Sialic acid and the social behaviour of cells

On the ultrastructural localization of cell surface sialyl residues versus anionic sites

Membrane-associated sialic acids(SA) are considered to have an important role in a variety of cell sur ace interactions. Visualization of SA sites and their ultrastructural quantitative evaluation have heverally been based on the coulombic interaction between anionic sites of sialyl carboxyl groups with polycationic,electron dense markers, e.g. colloidal ferric hydroxide or cationized ferritin(CF). We have recently demonstrated an alternative method, whereby periodate-induced biotinylation (PIB) of unfixed cells can be used for specific localization of SA in thin sections by ferritin-conjugated avidin (FAv). It was further shown that PIB does not affect the surface anionic charge, since the latter is still available to CF-staining. In order to determine the role of anionic sites on the distribution and configuration of cell surface sialoglycoproteins and or sialoglycolipids, we have compared the topographic distribution of attached FAv or CF particles on normal and pathological blood cells,following successive treatment with sodium periodate and biotin hydrazide.

Sialic Acid: its importance to platelet function in health and disease

Platelets are known to contain sialic acid, most of which resides on glycoprotein carbohydrate side-chains. A large proportion of the platelet sialic acid is neuraminidase-labile. The sialic acid of human platelets is of the N-acetyl neuramininic acid type and is implicated in platelet functional events, such as aggregation and adhesion as well as contributing to the platelet's electrophoretic mobility. In this respect the platelet has an overall electronegative charge which is predominately the result of the carboxyl group of the sialic acid moiety. Platelet subpopulations have been isolated with differing amounts of sialic acid and cleavage of platelet sialic acid by neuraminidase is associated with loss of platelets from the circulation. This has relevance to platelet aging in vivo where removal of platelet sialic acid may reveal 'senescence antigens' which could facilitate platelet 'uptake' by the reticuloendothelial system. The importance of platelet sialic acid status has been described in certain platelet disorders such as some thrombocytopenias as well as particular disease states including malignancies and atherosclerosis.

Targeting normal and neoplastic tissues in the rat jejunum and colon with boronated, cationic acrylamide copolymers

A series of boronated cationic copolymers, composed of different ratios of acrylamide, N-acryloyl-3-aminophenylboronic acid and N-acryloyl-diaminoethane (the cationic moiety), were prepared with the intention of localizing boron neutron capture therapy (BNCT) in experimentally induced polyps on the luminal side of the gut of the rat. The goals of this study were to: (a) test the effect of cationization of the boronated copolymers on their uptake by polyps and normal adjacent epithelium; (b) compare the whole rat body distribution of aminophenylboronic acid (APB) and polymeric APB after local application; (c) measure the effect of micro-environmental parameters such as pH, the presence of mucin and cations on the interaction between the APB-copolymers and the epithelium of the rat intestines. Direct analysis of tissue boron levels showed that polymeric APB-uptake was higher in the colonic polyps than in the surrounding normal tissues. Free APB, however, was found in similar quantities in both. When tested in the normal jejunum and colon of the rat, polymeric APB uptake was directly proportional to the molar content of the cationic monomer in the copolymers. The presence of magnesium ions, free boron cationic monomer and mucin interfered with this uptake in a concentration-dependent manner. The uptake was pH-independent at pH 5, 7 and 10. APB accumulation in the colon polyps was inversely proportional to the cationic monomer content in the copolymers, suggesting an increased amount of mucus around the polyps, which probably impeded the electrostatic attachment of the polymer to the malignant tissue. The use polymeric APB for targeting BNCT in perioperative treatment of colorectal carcinoma is suggested, especially in the cases of microscopic residual disease after curative resection.

Escherichia coli bind to urinary bladder epithelium through nonspecific sialic acid mediated adherence

The first step in the bacterial colonization and infection of uropathogenic Escherichia coli is adherence to uroepithelium. Over 80% of all urinary tract infections are caused by E. coli. Uropathogenic E. coli express several adherence factors including type 1 and P fimbriae, which mediate attachment to the uroepithelium through specific binding to different glycoconjugate receptors. We showed that P and type 1 fimbriae are not the sole adhesins on uropathogenic E. coli and sialic acid also mediates nonspecific bacterial adherence of uropathogenic E. coli and urinary bladder epithelium.

