the killing of intracellular serum opsonized S. aureus by monocytes, but not by granulocytes. This stimulation of intracellular killing was inhibited by alpha-methyl-mannoside, indicating that the process occurs via Con A specific membrane binding sites. Unlike (tetravalent) Con A, divalent succinyl-Con A does not stimulate intracellular killing, indicating that the lectin valency is important for this stimulation. Con A bound to Sephadex particles, that can not be ingested by monocytes, does not stimulate intracellular killing of S. aureus either, although it, like free Con A, stimulates H2O2 production. Pre-incubation of monocytes with Con A inhibited Fc gamma and C3b-mediated ingestion of S. aureus as well as stimulation of the killing by serum. Divalent Con A had no effect on these functions. This inhibition by Con A is in all probability due to a steric impedance of Con A with respect to the interaction of IgG and C3b with their membrane receptors. Fluorescence techniques showed that Con A was localized on the membrane and in the cytoplasm of the monocytes, whereas granulocytes had only membrane bound lectin. Taken together, these findings suggest that cell penetration by the lectin is obligatory for the stimulation of intracellular killing.

Binding of concanavalin A and wheat germ agglutinin by murine peritoneal macrophages: Ultrastructural and cytophotometric studies

Concanavalin A and wheat germ agglutinin were employed in conjunction with the horseradish peroxidase-diaminobenzidine method for the detection of sugar residues on the surface coat of exudate and resident murine peritoneal macrophages. Electron microscopical and cytophotometric techniques were used for the visualization and quantification of the final reaction product on the surface of cells. After incubation with concanavalin A and wheat germ agglutinin, both exudate and resident macrophages showed readily detectable final reaction product indicating the presence of numerous, easily accessible, alpha-methyl-D-mannosyl and N-acetyl-D-glucosaminyl residues on their surface. The binding of concanavalin A was higher with resident than with exudate macrophages. With wheat germ agglutinin, a different pattern of lectin binding was observed: more electron-dense product was deposited on exudate than on resident macrophage surfaces. The binding of concanavalin A and wheat germ agglutinin to macrophages was inhibited by the competing sugars alpha-methyl-D-mannoside and N-acetyl-D-glucosamine, respectively.

Exclusion of erythrocyte-specific membrane proteins from clathrin-coated pits during differentiation of human erythroleukemic cells

When human erythroleukemic cells are induced to differentiate, they produce globin and redistribute glycophorin and spectrin to one pole of the cell. This process was accompanied by an alteration in the clathrin-coated pits at the cell surface. In nondifferentiating cells, receptors for Concanavalin A have been shown, using electron microscopy, to be concentrated into coated pits and rapidly internalized. Glycophorin was also internalized via coated pits, but was not greatly concentrated into these portions of the surface membrane. Ligands attached to glycophorin were, therefore, cleared from the cell surface more slowly than Concanavalin A. In nondifferentiating cells, immunoelectron microscopy showed that spectrin is largely excluded from coated pits. After erythroid differentiation proceeded for several days, glycophorin was totally excluded from the coated pits along with spectrin. This did not reflect a general cessation of endocytosis, however, because Concanavalin A receptors continued to be internalized. It is possible that the specific exclusion of glycophorin from coated pits is part of the remodeling process that occurs when the precursor cell membrane differentiates into that of the mature erythrocyte.

Isolation and characterization of internalized glioma cell membranes

A method for isolating plasma membranes based on the ability of cultured C6-glioma cells to phagocytize inert material such as polystyrene (latex) beads is described. The beads (phi 1.1 micron) were incubated for 16 h or 5 h. After several washings and homogenization of the cells, the beads with the surrounding membranes were isolated by use of a sucrose density gradient. The membranes were analyzed morphologically and biochemically. Morphological studies by means of light- and electron microscopy confirmed the intracellular localization of the beads. Enzymatic studies revealed that the specific activity of acid phosphatase decreased with shorter incubation periods (from 268.00 +/- 38.56 U X mg protein-1 X min-1 after 16 h to 125.12 +/- 9.10 after 5 h), whereas that of Na, K-ATPase showed the opposite trend (3.63 +/- 0.41 and 4.73 +/- 0.78 mumoles phosphate X mg protein-1 X h-1, respectively), indicating a lesser contamination with lysosomes. The main advantages of this procedure for membrane studies lie in purity and definite orientation ("inside-out") of the membranes.

