Soluble human lymphocyte sugar binding proteins with immunosuppressive activity

Suppression of the immune response, which involves suppressor factors released from specialized T cells, is inhibited by alpha-L-rhamnose. In this paper, we show the presence of rhamnose-specific receptors on a human CD8+ T cell-rich population and describe a novel method to isolate cells which express a given sugar-binding protein on their surface. We describe the isolation of alpha-L-rhamnose-specific molecules (rhamnose-binding fractions: RBF) from a water-soluble extract from lymphocytes, their purification by affinity chromatography on immobilized neoglycoproteins containing rhamnose residues. RBF kept their ability to bind rhamnose, as shown by the binding of fluorescein-labeled RBF to rhamnosylated BSA-substituted beads. RBF efficiently suppresses DNA synthesis of mitogen-stimulated human lymphocytes as well as B cell immunoglobulin production. Therefore, these rhamnose-binding molecules appear to be antigen-independent suppressor factors.

Hydrosoluble fluorogenic substrates for plasmin

New hydrosoluble fluorogenic substrates for plasmin gluconoylpeptidyl-3-amido-9-ethylcarbazole were synthesized. The substitution of the N-terminal end of the peptides by a gluconoyl group prevents the substrates from aminopeptidase degradation and highly increases their hydrosolubility. The substitution of the peptide C-terminal end by a 3-amino-9-ethylcarbazole group leads to substrates suitable for direct fluorometric assay of plasmin present in cell supernatants or in cell lysates. On the basis of the kinetic parameters of the substrate hydrolysis by plasmin, it was found that D amino acids in the P2 position decrease systematically the kinetic constants of the substrates. The L configuration of the P2 amino acid appears therefore as essential in optimum substrates for plasmin.

Human keratinocyte membrane lectins: characterization and modulation of their expression by cytokines

In an attempt to identify cell surface molecules involved in recognition phenomena between cells such as keratinocytes and melanocytes and putatively target biological responses modifiers to keratinocytes, we undertook the detection of cell surface sugar specific receptors: membrane lectins. Keratinocyte membrane lectins were found to bind synthetic glycoproteins (neoglycoproteins) carrying either alpha-L-fucosyl or alpha-L-rhamnosyl residues. Fluorescence microscopy observations indicate that cultured keratinocytes are able to bind these two neoglycoproteins while frozen sections of human skin labelled with neoglycoprotein-coated covaspheres show that the selectivity of the binding to keratinocytes is restricted to alpha-L-rhamnosyl-BSA. Keratinocytes were adapted to grow on collagen; harvesting conditions allowing the analysis of keratinocytes by flow cytometry are described. This technique allows the quantification of the binding at 4 degrees C, and the estimation of the endocytosis of F-, neoglycoproteins: F-, alpha-L-Rha-BSA and F-, alpha-L-Fuc-BSA were efficiently internalized. Thereafter, alpha-L-rhamnose-substituted liposomes containing 5-(6)carboxyfluorescein were prepared in order to follow the delivery of the fluorescent dye into cells. This was measured both by flow cytometry and by spectrofluorimetry. The expression of surface lectins was checked upon action of cytokines (IL1 alpha, IL1 beta, IL2 and TNF) which are known as biological response modifiers of keratinocytes.

Production of macrophage-derived cytotoxic factor by N-[3-[(carbamoylmethyl)thio]propionylated] neoglycoproteins

6-Phosphomannosylated bovine serum albumin (Man6P-BSA), a neoglycoprotein endocytosed by macrophages, bearing either 3-(2-pyridyldithio)propionyl or 3-[(carbamoylmethyl)thio]propionyl residues coming from alkylation of thiol residues by iodoacetamide were prepared and tested for their immunomodulator properties. The supernatants of mouse peritoneal macrophages incubated with Man6P-BSA bearing 3-[(carbamoylmethyl)thio]propionyl groups, and by a lesser extent 3-(2-pyridyldithio)propionyl groups, were cytotoxic to L929 cells, suggesting the presence of a tumor necrosis factor like compound. This macrophage-activation process is linked to the capacity of Man6P-BSA to be endocytosed via membrane lectins of macrophages, because the supernatants of macrophages incubated with unglycosylated conjugates were not cytotoxic. The cytotoxic activity induced by 3-[(carbamoylmethyl)thio]propionyl groups bound onto Man6P-BSA was similar to that induced by Man6P-BSA bearing muramyl dipeptide, indicating that endocytosed neoglycoproteins bearing 3-[(carbamoylmethyl)thio]propionyl residues are potent macrophage activators.

