Carbohydrate-containing Antigens Research Articles

Orientationally Fabricated Zwitterionic Molecularly Imprinted Nanocavities for Highly Sensitive Glycoprotein Recognition.

Glycoprotein recognition has recently gained a lot of attention, since glycoproteins play important roles in a diverse range of biological processes. Robustly synthesized glycoprotein receptors, such as molecularly imprinted polymers (MIPs), which can be easily and sustainably handled, are highly attractive as antibody substitutes because of the difficulty in obtaining high-affinity antibodies specific for carbohydrate-containing antigens. Herein, molecularly imprinted nanocavities for glycoproteins have been fabricated via a bottom-up molecular imprinting approach using surface-initiated atom transfer radical polymerization (SI-ATRP). As a model glycoprotein, ovalbumin was immobilized in a specific orientation onto a surface plasmon resonance sensor chip by forming a conventional cyclic diester between boronic acid and cis-diol. Biocompatible polymer matrices were formed around the template molecule, ovalbumin, using SI-ATRP via a hydrophilic comonomer, 2-methacryloyloxyethyl phosphorylcholine, in the presence of pyrrolidyl acrylate (PyA), a functional monomer capable of electrostatically interacting with ovalbumin. The removal of ovalbumin left MIPs with binding cavities containing boronic acid and PyA residues located at suitable positions for specifically binding ovalbumin. Careful analysis revealed that strict control over the polymer significantly improved sensitivity and selectivity for ovalbumin recognition, with a limit of detection of 6.41 ng/mL. Successful detection of ovalbumin in an egg white matrix was demonstrated to confirm the practical utility of this approach. Thus, this strategy of using a polymer-based recognition of a glycoprotein through molecularly imprinted nanocavities precisely prepared using a bottom-up approach provides a potentially powerful approach for detection of other glycoproteins.

Microbial carbohydrate depolymerization by antigen-presenting cells: Deamination prior to presentation by the MHCII pathway

After uptake by the endosome of an antigen-presenting cell (APC), exogenous proteins are known to be degraded into peptides by protease digestion. Here, we report the mechanism by which pure carbohydrates can be depolymerized within APC endosomes/lysosomes by nitric oxide (NO)-derived reactive nitrogen species (RNSs) and/or superoxide-derived reactive oxygen species (ROSs). Earlier studies showed that depolymerization of polysaccharide A (PSA) from Bacteroides fragilis in the endosome depends on the APC's having an intact inducible nitric oxide synthase (iNOS) gene; the chemical mechanism underlying depolymerization of a carbohydrate within the endosome/lysosome is described here. Examining the ability of the major RNSs to degrade PSA, we determined that deamination is the predominant mechanism for PSA processing in APCs and is a required step in PSA presentation to CD4(+) T cells by MHCII molecules. Structural characterization of the NO-derived product PSA-NO indicates that partial deaminative depolymerization does not alter the zwitterionic nature of PSA. Unlike native PSA, PSA-NO is presented by iNOS-deficient APCs to induce CD4(+) T cell proliferation. Furthermore, metabolically active APCs are required for PSA-NO presentation. In contrast to PSA degradation by RNSs, dextran depolymerization in the endosome depends on ROSs, including hydrogen peroxide- and superoxide-derived ROSs. This study provides evidence that MHCII pathway-mediated carbohydrate antigen processing in APCs is achieved by chemical reactions. RNSs and ROSs may be involved in the presentation of glycopeptides by MHC molecules via the processing of other carbohydrate-containing antigens, such as bacterial or viral glycoproteins or glycoconjugate vaccines.

Immune-Mediated Hemolytic Anemia

Hemolytic anemia due to immune function is one of the major causes of acquired hemolytic anemia. In recent years, as more is known about the immune system, these entities have become better understood and their treatment improved. In this section, we will discuss three areas in which this progress has been apparent. In Section I, Dr. Peter Hillmen outlines the recent findings in the pathogenesis of paroxysmal nocturnal hemoglobinuria (PNH), relating the biochemical defect (the lack of glycosylphosphatidylinositol [GPI]-linked proteins on the cell surface) to the clinical manifestations, particularly hemolysis (and its effects) and thrombosis. He discusses the pathogenesis of the disorder in the face of marrow dysfunction insofar as it is known. His major emphasis is on innovative therapies that are designed to decrease the effectiveness of complement activation, since the lack of cellular modulation of this system is the primary cause of the pathology of the disease. He recounts his considerable experience with a humanized monoclonal antibody against C5, which has a remarkable effect in controlling the manifestations of the disease. Other means of controlling the action of complement include replacing the missing modulatory proteins on the cell surface; these studies are not as developed as the former agent. In Section II, Dr. Alan Schreiber describes the biochemistry, genetics, and function of the Fc gamma receptors and their role in the pathobiology of autoimmune hemolytic anemia and idiopathic thrombocytopenic purpura due to IgG antibodies. He outlines the complex varieties of these molecules, showing how they vary in genetic origin and in function. These variations can be related to three-dimensional topography, which is known in some detail. Liganding IgG results in the transduction of a signal through the tyrosine-based activation motif and Syk signaling. The role of these receptors in the pathogenesis of hematological diseases due to IgG antibodies is outlined and the potential of therapy of these diseases by regulation of these receptors is discussed. In Section III, Dr. Wendell Rosse discusses the forms of autoimmune hemolytic anemia characterized by antibodies that react preferentially in the cold-cold agglutinin disease and paroxysmal cold hemoglobinuria (PCH). The former is due to IgM antibodies with a common but particular structure that reacts primarily with carbohydrate or carbohydrate-containing antigens, an interaction that is diminished at body temperature. PCH is a less common but probably underdiagnosed illness due to an IgG antibody reacting with a carbohydrate antigen; improved techniques for the diagnosis of PCH are described. Therapy for the two disorders differs somewhat because of the differences in isotype of the antibody. Since the hemolysis in both is primarily due to complement activation, the potential role of its control, as by the monoclonal antibody described by Dr. Hillmen, is discussed.