A time-lapse video image intensification analysis of cytoplasmic organelle movements during endosome translocation

Vital fluorescence staining has been used in conjunction with time-lapse video image intensification microscopy to analyze the distribution and movement of endosomes, lysosomes, and mitochondria in cultured rat ovarian granulosa cells. Exposure of 5-d granulosa cell cultures to pyrene-concanavalin A (P-Con A) or 3,3'-dioctadecylindocarbocyanine-labeled low-density lipoprotein (dil-LDL) at 4 degrees C results in the formation of randomly distributed endosomes 10 min after warming to 37 degrees C that exhibit saltatory motion for 20 min. If granulosa cells are labeled at 4 degrees C with both P-Con A and dil-LDL and warmed to 37 degrees C, both ligands are found within the same endosomes which migrate centripetally to the cell center where label accumulates within phase-dense structures by 60 min. The initial endosome saltations occur over short distances (mean distance = 4.6 micron) with a mean velocity of 0.03 micron/s. Endosome saltations then cease and are followed by a gradual centriptal migration of endosomes to the cell center where they accumulate and fuse with phase-dense structures. The second phase of movement involves a continuous, unidirectional migration of endosomes over distances ranging from 5 to 40 micron at a mean velocity of 0.05 micron/s. Lysosomes were simultaneously visualized as acridine orange-staining, phase-dense structures in control cells and cells exposed to fluorescent ligands. In untreated cells, lysosomes are dispersed throughout the cytoplasm and undergo bidirectional saltations covering a mean distance of 8.7 micron with a mean velocity of 0.3 micron/s. Lysosomes redistribute centripetally to the perinuclear region of the cell by saltatory movement within 20 min of exposure to ligand. Mitochondria were visualized with the fluorescent dye rhodamine 123 in granulosa cells labeled with P-Con A and were found to redistribute to the cell center coincident with endosomes. The microtubule-disrupting agent nocodazole was found to inhibit lysosome saltations and all phases of endosome movement. Taxol, a microtubule-stabilizing agent, partially impaired lysosome movement and led to a redistribution of lysosomes into linear aggregates surrounding the nucleus. Taxol was also found to inhibit endosome movement. The data indicate that (a) endosome movement proceeds initially by saltation and later by a nonsaltatory centripetal migration in association with mitochondria, that (b) lysosomes and endosomes undergo a temporally distinct but spatially similar change in cytoplasmic distribution, and that (c) microtubules are required for the directed translocation of endosomes and lysosomes towards the cell center.

Promoting effect of concanavalin A on transport of sodium cefoxitin and phenol red from rat rectal compartment

Concanavalin A enhanced the rat rectal absorption of phenol red and cefoxitin at pH 7.4 and the uptake of cefoxitin into brush border membrane vesicles prepared from rat rectal membrane. The enhancing action of concanavalin A demonstrated a sodium ion dependency and was inhibited by the presence of 4,4'-diisothiocyano-2,2'-disulfonate stilbene and phlorizin. This inhibition suggests the involvement of the membrane protein fraction.

