Duan, J., Avci, F.Y. & Kasper, D.L. Microbial carbohydrate depolymerization by antigen-presenting cells: deamination prior to presentation by the MHCII pathway. Proc. Natl. Acad. Sci. USA 105, 5183-5188

Department of Medicine, Channing Laboratory, Brigham and Women's Hospital and Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 05/2008; 105(13):5183-8. DOI: 10.1073/pnas.0800974105
Source: PubMed


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.

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    • "Next to the DC-SIGN-mediated PSA binding at the molecular level, we show an enhanced binding of PSA to DC-SIGN expressing Raji cells over the parental cell line. Raji cells are frequently used as model for PSA internalization and presentation in MHC class II (Kalka-Moll et al., 2002; Cobb et al., 2004; Cobb and Kasper, 2008; Duan et al., 2008; Ryan et al., 2011). In our assays PSA internalization was also detectable in the parental cell line, however this could only be observed when cells were incubated with high concentrations of PSA. "
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    ABSTRACT: The zwitterionic capsular polysaccharide A (PSA) of Bacteroides fragilis is the first carbohydrate antigen described to be presented in major histocompatibility complex (MHC) class II for the induction of CD4(+) T cell responses. However, the identity of the receptor mediating binding and internalization of PSA in antigen presenting cells remains elusive. C-type lectins are glycan-binding receptors known for their capacity to target ligands for antigen presentation to T cells. Here, we investigated whether C-type lectins were involved in the internalization of PSA and identified dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) as the main receptor for PSA on human dendritic cells (DC). The induction of PSA-specific T cell proliferation appeared to be completely dependent on DC-SIGN. These data reveal a crucial role for DC-SIGN in the endocytosis and routing of PSA in human DC for the efficient stimulation of PSA-specific CD4(+) T cells.
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    • "This property of the PSA depended upon its zwitterionic character. Kasper provided an update of his laboratory's continuing efforts to delineate the molecular events associated with the processing of the zwitterionic PSA and its presentation to T cells [3]. After internalization by APC, the high molecular weight PSA traffics through the endosomal pathway and is subsequently processed into smaller fragments. "
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    • "However, either prolonging treatment of ZPS or dextran with exogenous ROS/RNS or increasing the ROS/RNS concentration results in formation of smaller degraded products in vitro. These data suggested that the ROS/RNS-induced depolymerization of polysaccharide is finely controlled in APCs (Duan et al. 2008). More recently, it has been shown that the oxidation of endocytosed PSA release protons which in turn inhibits the breakdown of PSA. "
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    ABSTRACT: Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are constantly produced and are tightly regulated to maintain a redox balance (or homeostasis) together with antioxidants (e.g. superoxide dismutase and glutathione) under normal physiological circumstances. These ROS/RNS have been shown to be critical for various biological events including signal transduction, aging, apoptosis, and development. Despite the known beneficial effects, an overproduction of ROS/RNS in the cases of receptor-mediated stimulation and disease-induced oxidative stress can inflict severe tissue damage. In particular, these ROS/RNS are capable of degrading macromolecules including proteins, lipids and nucleic acids as well as polysaccharides, and presumably lead to their dysfunction. The purpose of this review is to highlight (1) chemical mechanisms related to cell-free and cell-based depolymerization of polysaccharides initiated by individual oxidative species; (2) the effect of ROS/RNS-mediated depolymerization on the successive cleavage of the glycosidic linkage of polysaccharides by glycoside hydrolases; and (3) the potential biological outcome of ROS/RNS-mediated depolymerization of polysaccharides.
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