Analysis of nuclear sugar-binding components in undifferentiated and in vitro differentiated human promyelocytic leukemia cells (HL60)

The nuclear sugar-binding components (i.e., lectin-like molecules) were analyzed using isolated and membrane-depleted nuclei after incubation in the presence of fluorescein-labeled neoglycoproteins. This analysis was performed before and during the in vitro differentiation of HL60 cells into monocytes by PMA treatment and into granulocytes by DMSO treatment. The nucleoli of undifferentiated and differentiated HL60 cells were not labeled, unlike the nucleoli of other mammalian cells studied so far. This peculiarity allowed us to quantitatively analyze by flow cytometry the changes in the lectin activity associated with the extranucleolar territories enriched in ribonucleoprotein complexes. The neoglycoprotein binding was found to be significantly lower in differentiated than in undifferentiated cells. The decrease in neoglycoprotein binding was observed within the first 24 h of DMSO or PMA treatment, just before the arrest of DNA synthesis. Taking into account that the granulocytic differentiation required 72 h of chemical treatment, the extra-nucleolar lectins might be involved in modulation of the DNA synthesis rather than in phenotypic differentiation. These data are discussed in an attempt to reconcile the association of lectins with RNP complexes and their possible involvement in modulation of HL60 cell proliferation.

Cell surface lectins of human granulocytes: their expression is modulated by mononuclear cells and granulocyte/macrophage colony-stimulating factor

This paper presents the characterization of a sugar-specific receptor on the surface of human circulating polymorphonuclear cells. With the help of fluorescent neoglycoproteins and flow cytometry, a receptor was identified as being specific for alpha-L-rhamnosyl residues. The number of receptors was 55,000/cell and their affinity reached 2 x 10(8) l mol-1. This number changed as a function of the biological state of the cells. Indeed, receptor expression was modulated by the presence of other cells. T cells and B cells increased the number of receptors on the granulocyte surface. Expression of the alpha-L-rhamnose-specific lectin was dependent on lymphocyte derived soluble factor(s), which induce(s) growth and differentiation of polymorphonuclear phagocytes. Granulocyte/macrophage colony-stimulating factor (GM-CSF) specifically produced a significant increase in the number of receptors for alpha-L-rhamnose (2-10-fold/cell). This modulation was independent of protein kinase C activators such as phorbol ester, which produced no effect on alpha-L-rhamnose receptor expression. These findings demonstrate that GM-CSF may stimulate post differentiation functions and properties of mature granulocytes.

Psi[CH2O] pseudodipeptide synthesis. An improved approach which allows absolute configuration determination

An improved way to obtain psi[CH2O] pseudodipeptide units is proposed, involving an intramolecular Williamson's reaction, with displacement of bromine by an alkoxide, instead of the classical intermolecular one. Until now, psi[CH2O] pseudodipeptide synthesis done by this new method, has used a protected form of the amino alcohol hydroxyl group to prepare the acyclic precursor. In the present paper, the use of an active ester of the brominated carboxylic acid avoids this protection step. The pseudodipeptides AcGly psi[CH2O]-D,L-Ala-OH and Ac-Ser(Bzl) psi [CH2O]-D,L-Ala-OH were obtained in high yields, through a delta-lactam intermediate, which furthermore allows the determination of the absolute configuration of compounds using HPLC and appropriate nuclear magnetic resonance (NMR) techniques.

Drug targeting: anti-HSV-1 activity of mannosylated polymer-bound 9-(2-phosphonylmethoxyethyl)adenine

The antiviral drug, 9-(2-phosphonylmethoxyethyl) adenine (PMEA) was linked to a synthetic and neutral polymer bearing mannosyl residues to allow its internalization by macrophages via membrane lectins. PMEA bound to the mannosylated polymer was more efficient in vitro than free PMEA in preventing lysis of human macrophages by herpes virus.

Endocytosis mediated by monocyte and macrophage membrane lectins--application to antiviral drug targeting

Sugar receptors, or membrane lectins, have been evidenced at the surface of various normal and tumour cells using fluoresceinylated neoglycoproteins (glycosylated bovine serum albumin (BSA]. By flow cytometry we have shown that macrophages bind and internalize mannosylated and 6-phosphomannosylated ligands in acidic compartments. Freshly isolated monocytes and U937, a promonocytic cell line, lack a mannose-specific receptor, but express mannose-6-phosphate (Man-6P) membrane lectin. Neoglycoproteins are potent drug carriers: muramyl dipeptide (MDP), an immunoactivator, when bound to Man-BSA or Man-6P-BSA, is 100 times more efficient than free MDP in activating macrophages; in vivo, it enables eradication of lung metastases in mice. Recently, neutral glycosylated biodegradable and nonimmunogenic polymers, were synthesized and found to be as efficient as neoglycoproteins. Antiviral drug conjugates were more active than the free drug, inhibiting the multiplication of virus (herpes) in human macrophages in vitro.

