Discrimination of rat Brunner's gland carbohydrate antigens by site-specific monoclonal antibodies

• Monoclonal antibodies RGM22, RGM26, and RGM42 react with blood group A antigen.
• RGM42 and RGM22 are specific for α-linked GalNAc and GalNAcα1-3Gal.
• Antigens recognized by RGM22 and RGM42 are abundant in rat Brunner's glands.
• RGM26 is specific for GalNAcα1-3(Fucα1-2)Gal-containing antigens in the rat antrum.
• These mAbs are useful tools for studying mucin structures with peripheral α-GalNAc.

Mucus produced and secreted by gastrointestinal mucosa contains various types of mucins equipped with unique sugar chains considered to play critical roles in protecting mucous membranes; therefore, the identification and verification of mucin sugar chains is important for understanding the underlying mechanisms. In our previous work, we generated three monoclonal antibodies (mAbs), RGM22, RGM26, and RGM42, which recognize sugar chains in rat gastric mucin. Here, we immunohistochemically analyzed the rat gastrointestinal mucosa and found that the antigens recognized by RGM22 and RGM42 were expressed in the rat antrum and Brunner's glands, whereas that recognized by RGM26 was detected in the antrum, but rarely in Brunner's glands. We found that these antibodies reacted with porcine gastric mucin-derived oligosaccharides bearing a common structure: GalNAcα1-3(Fucα1-2)Galβ1-4GlcNAcβ1-6GalNAc-ol. Moreover, epitope analysis revealed that RGM42 and RGM22 recognized α-linked GalNAc and GalNAcα1-3Gal, respectively, on the GalNAcα1-3(Fucα1-2)Gal structure, whereas RGM26 was specific for GalNAcα1-3(Fucα1-2)Gal. These results indicate that rat Brunner's glands express specific antigens bearing GalNAcα1-3Gal that are recognized by RGM22 and RGM42. Thus, RGM22, RGM26, and RGM42 with their unique antigen specificities could be useful tools for investigation of oligosaccharide diversity among mucins.

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