Recruitment of murine neutrophils in vivo through endogenous sialidase activity

Upon activation with various noncytokine stimuli, polymorphonuclear leukocytes (PMNs) mobilize intracellular sialidase to the plasma membrane, where the sialidase releases sialic acid from the cell surface. This desialylation enhances PMN adherence, spreading, deformability, and motility, functions critical to diapedesis. We now have examined the role of sialidase activity in PMN adhesion to and migration across the endothelium in vivo. A polyclonal antibody prepared against Clostridium perfringens neuraminidase 1) detected surface expression of sialidase on human PMNs stimulated with IL-8 in vitro and on murine PMNs stimulated in vivo, but not on that of unstimulated cells, 2) recognized proteins in human PMN lysates and granule preparations that were not detected by preimmune antibody, 3) inhibited bacterial neuraminidase and human PMN sialidase activities in vitro, and 4) inhibited both pulmonary leukostasis in mice systemically infused with cobra venom factor and intrapulmonary transendothelial migration of PMNs into the bronchoalveolar compartment of mice intranasally challenged with interleukin-8. We conclude that the chemokine interleukin-8, like other PMN agonists, induces the translocation of sialidase to the PMN surface and that surface expression of this sialidase is a prerequisite to PMN recruitment in vivo. The ability of antibodies raised against a prokaryotic neuraminidase to recognize eukaryotic sialidase extends the concept of the neuraminidase superfamily to mammalian enzymes. Inhibition of mobilized endogenous sialidase may provide a novel strategy for limiting the inflammatory response.

The prognostic importance of fibronectin and sialic acid levels in human pituitary adenomas

In this study, fibronectin and sialic acid levels were determined in human pituitary adenomas. The mean fibronectin and sialic acid levels for human pituitary adenomas were found to be 31.64 +/- 15.82 microgram/mg protein and 21.90 +/- 9.82 microgram/mg protein, respectively, versus 6.30 +/- 2.96 microgram/mg protein and 9.88 +/- 2.81 microgram/mg protein for the normal brain tissues. Fibronectin and sialic acid levels were significantly higher (P < 0.001) in human pituitary adenomas than the normal brain tissues. In human infiltrative and non-infiltrative pituitary adenomas, the mean fibronectin and sialic acid levels were found to be 40.87 +/- 15.90 microgram/mg protein, 27.59 +/- 11.10 microgram/mg protein and 22.40 +/- 9.51 microgram/mg protein, 16.21 +/- 3.20 microgram/mg protein, respectively. Fibronectin and sialic acid levels were slightly elevated (P < 0.05) in human infiltrative pituitary adenomas compared with non-infiltrative adenomas.

Fibronectin and sialic acid levels in human meningiomas and gliomas

In this study, fibronectin and sialic acid levels have been assayed in human meningiomas and gliomas. The mean fibronectin and sialic acid levels for human meningiomas were 22.01 +/- 9.70 micrograms/mg protein and 19.58 +/- 4.89 micrograms/mg protein, respectively, and for human gliomas were 27.30 +/- 13.70 micrograms/mg protein and 25.67 +/- 11.60 micrograms/mg protein, respectively, versus 9.23 +/- 5.40 micrograms/mg protein and 13.50 +/- 4.30 micrograms/mg protein for normal brain tissues. Fibronectin and sialic acid levels were significantly higher in human meningiomas (P < 0.01 and P < 0.05) and gliomas (P < 0.001 and P < 0.01) than control group. Also the mean fibronectin and sialic acid levels were found to be 18.27 +/- 7.08 micrograms/mg protein and 17.04 +/- 6.25 micrograms/mg protein in Grade I-II and 32.60 +/- 15.00 micrograms/mg protein and 29.50 +/- 11.60 micrograms/mg protein in Grade III-IV gliomas, respectively. Fibronectin and sialic acid levels were significantly higher in Grade III-IV gliomas than Grade I-II gliomas (P < 0.05).