Macrophage activation by muramyl dipeptide bound to neoglycoproteins and glycosylated polymers: cytotoxic factor production

Some biological functions of macrophages can be stimulated by muramyl dipeptide (MDP) in vitro. Such stimulation is more efficient when MDP is bound to macromolecule carriers. The macrophage stimulation by MDP bound to glycosylated serum albumin (BSA) or bound to gluconoylated and glycosylated poly-L-lysine (PLK) is investigated. These two types of MDP conjugates are more efficient than free MDP in rendering mouse peritoneal and rat alveolar macrophages cytostatic against various tumor cells. However, the release of mitogenic factor or cytotoxic factor (CF) by activated macrophages varies according to the nature of the carrier (BSA or PLK) and to the nature and content of sugar residues bound to the macromolecule carrier (mannose or 6-phosphomannose). Macrophages activated by MDP bound to glycosylated BSA release mitogenic factor and CF into the medium; anti-recombinant tumor necrosis factor (rTNF) totally inhibits the cytotoxicity of the supernatant. On the contrary, MDP bound to glycosylated PLK induces no secretion of mitogenic factor and a very small amount of CF in the culture medium. The role of CF in the cytostatic activity of activated macrophages is discussed. The released CF is not involved in the cytostatic activity, but TNF-like molecules, expressed at the membrane level, could be implied because anti-rTNF abrogates 40% of the cytostatic activity of the macrophages.

Distribution of sugar-binding sites within interphase nuclei and mitotic chromosomes of a human cell line

Using gold labelled neoglycoproteins containing either alpha-D-glucose, N-acetyl-beta-D-glucosamine, alpha-D-mannose, 6-phospho-alpha-D-mannose, and alpha-L-fucose (BSA), we investigated their intranuclear binding sites in the TG human cell line. Although gold-labelled BSA did not give any noticeable labelling, the presence of 1% free BSA in the medium containing the gold labelled neoglycoproteins was revealed to be a key factor of the labelling. During interphase in the presence of free BSA most of the labelling was detected in the nucleoplasm. The border of the condensed chromatin, known to be the site of hnRNA synthesis as well as the interchromatin areas enriched in RNPs were labelled. Condensed chromatin also contained binding-sites. The nucleolus was seen to present low labelling in comparison with the labelling observed over the nucleoplasm. These nucleolar binding sites were located both in the dense fibrillar and granular components. No labelling could be detected over the fibrillar centers which are very conspicuous in this cell line. During mitosis sugar-binding sites were observed over the chromosomes. Data reported here show for the first time that lectin-like proteins and chromatin components are colocalized both during interphase and mitosis. In addition, within the nucleolus the presence of sugar-binding proteins was seen to be restricted to the dense fibrillar and granular components.

Benzoxazinone kanamycin A conjugate. A new fluorescent probe suitable to detect mycoplasmas in cell culture

The synthesis of a new benzoxazinone derivative suitable to detect early infection of cultured cells with mycoplasmas is described. p-[beta-(7-dimethylamino 1,4-benzoxazin 2-one 3yl)-vinyl]- phenylpropenoic acid was coupled to kanamycin A, an aminoglycoside leading to a cationic fluorescent probe which fluoresces at 600 nm upon excitation at 490 nm. This fluorescent probe is shown to heavily label the glycocallix of all the mycoplasma strains tested which are found to be associated with contaminated cultured cells and to allow an easy and rapid detection of contamination by fluorescence microscopy and flow cytometry.

Endocytosis of alpha 1-acid glycoprotein variants and of neoglycoproteins containing mannose derivatives by a mouse hybridoma cell line (2C11-12). Comparison with mouse peritoneal macrophages

Macrophages from various origins are known to express membrane lectins that mediate the endocytosis of mannose-bearing glycoconjugates. Most macrophage tumor cell-lines lack such receptors. In this paper we show by flow cytometry analysis that a newly generated macrophage hybridoma (2C11-12), which displays several macrophage characteristics, also expresses mannose membrane lectins, resulting in the internalization of fluoresceinylated neoglycoproteins into acidic compartments. Thioglycolate elicited mouse peritoneal macrophages and the 2C11-12 hybridomas were compared by flow cytometry with regard to the binding and endocytosis of alpha 1-acid glycoprotein (AGP) variants separated by affinity chromatography on immobilized concanavalin A. AGP C eluted specifically with methyl alpha-mannopyranoside, which contains two bi-antennary oligosaccharides, was endocytosed as mannosylated serum albumin (Man-BSA). In both types of macrophages, the fluoresceinylated ligands were internalized in acidic compartments as demonstrated by the fluorescence intensity increase upon monensin post-incubation. However the behaviour of the internalized ligands was found to be quite different. AGP C and Man-BSA were rapidly degraded by thioglycolate elicited peritoneal macrophages and excreted in the medium as small peptide fragments; conversely they remained a longer time in the 2C11-12 hybridoma.

