The starting concentration was set according to the stock concentration of the M86 antibody in the hybridoma supernatant

The starting concentration was set according to the stock concentration of the M86 antibody in the hybridoma supernatant. positive cannot be stained with 27H8 questioning whether commensal bacteria express the native -Gal epitope at all. Keywords:alpha-Gal, -Gal, IgG, monoclonal antibody, carbohydrate, red meat allergy, xenotransplantation, bacteria == 1. Introduction == Carbohydrates are vital and highly diverse structures that are variable between species. Of note, the alpha-Gal (-Gal) epitope is a carbohydrate immunogen in humans that has relevance in allergy and xenotransplantation. The determining structure of the epitope is the disaccharide galactose-1,3-galactose (Gal-1,3-Gal), which naturally occurs as the trisaccharide galactose-1,3-galactose-1,4-N-acetylglucosamine (Gal-1,3-Gal-1,4-GlcNAc) on glycosylated proteins GSK3368715 dihydrochloride or lipids (1). The immunogenic property of the -Gal epitope in humans is HTRA3 based on the loss of the enzyme -1,3-galactosyltransferase (GGTA1) in Catarrhines, including apes and humans, which catalyzes the reaction of Gal-1,4-GlcNAcR + UDP-Gal to Gal-1,3-Gal-1,4-GlcNAc-R + UDP (2). Humans therefore do not express the -Gal epitope in contrast to non-primate mammals. This absence eventually allows for the sensitization of humans and a subsequent development of the so-called -Gal syndrome or red meat allergy that is based on the formation of IgE molecules against -Galviatick bites (35). These IgE molecules may lead to allergic reactions including fatal anaphylaxis following ingestion of mammalian meat or related products such as gelatin or innards, for instance pork kidney, which are major sources of allergen in -Gal-induced meat allergy (69). Moreover, GSK3368715 dihydrochloride sensitization to -Gal can also result in severe allergic reactions in cancer patients who receive Cetuximab, a chimeric human-murine monoclonal antibody that contains -Gal on the Fab fragment (10). Interestingly, antibodies of different isotypes against the -Gal epitope are quite abundant in humans with IgG levels estimated to range between 1% (11) to 0.1% of total plasma IgG with high variability between subjects and lowest abundance in individuals carrying the blood type B antigen (12). The latter observation is likely due to the structural similarity between the -Gal epitope and blood type B antigen, which contains an additional fucose molecule on the second last galactose molecule (1). These human anti–Gal antibodies pose a challenge for xenotransplantation, in particular for pig organ transplantation, which was overcome to some extend with developingGGTA1knockout (KO) pigs (1315). The induction of anti–Gal antibodies has been hypothesized to be mediated by the gut microbiota, since intestinal bacteria are recognized by anti–Gal binding molecules, such as purified polyclonal human anti–Gal antibodies (16,17) or Isolectin B4 fromBandeiraea simplicifolia(BSI-B4) (1820). Furthermore, antibiotics have shown to reduce preexisting anti–Gal antibodies of the IgG isotype (21) and the oral introduction ofEscherichia coliO86:B7 inGgta1KO mice has been shown to induce anti–Gal antibodies (IgG, IgM) (22). BSI-B4and another -Gal-binding lectin from the mushroomMarasmius oreades(MOA) (23) have reduced specificity to the -Gal epitope, as GSK3368715 dihydrochloride they both also bind to the blood group B antigen. The currently most widely used -Gal-specific monoclonal antibody is M86, an IgM antibody which was developed by Galiliet al.inGgta1KO mice (24) and to some degree also chicken single-chain antibody variable-region fragments (scFv) against -Gal developed by Cunninghamet al.(25). Neither of the two antibodies has been convincingly shown to stain bacteria to the authors knowledge. However, the monoclonal antibody M86 was indeed used to show -Gal expression on parasites such asPlasmodiumspecies (18). As the M86 antibody is of the IgM isotype with limited affinity and purification properties, we aimed to establish a novel IgG antibody with high affinity for both the di- and trisaccharide -Gal epitope and with wide applicability. Here, we report the development of a novel IgG1 antibody called 27H8 that is highly specific for both synthetic and naturally occurring GSK3368715 dihydrochloride -Gal epitopes. The 27H8 monoclonal antibody displays high.