Charge dependence of the distribution of contrast agents in rat cerebral ventricles

Previous studies of MRI contrast resulting from the intracerebral administration of several contrast agents have suggested that the distribution of these agents may be dependent on the net charge. In order to further evaluate the significance of this parameter, the distribution of both aquo and CDTA-chelated lanthanide and transition metal ions in the cerebral ventricles of rats has been evaluated based on their enhancement of MRI contrast. The agents were injected directly into the lateral ventricles of Sprague-Dawley rats. Each of five different positively charged paramagnetic metal ions tested selectively enhanced the inner cellular layers of ventricular luminal wall of the rat brain, while such enhancement was absent using the corresponding negatively charged metal-CDTA complexes. The abundance of negatively charged residues on the cell surface of the inner luminal layers is suggested to be the source of the observed charge affinity. Differences in the distribution of Mn2+ ions administered intracerebrally compared with intraperitoneal (ip) injection suggest that while the first treatment may result primarily in uncomplexed aquo ions which then interact with the luminal surface, manganese ions administered ip behave more like chelated ions and are most probably complexed to transferrin.

Mobilization of sialidase from intracellular stores to the surface of human neutrophils and its role in stimulated adhesion responses of these cells

Desialation of cell surfaces has been associated with the initiation or modification of diverse cellular functions. In these studies we have examined the subcellular distribution of sialidase (SE) in human neutrophils as well as the mobilization of this enzyme following neutrophil activation. Separation of subcellular fractions by density gradient centrifugation showed that SE is present not only in neutrophil primary and secondary granule populations, like lysozyme, but also in plasma membrane fractions. Neutrophil activation was associated with a redistribution of SE from secondary granule-enriched fractions to the plasma membrane. Furthermore, SE activity detected on the surface of intact neutrophils with a fluorescent SE substrate increased rapidly after activation with kinetics that matched both the loss of total cell-associated sialic acid and release of free sialic acid from the cells. These activation-dependent events were in each case blocked by incubation of neutrophils with the SE inhibitor, 2-deoxy-N-acetyl-neuraminic acid. Aggregation responses of neutrophils as well as adhesion responses to nylon and plastic surfaces were also inhibited by 2-deoxyNANA. Our findings indicate that the activation-dependent desialation of the neutrophil surface is associated with mobilization of an endogenous SE to the plasma membrane and has a role in stimulated adhesion responses of these cells.

Sialic acid binding lectins

The literature contains several reviews on lectins in general, covering mainly those from plants and invertebrates. However, the sialic acid binding lectins have not been reviewed so far. Considering the importance of sialic acids in cell sociology, lectins which specifically recognize terminal sialic acid residues are potentially useful as analytical tools in studying the biological functions of sialoglycoconjugates. These lectins, along with monoclonal antibodies raised against sialoglycoconjugates, have been used in the detection, affinity purification, cytochemical localization and quantitation of such glycoconjugates. In this review the main emphasis has been placed on the occurrence, general purification procedures, macromolecular properties, sugar specificities and applications of these lectins.

Subcellular localization of sialic acid in human brain tumors

The subcellular localization of sialic acid has been investigated in various types of human brain tumors, such as astrocytoma, meningioma and primary malignant lymphoma. High levels of sialic acid were observed in the microsomal fraction of all types of tumors. However, there was no significant difference between values obtained in meningioma, primary malignant lymphoma, and normal tissue, in the fractions examining nucleus, mitochondria and supernatant.

RISH. VII: Cell surface patterns--association of like cells

Like-cells associate to form various tissues, and it has been demonstrated that this specificity resides in the plasma membrane. Membrane bound tissue specific antigens and enzyme substrate mechanisms have been considered to be involved in this phenomena, but these explanations are incomplete. It is proposed that like-cells identify each other by specific complementary cell-surface patterns. This complementarity results from cell division. That is, when cells divide, they give rise to a mirror image of themselves. These complementary patterns are the result of the association of histocompatibility antigens (HCA) with non-histocompatability components in the plasma membrane. This proposal is based on topographic conjecture in that four colours are sufficient for colouring all maps drawn on a plane or sphere so that regions that share a common boundary are of a different colour. It is further proposed that these specific cell-surface patterns can be classified as four overlapping regions: (i) homotypic--which is generally species specific, (ii) allotypic--which is variable within a species, (iii) idiotypic--which represents variation within an individual or family group, and (iv) embryotypic--which identifies the embryonic origin of the tissue.