Macrophage antigens associated with adhesion: identification by a monoclonal antibody specific for Lewis lung carcinoma cells

A monoclonal antibody specific for Lewis lung carcinoma (3LL) cells (Mab 5B5) was found to recognize antigens expressed on murine macrophages and on a macrophage hybridoma line upon cell adhesion on plastic surfaces. These antigens were also present on the surface of murine macrophage tumor M5076 cells which develop solid tumors and metastases. The M5076 tumor cells freshly isolated from the primary tumor and from hepatic metastases strongly bound Mab 5B5 but lost this capacity after adhesion. Freshly isolated thioglycolate-elicited peritoneal mouse macrophages were not labeled by Mab 5B5; however, after 1 h of adhesion, 50% of the adherent macrophages were directly incubated with Mab 5B5 prior to harvesting by scraping. Permeabilization of peritoneal macrophages by saponin showed that the antigens recognized by Mab 5B5 were present inside the cells before adhesion. Similar results were obtained with the 2C11-12 macrophage hybridoma cells. P388D1 cells (a weakly adherent macrophage tumor cell line), HL60 cells (a human promyelocytic cell line), and human monocytes were poorly labeled without permeabilization but were strongly labeled by Mab 5B5 upon permeabilization. The specificity of the monoclonal antibody in relation to the adherence capacity of these cells is discussed.

Muramyl dipeptide bound to poly-L-lysine substituted with mannose and gluconoyl residues as macrophage activators

Poly-L-lysine modified with mannose derivatives, the residual cationic charges of which being neutralized by N-acylation, were synthesized and used as carriers of a macrophage activator (N-acetylmuramyl dipeptide, MDP). The influence of the acylating agent on the targeting efficiency was investigated: a hydrosolubilizing group such as a gluconoyl moiety led to very efficient carrier conjugates, while an acetyl group did not. The effect of sugar and acyl content of the polymers was assessed using these compounds as inhibitors of red blood cell agglutination by Concanavalin A. The binding and specific endocytosis of poly-L-lysine substituted with several mannose derivatives and gluconoyl residues (GlcAx-, Man(y)-PLK) have been determined by a quantitative flow cytometry analysis. MDP bound to these conjugates was much more efficient in vitro than free MDP in macrophage cytostasis assays.

Purification and identification of a neutral endopeptidase in Plasmodium falciparum schizonts and merozoites

An endopeptidase specific to the Plasmodium falciparum erythrocytic schizont stage and to free merozoites was detected using the fluorogenic GlcA-Val-Leu-Gly-Lys(or Arg)-AEC substrate. The enzyme was purified by high performance liquid chromatography (HPLC); its optimal activity was around pH 7.5 and its isoelectric point was 4.4. The molecular weight of the enzyme was about 68,000, as demonstrated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. The endopeptidase was strongly inhibited by thiol proteinase inhibitors, leupeptin, and antipain. The possible involvement of this neutral endopeptidase in the reinvasion process is discussed.

Colorimetric determination of neutral sugars by a resorcinol sulfuric acid micromethod

A microscale colorimetric assay for neutral sugars, in which neutral sugars react with resorcinol in the presence of 75% sulfuric acid solution is described. This assay, based on the use of microtiter plates with 96 U-shaped wells is simple and easy to handle; it allows accurate determinations with small samples (20 microliters) containing 1 to 100 nmol of neutral sugars and is quite convenient for detection of glycoconjugates in chromatographic column effluents.