Leishmania braziliensis: isolation of carbohydrate-containing antigen and possibility of its use in the immunodiagnosis of American cutaneous leishmaniasis.

Leishmania braziliensis is a causative agent of American Cutaneous Leishmaniasis (ACL). The 034-JCG strain, isolated from a patient from the northern region of Paraná State, Brazil, was cultivated in Blood Agar Base medium, lyophilized and submitted to phenol-water extraction. The extract was treated with RNase I. The carbohydrate containing-antigen (Ag-CHO) was immunogenic to rabbits and showed at least a fraction with some negative charge at pH 8.2. This antigen showed cross-reactivity with the phenol-water extract of the growth medium used for the culture of promastigotes and with the surface antigens of promastigotes. Its composition is: 24.3% of total sugars, from which 11.2% of galactose, 7.5% of mannose and 5.6% of ribose. Protein content was 5.4% and phosphate 18.5%. The antigenic activity was maintained after: repeated freezing-thawing; lyophilization; heating at 100 degrees C for 30 minutes; treatment with RNase, trichloroacetic acid and sodium metaperiodate. The precipitin line obtained is Periodic Acid Schiff positive. The application of the Ag-CHO in counterimmunoelectrophoresis reaction for the immunodiagnosis of ACL showed 60% sensitivity, and no cross-reaction with the five sera of Chagas' disease patients tested. The use of this antigen in a more sensitive technique, with more samples of sera, may improve these results.

A combined chemical and enzymatic strategy for the construction of carbohydrate-containing antigen core units

Glycosidase-mediated coupling of glycal acceptors with galactose donors affords β 1,3-linked disaccharides that are versatile intermediates for further chemical and enzymatic manipulation. The utility of these disaccharides is demonstrated by the elaboration of these compounds into the type I and type IV core disaccharides of carbohydrate-containing antigens. Further conversion of the type IV disaccharide to a mucin-type trisaccharide (Galβ1,6(GlcNAcβ1,6)GalNAc) was accomplished with the use of a β1,6-N-acetylglucosaminyltransferase

Structure of Mycobacteria: Recent Developments in Defining Cell Wall Carbohydrates and Proteins

Work from this laboratory on the immunogens of Mycobacterium species has focused on those based on carbohydrates (with a view to the development of specific tools for the serodiagnosis of mycobacterioses) and on the cell-wall proteins, as a source of protective immunity and as a means of observing specific delayed-type hypersensitivity. Most mycobacteria are endowed with specific, highly antigenic glycolipids that are powerful for the serodiagnosis of individual mycobacterial infections: e.g., the phenolic glycolipids of Mycobacterium leprae and Mycobacterium bovis, the glycopeptidolipids of the Mycobacterium avium complex, and the acylated trehalose-containing lipooligosaccharides of species such as Mycobacterium kansasii, Mycobacterium szulgai, and Mycobacterium malmoense. A search for analogous structures in Mycobacterium tuberculosis has revealed an antigenic diglycosyl diacylglycerol and the immunogenic phosphomannoinositides. Others have reported on the presence of a novel phenolic glycolipid in the Canetti strain of M. tuberculosis. The dominant carbohydrate-containing antigen of M. tuberculosis (responsible for the high-titer anti-arabinofuranosyl activity in tuberculous sera) is lipoarabinomannan, which has been purified in the native state from M. tuberculosis and shown to contain both phosphatidylinositol and phosphoinositol side-branches. The cell wall of M. tuberculosis--more precisely, the peptidoglycan skeleton--is a source of a few distinct, highly immunogenic protein antigens. The recognition, isolation, and characterization of these antigens will also be described.