General methods for modification of sialic acid at C-9. Synthesis of N-acetyl-9-deoxy-9-fluoroneuraminic acid

Methyl 5-acetamido-3,5-dideoxy-2-O-methyl-D-glycero-D-galacto-2-nonulopyrano sate was converted into the 9-O-trityl derivative and the remaining hydroxyl groups were protected as benzyl ethers. Removal of the trityl group, followed by treatment with diethylaminosulfur trifluoride gave the 9-deoxy-9-fluoro derivative, and deprotection N-acetyl-9-deoxy-9-fluoroneuraminic acid (8). In another procedure, coupling of 2-acetamido-2,6-dideoxy-6-fluoro-D-glucopyranose with potassium di(tert-butyl) oxaloacetate, followed by hydrolysis and decarboxylation gave 8. Some of the derivatives were active as inhibitors of growth of mouse mammary adenocarcinoma (TA3) and L1210 cells in culture.

T-antigen in normal and neoplastic urothelium

The expression of the Thomsen-Friedenreich antigen (T-antigen) in normal and neoplastic urothelium was investigated using paraffin-processed and fresh frozen tissue sections obtained by biopsy from 56 patients. The T-antigen was detected through its binding to the peanut agglutinin (PNA) with two methods: a biotin-avidin-peroxidase system or a modified red cell adherence test. In vitro treatment of the tissue sections with neuraminidase induced PNA binding in the normal and neoplastic urothelium as well as the red blood cells and the vascular endothelium. Spontaneous PNA binding was absent in normal bladder epithelium, but was observed in 10% of the noninvasive and 65% of the invasive transitional cell carcinomas (TCC). The positive reactions were seen in the cytoplasm, cell surface, and mucin. These results were correlated with the light and electron microscopic findings and with the detectability of the A, B, H blood group antigens in the same tissues. Ultrastructurally, the PNA binding sites frequently corresponded to the Golgi apparatus and to secretory products which stained with Alcian blue. About 90% of TCCs with spontaneous PNA binding did not express the expected blood group antigen. The latter was also undetectable in 54% of TCCs lacking spontaneous PNA binding. It appears, therefore, that the expression of T-antigen occurs later in the evolution of aggressive TCCs, usually when they have advanced to invasive stages. The finding of spontaneous T-antigen unmasking correlates with the presence of invasion and a higher risk for metastatic involvement of regional lymph nodes.

Evidence that ruthenium red disturbs the synaptic transmission in the rat hippocampal slices through interacting with sialic acid residues

Ruthenium red (RR) at a concentration of 0.71 mM selectively blocked synaptic transmission in hippocampal slices. Antidromically evoked potentials and fibre potentials were only little affected. The action of RR was reversible by washout, but only following shorter (40-50 min) times of incubation. After longer incubation times (hours), the abolished population spike did not recover after washout but could be restored by facilitation of the calcium transport into the nerve terminal with 3,4-diaminopyridine. Partial liberation of sialic acid with neuraminidase from Vibrio Cholerae markedly increased the time after which the potential was abolished by RR. Exogenously added gangliosides and sialic acid also delayed the action of RR. Calcium at a concentration of 13.2 mM prevented or reduced the RR effect. It is concluded that RR binds to sialic acid residues, interfering with neurotransmission by disturbing the calcium transport into the cell.

Influence of neuraminidase and N-acetylneuraminic acid on basophil histamine release in vitro

Since N-acetylneuraminic acid (NANA) in cell membrane glucocalyx mediates or modulates a variety of actions, such as mediator release, we examined a possible modulating role of this amino sugar in histamine release from human basophil leukocytes. Removal of NANA from the cell membrane by the enzyme neuraminidase caused a dose-dependent histamine release. Removal of smaller amounts of NANA enhanced histamine release induced by anti-IgE, Concanavalin A and the calcium ionophore A23187, and reduced the interval between addition of antigen and initiation of histamine release. Pretreatment with free NANA had the opposite effects, i.e. a diminished and delayed maximal histamine release. The hypothesis that NANA in the cell membrane modulates the cellular response to stimulation was further substantiated by demonstrating that the altered response was reflected by a change in the sensitivity of the cell to extracellular calcium. NANA in the cell membrane glucocalyx thus seems to modulate the basophil response to stimulation by modulating transmembraneous calcium transport.