The effects of sucrose loading on lysosomal hydrolases

The addition of 88 mM sucrose to the culture medium of human skin fibroblasts from normal subjects caused remarkable increase in the intracellular lysosomal hydrolase activities. The mechanism of this induction by sucrose loading was carefully studied with several fibroblast strains of different inherited lysosomal storage disorders. In single lysosomal hydrolase defect such as GM1-gangliosidosis, mannosidosis and Sandhoff disease, no induction of the deficient hydrolase was found with 88 mM sucrose loading. In contrast, sucrose loading caused normalization of intracellular lysosomal hydrolase activities in I-cell disease fibroblasts and cytoplasmic inclusion materials disappeared. Subsequent investigations reveal that I-cell disease cells are classified into three subgroups by the degree of hydrolase induction by sucrose loading; a high responding, an intermediate responding and a no-response group. The heterogeneity may be based upon different induction by sucrose loading of the enzyme, probably the residual phosphotransferase which is involved in the processing steps of lysosomal enzyme molecules. With the addition of mannose-6-phosphate and 10 mM NH4Cl to cultured skin fibroblasts, it was shown that sucrose loading caused increased synthesis of lysosomal enzyme proteins. The result of the test with 2,4-dinitrophenol suggests that sucrose is indeed pinocytosed by cultured human skin fibroblasts and localized in lysosomes and that this event is the essential factor to trigger the induction of lysosomal hydrolases. Simultaneous loading of both invertase and sucrose in cultured cells caused no induction of alpha-mannosidase activity. This result indicates that invertase is also pinocytosed, reaches the lysosomes and hydrolyzes sucrose in the lysosomes. Lysosomal overloading with sucrose resulted in induction of lysosomal hydrolases and invertase blocked the induction of alpha-mannosidase activity. However, some induction still exists in beta-galactosidase and alpha-fucosidase activity. Thus it is very likely that the induction of lysosomal hydrolases demands a complicated process. In this article, we investigated the effects of sucrose on the lysosomal hydrolases in cultured human skin fibroblasts of several inherited lysosomal storage disorders and normal subjects and discuss the possible mechanism of the induction of lysosomal hydrolase activities by sucrose loading.

pH in the endosome. Measurements during pinocytosis and receptor-mediated endocytosis

By fluorescence spectroscopy, the average pH within endocytic compartments was determined during endocytosis of fluorescein conjugates by macrophages and hepatocytes. In mouse macrophages and hepatocytes fluorescein conjugates taken up either in the fluid phase or by binding to cell surface receptors were rapidly transferred to an acidic compartment (pH 5-5.5). The half-time for this process was generally less than 4 min. The pH within yeast-containing phagosomes was also rapidly reduced to similar levels, following a unique and transient increase. In each case, the acid endosomal compartments involved probably do not contain lysosomal enzymes. When fluorescein conjugates of asialoglycoproteins were internalised by hepatocytes at 20 degrees C, no proteolysis occurred within the acidic endosome until the temperature was raised. Fluorescein conjugates of concanavalin A (conA) and polylysine were relatively more slowly internalised by macrophages. The half-times for uptake, estimated by fluorescence change, were comparable with the turnover time for bulk plasma membrane. The relatively high average pH experienced by these conjugates indicated that a small proportion of these non-specific cell-surface labels was always in contact with the extracellular medium.

Effect of concanavalin A on lymph node macrophages: stimulation of endocytic cisternae

Incubation of isolated lymph node macrophages with concanavalin A (Con A) resulted in a dense and continuous labeling of the plasmalemma and filopodia which were closely adherent to each other and the cell surface. Within a short time period (3-5 min), membranes of the closely apposed filopodia became invaginated into the cytoplasm to form numerous interconnecting cisternae. After 10 min the system of internalized membranes had migrated into the deeper cytoplasm and was closely associated with numerous actin filaments and other components of the cytoskeleton. The internalized plasmalemma remained in the cytoplasm up to 24 hr without fusing with lysosomes. Concomitant with plasmalemmal invagination and the formation of cisternae there were also changes in the Golgi apparatus. These appeared in the form of hypertrophied Golgi saccules and the accumulation of numerous vesicles around the Golgi. Treatment of isolated lymph node macrophages with either succinylated Con A, alpha-methyl-D-mannoside, or ferritin particles alone failed to produce the cisternal structures. The results suggested that the tetravalency of Con A may be responsible for the binding of adjacent Con A-labeled membranes to each other and for maintaining a crosslinking of membranes during invagination and internalization. It is suggested that this process of extensive membrane internalization represents a specialized form of endocytosis. At 24 hr after incubation with Con A, cisternal structures in close proximity to the Golgi vesicles showed signs of degradation. By 48 hr there was a breakdown of cisternal membranes with a release of Con A marker particles into large phagocytic vesicles, which also showed reaction product for acid phosphatase, suggesting a fusion with lysosomes.

