![]() Despite the recognition of mono- and disaccharide epitopes, most circulating carbohydrate-specific antibodies bind with low specificity to larger glycoconjugates, thus preventing the occurrence of disseminated antibody-mediated inflammatory reactions and autoimmunity. The repertoires of carbohydrate antigens recognized show a large inter-individual variability among human beings. Antibodies against β4-linked oligosaccharides of Glc, α-Gal and GlcNAc(β1–4)GlcNAc are also commonly observed. These most prominently recognized antigens include the monosaccharides α-rhamnose, α-GlcNAc and β-GlcNAc, and the sulfated Gal(β1–4)GlcNAc structure. Commonly recognized carbohydrate antigensĪ large pool of serum IgM and IgG recognizes a variety of carbohydrate antigens. The multitude of combinations of monosaccharides together with a wide range of glycosidic linkages occurring in prokaryotes and eukaryotes yield an extensive repertoire of carbohydrate antigens susceptible to stimulate the production of antibodies in humans. Accordingly, Glc can be recognized as a foreign antigen and elicit the production of antibodies, when it is polymerized through linkages unused in human cells, such as β1–3 or β1–6 found in fungal and bacterial β-glucans. Beyond monosaccharide composition, carbohydrate conformations and thereby antigenic properties largely depend on the types of glycosidic linkages connecting monosaccharides. In contrast, Fuc is the only deoxyhexose and NeuAc the only sialic acid found on human glycoconjugates. In addition to the ten monosaccharides found on human cells, bacterial glycans contain several deoxysugars and deoxyaminosugars, such as rhamnose, quinovose, N-acetylrhamnosamine and N-acetylquinovosamine, arabinose and 3-deoxy-D-manno-octulosonic acid (KDO). By comparison, bacterial glycosylation is based on an alphabet consisting of more than one hundred distinct monosaccharides. Although human glycoconjugates encompass a tremendous diversity of structures, human glycosylation is based on the combination of only the ten monosaccharides glucose (Glc), galactose (Gal), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), glucuronic acid, iduronic acid, xylose, mannose, fucose (Fuc), and the sialic acid N-acetylneuraminic acid (NeuAc). Carbohydrate antigens eliciting an immune response represent structures consisting of monosaccharides and oligosaccharides that are foreign to the host. Yet, carbohydrate-specific antibodies are widespread among all classes of immunoglobulins. Mimicry between bacterial and human glycoconjugates, however, can also lead to the generation of carbohydrate-specific antibodies that cross-react with human antigens, thereby contributing to the development of autoimmune disorders.ĭespite their prominent occurrence at the surface of all cells and virus particles, carbohydrates do not elicit immune responses like peptide antigens. The structural similarity between bacterial carbohydrate antigens and surface glycoconjugates of protists, fungi and animals leads to the production of carbohydrate-specific antibodies protective against a broad range of pathogens. We focus on the significance of the intestinal microbiota in shaping carbohydrate-specific antibodies not just in the gut, but also in the blood circulation. Here we explore the development of carbohydrate-specific antibodies in humans, addressing the definition of natural antibodies and the production of carbohydrate-specific antibodies upon antigen stimulation. On the other hand, various carbohydrate-specific antibodies, including antibodies to ABO blood group antigens, emerge after the contact of immune cells with the intestinal microbiota, which expresses a vast diversity of carbohydrate antigens. Carbohydrate-specific antibodies are often classified as natural antibodies under the assumption that they arise without prior exposure to exogenous antigens. Despite their broad occurrence, little is known about their formation and biological significance. Carbohydrate-specific antibodies are widespread among all classes of immunoglobulins.
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