Serum sialyltransferase and fucosyltransferase activities in patients with multiple myeloma

A significant elevation of serum sialyltransferase and fucosyltransferase mean activities was observed in 19 untreated patients with multiple myeloma. However, sialyltransferase mean activity was significantly lower in 13 other patients treated for 1-30 months with alkylating drugs and prednisolone. Such a definite decrease in serum enzyme activity on treatment was not recorded for fucosyltransferase. Instead, this activity was significantly increased in treated patients as compared to controls. The presenting clinical features of the 32 patients with multiple myeloma were the basis for a clinical staging system with regard to myeloma cell burden according to established criteria. In untreated patients (as opposed to treated ones), a significantly higher serum sialyltransferase (but not fucosyltransferase) activity was obtained among those 11 belonging to stage III than among the other eight with stages I and II, suggesting a link between tumour burden and enzyme activity. This assumption was further strengthened in those six patients followed lengthwise with regard to serum sialyltransferase activity. Concomitantly with objective evidence of change in tumour burden they showed corresponding alterations in sialyltransferase activity. The determination of sialyltransferase and fucosyltransferase activity in serum may be an additional contribution to refine initial assessment and follow-up of individual patients with multiple myeloma.

Effect of poly-L-lysine and neuraminidase on the infectivity of Trypanosoma cruzi in cultured HeLa cells

The percentage of parasitisation and index of adherence of Trypanosoma cruzi has been studied when host HeLa cells or metacyclic forms were pretreated with neuraminidase or with poly-L-lysine. The percentage of parasitisation was significatively reduced (P less than or equal to 0.001) when cells were pretreated with poly-L-lysine while pretreatment with neuraminidase caused no apparent effects. On the other hand, the adherence of the metacyclic forms pretreated with poly-L-lysine or neuraminidase was significantly higher than that of the control group.

Immunoglobulin fragments, F(ab')2, that are cytotoxic to enzyme-treated cells

Bivalent immunoglobulin fragments of IgG, F(ab')2, prepared from normal murine sera were found to be cytotoxic to neuraminidase-treated cells. The fragments were cytotoxic to both allogenic and syngeneic targets (with respect to the source of the sera), suggesting that the antigen bound by the F(ab')2 is not related to the major histocompatibility locus of mice (H-2).

Serum sialyltransferase and fucosyltransferase activities in patients with bronchial carcinoma

Serum sialyltransferases and fucosyltransferases measured by an affinity adsorbent technique were studied in 27 exactly defined patients with malignant pulmonary diseases. Fourteen patients with benign pulmonary diseases and 56 with benign surgical diseases were used as controls. Enzyme activities were expressed as amounts of labeled precursor molecules incorporated into endogenous acceptors in counts per minute (cpm). The mean sialyltransferase activity was 583 cpm in bronchial carcinoma, 485 cpm in benign pulmonary disease and 428 cpm in benign surgical disease. The only statistically significant difference was between bronchial carcinoma and benign surgical disease. The mean fucosyltransferase activity was 813 cpm in bronchial carcinoma, 436 cpm in benign pulmonary disease and 255 cpm in benign surgical disease. All the differences were statistically significant. There were no statistically significant differences between the WHO histologic bronchial carcinoma groups. The correlation between sialyltransferase and fucosyltransferase activity in bronchial carcinoma was statistically significant (r = 0.59). In squamous cell carcinoma (N = 6), it was strongly significant (r = 0.96) and there was a significant correlation also in small cell carcinoma (N = 10; r = 0.79) but not in adenocarcinoma (N = 9; r = 0.30) and benign pulmonary disease (N = 14; r = 0.44). It is suggested that serum sialyltransferases and fucosyl transferases would not be decisive for diagnosis when used alone in bronchial carcinoma, but could be included in a screening test battery.

N-acetyl-D-mannosamine analogues as potential inhibitors of sialic acid biosynthesis

The 1,3,6-tri-O-acetyl and 1,3,6-tri-O-acetyl-4-O-mesyl analogues of N-acetyl-D-mannosamine and the corresponding N-trifluoroacetyl derivative have been synthesized, and their effects on the proliferation of Friend erythroleukemia cells in culture have been evaluated. The acetamido series showed a dependency on the 4-substituent for optimum cytotoxicity while the trifluoroacetamido series did not. Thus, the 1,3,4,6-tetra-O-acetyl and 1,3,6-tri-O-acetyl-4-O-mesyl analogues of N-acetyl-D-mannosamine were 10-fold and 42-fold more active, respectively, than 2-acetamido-1,3,6-tri-O-acetyl-2-deoxy-alpha-D-mannopyranose as inhibitors of cellular replication. The corresponding trifluoroacetamido analogues were essentially equiactive and had a potency equivalent to that of the 4-O-mesyl derivative in the acetamido series.