The Legionnaires' disease bacterium (Legionella pneumophila) inhibits phagosome-lysosome fusion in human monocytes

The interactions between the L. pneumophila phagosome and monocyte lysosomes were investigated by prelabeling the lysosomes with thorium dioxide, an electron-opaque colloidal marker, and by acid phosphatase cytochemistry. Phagosomes containing live L. pneumophila did not fuse with secondary lysosomes at 1 h after entry into monocytes or at 4 or 8 h after entry by which time the ribosome-lined L. pneumophila replicative vacuole had formed. In contrast, the majority of phagosomes containing formalin-killed L. pneumophila, live Streptococcus pneumoniae, and live Escherichia coli had fused with secondary lysosomes by 1 h after entry into monocytes. Erythromycin, a potent inhibitor of bacterial protein synthesis, at a concentration that completely inhibits L. pneumophila intracellular multiplication, had no influence on fusion of L. pneumophila phagosomes with secondary lysosomes. However, coating live L. pneumophila with antibody or with antibody and complement partially overcame the inhibition of fusion. Also activating the monocytes promoted fusion of a small proportion of phagosomes containing live L. pneumophila with secondary lysosomes. Acid phosphatase cytochemistry revealed that phagosomes containing live L. pneumophila did not fuse with either primary or secondary lysosomes. In contrast to phagosomes containing live bacteria, the majority of phagosomes containing formalin-killed L. pneumophila were fused with lysosomes by acid phosphatase cytochemistry. The capacity of L. pneumophila to inhibit phagosome-lysosome fusion may be a critical mechanism by which the bacterium resists monocyte microbicidal effects.

The effects of concanavalin A and other agents on protein degradation and migration of non-histone proteins (NHP) to the nucleus in lymphocytes

Concanavalin A (conA) inhibits the degradation of [3H]leucine-labeled cellular proteins of human lymphocytes. The lectin also stimulates the migration of non-histone proteins (NHP) from the cytoplasm to the nucleus. The increased nuclear level of NHP is associated with increased cellular binding of [3H]actinomycin D [(3H]AD). Decreased protein breakdown and increased migration of NHP are parallel events, i.e. both changes occur as a function of the lectin concentration and display a similar time course, suggesting that these events could be related. Similar effects are observed with fluoride, chloroquine and iodoacetate: these agents simultaneously decrease proteolysis and increase the nuclear level of NHP, associated with increased cellular [3H]AD binding. Fractionation of the acidic NHP according to pH 2.5-6.5 shows that proteins with a high degree of degradation in unstimulated cells correspond to proteins with a high degree of migration in conA-stimulated cells. A similar correlation was observed in fluoride-treated lymphocytes. conA, fluoride and iodoacetate decrease cellular [3H]chloroquine [(3H]CQ) accumulation, indicating a lysosomotropic effect. These and previously reported data suggest, but do not prove that conA inhibits degradation of cellular proteins via the lysosomal pathway. Ammonium chloride, methylamine and sodium azide also inhibit proteolysis and increase cellular [3H]AD binding; however, their effects are weak. On the basis of these observations it appears that lysosomal degradation and migration of NHP to the nucleus are linked; however, the mechanism of the linkage is unknown.

Ligand-induced rapid redistribution of lysosomes is temporally distinct from endosome translocation

When many ligands bind to cell-surface receptors, ligand-receptor complexes are internalized via clathrin coated pits by a process called receptor-mediated endocytosis. The cytoplasmic fate of ligands internalized within endocytic vesicles or endosomes is variable. For example, maternal immunoglobulins are transported through the cytoplasm of neonatal intestinal epithelial cells and are exocytosed at the basolateral surface. However, other ligands are degraded as a result of their delivery to the lysosomal compartment of cells. Although the translocation of endosomes to the Golgi region in the cell centre seems to be a general phenomenon presumably coupled to ligand degradation by lysosomes and endosomes and lysosomes undergo saltatory movements within the cytoplasm, the spatial control of interaction between the two structures is not understood. To address this problem we have begun to examine the spatial and temporal intracellular distribution of endosomes and lysosomes. Utilizing a new fluorescent microscopic approach, we have now been able simultaneously to visualize endosome and lysosome populations in living cells. Our results suggest that a specific relocation of lysosomes is rapidly induced upon binding of different types of ligands to the cell surface; this migration of lysosomes to the Golgi region of the cell precedes the translocation of endosomes into the same area.