Characterization and biological implications of membrane lectins in tumor, lymphoid and myeloid cells

Complex carbohydrates and sugar receptors at the surface of eukaryotic cells are involved in recognition phenomena. Membrane lectins have been characterized, using biochemical, biological and cytological methods. Their biological activities have been assessed using labeled glycoproteins or neoglycoproteins. Specific glycoproteins or neoglycoproteins have been used to inhibit their binding capacity in both in vitro and in vivo experiments. In adults, lymphoid and myeloid cells as well as tumor cells grow in a given organ and eventually migrate and home in another organ; these phenomena are known as the homing process or metastasis, respectively. In specific cases, membrane lectins of endothelial cells recognize cell surface glycoconjugates of lymphocytes or tumor cells, while membrane lectins of lymphocytes and of tumor cells recognize glycoconjugates of extracellular matrices or of non-migrating cells. Therefore, membrane lectins are involved in cell-cell recognition phenomena. Membrane lectins are also involved in endocytosis and intracellular traffic of glycoconjugates. This property has been demonstrated not only in hepatocytes, fibroblasts, macrophages and histiocytes but also in tumor cells, monocytes, thyrocytes, etc. Upon endocytosis, membrane lectins are present in endosomes, whose luminal pH rapidly decreases. In cells such as tumor cells or macrophages, endosomes fuse with lysosomes; it is therefore possible to target cytotoxic drugs or activators, by binding them to specific glycoconjugates or neoglycoproteins through a linkage specifically hydrolyzed by lysosomal enzymes. In cells such as monocytes, the delivery of glycoconjugates to lysosomes is not active; in this case, it would be preferable to use an acid-labile linkage. Cell surface membrane lectins are developmentally regulated; they are present at given stages of differentiation and of malignant transformation. Cell surface membrane lectins usually bind glycoconjugates at neutral pH but not in acidic medium: their ligand is released in acidic specialized organelles; the internalized ligand may be then delivered into lysosomes, while the membrane lectin is recycled. Some membrane lectins, however, do bind their ligand in relatively acidic medium as in the case of thyrocytes. The presence of cell surface membrane lectins which recognize specific sugar moieties opens the way to interesting applications: for instance, isolation of cell subpopulations such as human suppressor T cells, targeting of anti-tumor or anti-viral drugs, targeting of immunomodulators or biological response modifiers.

Visualization of exocellular lectins in the entomopathogenic fungus Conidiobolus obscurus

We demonstrated the presence of lectins binding to glucose and N-acetylglucosamine on the surface of Conidiobolus obscurus spores by using glycosylated serum albumins substituted with fluorescent dyes and colloidal gold. The role of these exocellular lectins was examined in relation to the adhesion of the fungal spores to their host insect and the pathogenicity of the fungus.

p-Benzylthiocarbamoyl-aspartyl-daunorubicin-substituted polytrisacryl. A new drug acid-labile arm-carrier conjugate

A new type of drug acid-labile arm-carrier is described. A hydrophilic polymer [polytrisacryl, or poly(acryloyl 2-amido-2-hydroxymethyl-1,3-propanediol)], used as a model, is substituted with p-nitrobenzyl groups. The nitrobenzyl groups are reduced to aminobenzyl and transformed into benzylisothiocyanate groups which are allowed to react with aminoacyl daunorubicin. The excess of benzylisothiocyanate is transformed into benzylthiocarbamoyl N-methyl glucamine. A conjugate containing benzylthiocarbamoyl-aspartyl daunorubicin is stable at neutral pH, and releases free daunorubicin when it is exposed to pH 5 or below. This conjugate is about 200-fold less toxic than free daunorubicin, on a molecular basis, when it is added to the medium of Lewis lung carcinoma (3LL) cells in culture.

Kluyveromyces bulgaricus yeast lectins. Isolation of N-acetylglucosamine and galactose-specific lectins: their relation with flocculation

Kluyveromyces bulgaricus is a yeast which, upon culture in a calcium-enriched glucose-peptone medium, flocculates. Its flocculation can be reversed by the addition of galactose. In this paper, it is shown that two lectins can be isolated either from the concentrated culture broth or from the supernatant of deflocculated cells suspended in galactose solution. The N-acetylglucosamine-specific lectin, at pH 7.4, agglutinates untreated sheep red blood cells, but agglutinates neither untreated rabbit red blood cells nor glutaraldehyde-fixed sheep or rabbit red blood cells. Conversely, at pH 4.5, this lectin agglutinates glutaraldehyde-fixed sheep red blood cells. The galactose-specific lectin, at pH 7.4, agglutinates both untreated and glutaraldehyde-fixed rabbit red blood cells but does not agglutinate untreated or glutaraldehyde-fixed sheep red blood cells. At pH 4.5, this lectin agglutinates both glutaraldehyde-fixed sheep and rabbit red blood cells and induces flocculation of deflocculated K. bulgaricus cells. In all cases, the agglutination and the flocculation induced by one of these two lectins were inhibited by free or conjugated N-acetyl-D-glucosamine or by free or conjugated D-galactose, respectively. No glycosylhydrolase activity could be detected in the purified lectins.