Adhesion of mouse blastocysts to uterine epithelium in culture: a requirement for mutual surface interactions

Blastocysts readily adhered to inert materials in culture, but they resisted adhesion to living cells even after several days under conditions which encouraged cell aggregation. As far as could be determined by observing their spreading behavior on polylysine- and polyglutamate-coated dishes, the mechanism of adhesion of blastocysts to inert surfaces was similar to that of freshly dissociated cells and cell lines. However, their adhesion to vesicles of isolated uterine epithelium, which was encouraged by hanging drop culture, was by a different mechanism that involved microvilli on both the embryonic and maternal surfaces. This interactive step, which was similar to that seen during attachment in vivo, was followed by a brief period of close trophoblast-epithelial contact which led ultimately to phagocytosis of sloughed epithelium. Blastocysts showed a clear preference for adhesion to cultured epithelium in vesicles that had begun to collapse. In this case the cells showed a columnar profile with sharply defined microvillous apexes, unlike the flattened cells in fully expanded vesicles or on culture dishes. We conclude that the preimplantation adhesion of mouse blastocysts requires specific changes on both the embryonic and maternal surfaces to overcome the mutual nonadhesiveness typical of epithelia. The relatively rapid adhesion of blastocysts to a culture dish, on the other hand, is more typical of the well-known spreading behavior of cells on a highly attractive surface.

Cell surface sialoglycoproteins of cultured rat cerebellar interneurons

The sialoglycoproteins of cultures of relatively pure rat cerebellar interneurons were labelled by NaIO4 oxidation/NaB 3H4 reduction. The labelled molecules were analysed by polyacrylamide gel electrophoresis in sodium dodecyl sulphate followed by fluorography. Faint labelling could be detected in three components if cells were labelled without any oxidation. In young cultures, oxidation by galactose oxidase alone failed to reveal any additional bands. After oxidation by NaIO4 or galactose oxidase in the presence of neuraminidase, many more components were labelled. After NaIO4 oxidation, about 80% of the cell-associated radioactivity could be removed by treating the cells with neuraminidase, which left the cells more than 95% viable. The majority of the bands seen after neuraminidase treatment were substantially reduced when compared with untreated controls, supporting a surface localisation of these molecules. Reproducible developmental changes were seen in the profiles of bands labelled by NaIO4/NaB 3H4 in time course studies of cultures up to 8 days in vitro. Some bands became more prominent, and others disappeared. The gel profiles of the neuron cultures were quite distinct from those of cerebellar astrocyte cultures, which contain all the cell types likely to be contaminants of the neuron cultures.

Cell-type-related segregation of surface galactosyl-containing components at an early developmental stage in hemopoietic bone marrow cells in the rabbit

The avidin-biotin complex was used for the selective ultrastructural labeling of terminal cell surface galactosyl residues. Rabbit bone marrow cells were treated with the enzyme galactose oxidase in the presence of biotin hydrazide. Subsequent treatment with ferritin-avidin conjugates enabled the electron microscopic visualization of terminal membrane-based galactose and/or N-acetylgalactosamine on these cells. All stages of erythroid development were characterized by high levels of exposed cell surface galactose, whereas all leukoid cells in the same preparations were virtually unlabeled by the above method. Modulations in the distribution of these surface determinants during differentiation and maturation of rabbit erythroid cells were found to concur in inverse fashion with respect to that of terminal sialic acids. Neuraminidase treatment, before the above labeling procedure, resulted in the exposure of additional galactosyl residues on the surface of all bone marrow cell types. The results indicate that a galactose-bearing glycoconjugate(s) may comprise an erythroid-specific membrane constituent of rabbit bone marrow cells. The high density of galactose on the surface of even the earliest erythroid precursors may eventually enable the identification and isolation of a stem cell, which already contains the erythroid-specific galactoconjugate(s). The results suggest that variations in the spectrum of cell surface carbohydrates may serve as recognition signals in the complex set of intercellular interactions which occur during the development and maturation of the erythrocyte. The occurrence of similar but species-specific variations in the complement of surface heterosaccharides during erythroid development of humans and other mammals supports this contention.