Concanavalin A binding histiocytes in Hodgkin's disease and their relation to clinicopathologic features of the disease

The occurrence and staining patterns of Concanavalin A (Con A) binding histiocytes were studied in diagnostic lymph node specimens of 133 patients with Hodgkin's disease. Varying numbers of Con A binding histiocytes were present in all tumors. Two distinct cytoplasmic staining patterns of the Con A binding histiocytes were noted: diffuse, and a pattern termed "globular" which represents a dense, solitary paranuclear aggregate of binding sites. The diffuse binding pattern was seen in the majority of histiocytes with no apparent nuclear atypia, but was also occasionally seen in Reed-Sternberg cells. Globular binding was present in both benign and malignant-looking histiocytes, including rare Reed-Sternberg cells. Based on the number of histiocytes in which globular binding of Con A (G-cells) was observed, tumors were grouped in the following three categories: Group 1: tumors with large numbers of G-cells (42 cases); Group 2: tumors with a small number of G-cells (16); and Group 3: tumors with rare or no G-cells (75). Tumors with large numbers of G-cells were seen more frequently in patients with disseminated disease than in those with localized (69.0% versus 31.0%; P less than or equal to 0.002), and more often in patients with B-symptoms than in those without (73.8% versus 26.2%; P less than or equal to 0.001). Large numbers of G-cells were present in most tumors of the lymphocyte depletion type (14/16), whereas rare or no G-cells were seen in the majority of the nodular sclerosis type (46/59). These observations suggest that the G-cells may represent an abnormal variant of histiocytes, the occurrence of which is associated with unfavorable clinical and pathologic features of Hodgkin's disease.

Effect of transmethylation-reaction and increased levels of cAMP on superoxide generation of guinea-pig macrophages induced with wheat germ agglutinin and phorbor myristate

Superoxide (O2-) generation of guinea-pig macrophages induced by wheat germ agglutinin (WGA) was suppressed to a great extent by the inhibition of transmethylation with 3'-deazaadenosine. When macrophages were stimulated with phorbor myristate (PMA) instead of WGA, the suppression of O2- generation of macrophages was observed to be slight despite the presence of 3'-deazaadenosine. These results were confirmed under various conditions. Thus the WGA-stimulated O2- generation of macrophages is probably associated with transmethylation, but the PMA-stimulated O2- generation is not. WGA-stimulated O2- generation of macrophages was also inhibited in the presence of dibutyryl cAMP or prostaglandin E2 (PGE2), substances that increase intracellular cAMP, but PMA-stimulated O2- generation was only slightly affected by these compounds. These results suggest that the mechanism for O2- generation of macrophages caused by WGA is different from that for O2- generation caused by PMA.

Lectin-resistant mutants of polarized epithelial cells

Two lectin-resistant mutants derived from Madin Darby canine kidney cells, with constitutive alterations in the asparagine-linked carbohydrate moieties, retained the characteristic structural and functional epithelial polarity of the parental cells. A ricin-resistant cell line was unable to incorporate galactose-sialic acid into glycoproteins and, from the pattern of cross-resistance to other lectins, appears to be different from previously described lines resistant to this lectin: the mutation in a concanavalin A-resistant line results, probably, in the production of defective carbohydrate cores of glycoproteins. In spite of glycosylation defects which result in an increased electrophoretic mobility of many cellular glycoproteins, both mutants retained the typical asymmetric structure of the plasma membrane (microvilli on the apical surface, junctional elements on the basolateral surface), functional tight junctions, and unidirectional active transport of electrolytes and water. These results suggest that glycoproteins with terminal galactose-sialic acid moieties are not critically involved in the development and maintenance of polarity in epithelial cells. The mutant cells, particularly the ricin-resistant line, exhibited, however, morphological and electrophysiological changes which suggest a quantitative effect of the mutations on intracellular traffic of membranes and tight junction formation. The cell lines described in this paper, the first lectin-resistant mutants of epithelial lineage, should prove useful tools for studying the peculiarities of glycosylating pathways in polarized cells.