Characterization of antigenic determinants in histoplasmin that stimulate Histoplasma capsulatum-reactive T cells in vitro

Although antigen-reactive T lymphocytes play a central role in the host response to Histoplasma capsulatum, little is known of the nature of Histoplasma antigens recognized by these cells in vitro. Employing a murine T-cell line and two clones that are reactive with histoplasmin, we examined whether activation of T cells by histoplasmin required the presence of carbohydrate or protein moieties. The approach taken was to modify carbohydrate or protein molecules in histoplasmin by chemical or enzymatic digestion or by lectin adsorption. In parallel, antigen was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis to correlate alterations in functional activity with changes in the electrophoretic appearance of histoplasmin. Treatment of histoplasmin with periodate (0.1 M, 0.05 M, and 0.01 M) or with the endoglycosidases N-glycanase and endoglycosidase H sharply diminished the capacity of histoplasmin to trigger responses by T cells. Reactivity of T cells to histoplasmin that had been adsorbed with lectins binding mannose, glucose, or galactose was reduced by greater than 70%; conversely, the responses by T cells to antigen that had been adsorbed with lectins specific for fucose, N-acetylgalactosamine, or N-acetylglucosamine ranged from 82 to 91% of that to control antigen. Proliferative responses by T cells to histoplasmin that had been digested with chymotrypsin, protease, or trypsin were 2 to 43% of control values. The electrophoretic appearance of histoplasmin was modified by some but not all of the treatments. Partially purified H and M antigens triggered proliferation of T cells. Thus, both carbohydrates and proteins must be present to induce optimal responses by T cells. A portion of the carbohydrates is N linked to proteins, and alpha-D-mannose (or alpha-D-glucose) and beta-D-galactose are the sugar ligands of carbohydrate-containing antigens.

A comparison of use of carbohydrate, cell structure, and toxin formation in naturally occurring and thymine-requiring Staphylococcus aureus strains.

Among a number of carbohydrates studied, glucose, fructose, and sucrose were found to support adequate growth in five Staphylococcus aureus strains selected for their different properties: toxinogenic Wood 46, auxotrophic Wood 46 thy−, encapsulated Smith, penicillin-resistant Saskatchewan 755, and non-toxinogenic and coagulase-negative SA-13.In all these strains, the analog 2-deoxy-D-glucose (deGlc), when included in the culture medium inhibited growth by blocking the use of sucrose or fructose almost completely; D-glucose restored normal growth. A Wood 46 thy− strain was more specifically used to study the effects of deGlc on "balanced and unbalanced" growth and formation of toxin. When added at the beginning of the logarithmic phase of growth in the presence of thymine, deGlc lowered the growth rate of the cells; on the other hand, as expected, penicillin (affecting formation of cell wall and used here for comparison purposes) had a truly killing effect. Thymineless death associated with "unbalanced" growth was inhibited by deGlc and this inhibition was not significantly reversed by glucose. The cells were observed under the fluorescence microscope, after staining with conjugates of rhodamine and lysozyme, as well as with those of fluorescein and anti-Staphylococcus aureus rabbit serum. When grown in the presence of deGlc, the cells were seen as unevenly stained fluorescent dots, while some of those treated with penicillin or undergoing thymineless death appeared as large and amorphous fluorescent bodies, unlike the untreated cells; such changes due to deGlc or penicillin could possibly involve carbohydrate-containing antigens (e.g., mucopeptide and teichoic acid). The results obtained with the use of various standard techniques to detect toxin indicated that toxin formation is inhibited by deGlc, apparently not selectively but proportionately with growth.

NITROGEN-CONTAINING AND CARBOHYDRATE-CONTAINING ANTIGEN FROM ACTINOMYCES BOVIS.

Pirtle, E. C. (National Animal Disease Laboratory, Ames, Iowa), P. A. Rebers, and W. W. Weigel. Nitrogen-containing and carbohydrate-containing antigen from Actinomyces bovis. J. Bacteriol. 89:880-888. 1965.-Water-soluble, heat-stable antigens have been isolated from the supernatant fluids of broth cultures of Actinomyces bovis ATCC 10048 after 8 days of growth in a broth medium composed of Casamino Acids, yeast extract, Tween 80 (polyoxyethylene sorbitan monooleate), sodium thioglycolate, dextrose, and sodium chloride. The antigens were precipitated from the culture supernatant fluid with alcohol and purified by fractional precipitation with alcohol in the presence of calcium or zinc and by chromatography on diethylaminoethyl Sephadex. Two serologically active substances which differed in chemical composition and size were characterized. The larger one contained 71% hexose and 2.8% nitrogen, and the smaller one contained 45% hexose and 5.4% nitrogen. Heterogeneity of these fractions could not be demonstrated by electrophoresis in free solution at pH 7.8 or 2, by ultracentrifugal analysis, by double diffusion in agar, or by immunoelectrophoresis. Despite their differences in chemical composition and size, they appeared identical in activity as antigens in complement fixation and in double-diffusion tests in agar. Each was found to contain mannose as its chief component after hydrolysis and paper chromatography with three solvent systems. A small percentage of the total nitrogen may be attributed to the presence of amino sugars but the remainder is as yet unidentified.