Indomethacin modulates plasma membrane-associated properties of macrophages

Changes in the plasma membrane of macrophages treated with indomethacin were investigated. A significant decrease in the binding of IgG was observed with indomethacin-treated cells, as compared to the control group. Electron microscopic examination did not show any significant morphological differences between the indomethacin treated macrophages and the controls. It was found, however, that indomethacin treatment resulted in a drastic increase in the binding capacity of the cell membrane to cationized ferritin. It is suggested that indomethacin may have a modulating effect on the macrophage plasma membrane.

Tissue- and developmental stage-specific forms of a neural cell surface antigen linked to differences in glycosylation of a common polypeptide

We have previously identified a cell surface glycoprotein of the mouse nervous system named brain cell surface protein-2 (BSP-2). Here we report that this antigen is not a single, discrete entity, but a family of antigenically and structurally related molecules. Three components of 180, 140, and 120 K were characteristic for more mature nervous tissues. Adult cerebral cortex contained the 140-K and 120-K antigens, adult spinal cord only the 120-K, and dorsal root ganglia from young mice mainly the 180-K component. Very different forms of the antigen that migrated as a diffuse zone from 180-250-K in SDS-polyacrylamide gels were found in immature nervous tissues. A molecule different from the previous ones was found in a neuroblastoma line. Evidence is presented that the structural diversity of BSP-2 is due to differences in glycosylation. This result indicates that cell type- and developmental stage-specific glycoprotein patterns previously found in the nervous system may in part be due to different glycosylation of identical polypeptides. The finding that a neural cell surface protein may be glycosylated in different ways has important implications for the generation of cell surface specificity.

Inhibition of in vitro biosynthesis of N-acetylneuraminic acid by N-acyl- and N-alkyl-2-amino-2-deoxyhexoses

The biosynthesis of N-acetylneuraminic acid is markedly inhibited by 2-deoxy-2-propionamido-D-glucose (GlcNProp) and to a much lesser extent by 2-deoxy-2-propionamido-D-mannose (ManNProp), but not by 2-deoxy-2-propionamido-D-galactose and N-methylated derivatives of 2-amino-2-deoxy-D-glucose. 2-Deoxy-2-trimethylamino-D-glucose is a weak inhibitor of 2-acetamido-2-deoxy-D-mannose metabolism. When incubated in a cell-free system from rat liver, GlcNProp gives the 6-phosphate, which is converted into N-propionylneuraminic acid. Evidence is presented which shows that it is the metabolites GlcNProp-6-P and ManNProp-6-P which are the competitive inhibitors, and not GlcNProp itself.

The reversal immune surveillance hypothesis: part II

The first part of the reversal immune surveillance hypothesis (RISH. I) describes the conceptual framework of the immune system as a homoeostatic mechanism for the control of cell differentiation and replication. The thymic dependent lymphocytes (T-cells) are considered to be tissue specific and identify aberrations in the cell surface pattern (antigens), that represent that particular cell type. The T-cells may then recruit antibody forming B-lymphocytes (B-cells) to produce antibodies (humoral response) to the cell surface antigens in order to return the cell surface pattern to its correct state. The antigens may also be removed from the cell surface as immune complexes by the complement system, which under normal conditions does not cause cell lysis. The cellular arm of the immune system, that of killer cells or activated macrophages are considered to be primarily involved with tissue remodelling. Whether or not the humoral or cellular arm of the immune system is activated depends upon the antigens displayed by the stimulating cell. The proposed system, which is self monitoring, is considered to have evolved from the invertebrates through to the vertebrates to become more complex in the mammals. Therefore the immune system is considered to be based on the identification of self and self-foreignness, rather than on foreignness per se.

Identification of a glycophorin-like molecule at the cell surface of rat thymocytes

There are three predominant glycoproteins in the rat thymocyte plasma membrane. Two of these have carbohydrate compositions that are characteristic of structures N-glycosidically linked to protein. The other glycoprotein is very different, having about 20 O-glycosidically linked carbohydrate units per 100 amino acids. It has similarities to the major sialoglycoprotein of human erythrocytes.

Altered reactivity for A, B, H antigens in transitional cell carcinomas of the urinary bladder. A study of the mechanisms involved

Transitional cell carcinomas (TCCs) of the urinary bladder show variable blood group (BG) antigen reactivity even in the non-invasive stage. A correlation exists between the tumor reactivity and subsequent clinical course: when the expected BG antigen(s) is retained, the clinical course is favorable; absence of the expected antigen(s) denotes an aggressive potential. In the present study we investigated some of the possible mechanisms of altered BG antigen reactivity in TCCs. It was found that the "loss" of A, B, H reactivity is a quantitative phenomenon and the threshold for positive reactions depends on the method of tissue processing and the titer of the antisera. Thus, in the 35 cases studied, paraffin processing resulted in reduced reactivity compared to fresh-frozen tissue sections. The reactivity of tumors that appeared positive when tested with undiluted antisera was found reduced when quantitatively compared to that of normal mucosa from the same individual. Excessive or inappropriate sialylation does not appear to be responsible for the reduced BG antigen reactivity of the tumors. In fact, TCCs (9 cases) had significantly reduced sialic acid content compared to normal bladder mucosae (6 cases) regardless of their A, B, H reactivity and neuraminidase did not change their reactions for BG antigens. In addition, spontaneous unmasking of the Thomsen-Friedenreich (T) antigen was observed in invasive tumors that were negative for the expected BG antigen(s). Tumors from patients of blood group A or B often showed increased reactivity for the H antigen, although their A or B antigen was reduced or absent. In view of the known biosynthetic sequence from H to A and B substances, these observations suggest a specific biochemical defect in the tumors.

Isolation, purification, and properties of neuraminidase from Propionibacterium acnes

Neuraminidase activity was discovered in 32 of 38 strains of Propionibacterium acnes. Enzyme production was studied in yeast extract bouillon of different pH containing various amounts of human milk as neuraminidase inductor. Enzyme activity was found in the bacterial sediments as well as in the culture filtrates. Since neither ultrasonic treatment nor lysozyme incubation of bacterial sediments did release reasonable amounts of enzyme, culture filtrates were used for enzyme preparation. Neuraminidase was isolated by 40% ammonium sulfate precipitation, dialysis, concentration and repeated gel chromatography on Sephadex G-100. The enzyme posesses a molecular weight of about 33 000 and a pH-optimum around 5.0. The Michaelis constants are 1.8 x 10(-3) M for alpha 2 leads to 3 linked N-acetylneuraminic acid (NeuAc) in II3NeuAc-Lac, 3.7 x 10(-3) M for the alpha 2 leads to 6 linkage in II6NeuAc-Lac, and 2.1 x 10(-3) M for the alpha 2 leads to 8 linkage of II3 (comes from 2 alpha NeuAc8)2-Lac, respectively. Among the different groups of naturally occurring NeuAc-containing substrates, i.e. oligosaccharides, glycolipids and glycoproteins, the enzyme exhibits its highest activity towards low molecular weight oligosaccharides. Activity is considerably lower on glycoproteins. Glycolipids (gangliosides) are only little attacked under conditions used in the test. However, there is no remarkable specificity towards one of the different linkage types of N-acetylneuraminic acid. In general, the enzyme reveals a specificity pattern similar to that found in other bacteria of low pathogenicity towards man.

Isolation and characterisation of a sialic acid-binding lectin (carcinoscorpin) from Indian horseshoe crab Carcinoscorpius rotunda cauda

A sialic acid-binding lectin, carcinoscorpin, has been purified to apparent homogeneity in 40% yield from the Indian horseshoe carb, Carcinoscorpius rotunda cauda. This glycoprotein lectin of molecular weight 420,000 was composed of two non-identical subunits of molecular weights 27,000 and 28,000 as determined by gel electrophoresis in the presence of sodium dodecyl sulfate. The hemagglutination activity of the lectin was susceptible to guanidine-HCl; modification of tyrosyl and tryptophanyl residues also inhibited the activity although alkylation of the -SH group, reduction of disulfide bonds or modification of amino and carboxyl groups were without any effect. The monomeric form of the lectin produced by succinylation of native protein was inactive in binding to sialoglycoconjugates.