Protection of Cellular Antigens from Xenoreactive Responses as Overcoming Strategies

β-d-Mannoside β1,4N-acetylglucosaminyl-transferase-III (GnT-III) as a catalytically branching enzyme of glycoprotein N-glycans generates a bisecting GlcNAc residue in N-linked oligosaccharides. GnT-III as a bisecting enzyme glycosylates to add a GlcNAc residue to the core Man residue of the complex type N-glycans. The GnT-III enzyme therefore inhibits further enzymatic glycosylation of glycans by competitively acting glycosyltransferases of α1,3-d-mannoside β1,4-N-acetylglucosaminyltransferase-IV (GnT-IV) and α-1,6-d-mannoside β1,6-N-acetylglucosaminyltransferase V (GnT-V), in the Golgi apparatus [1]. The bisected GlcNAc residue itself blocks the additional glycosylation activities of complex type N-glycans by other competitive glycosyltransferases [2]. Non-α1,3Gal antigenicity is mainly found in the terminal residues in the N-linked oligosaccharides of glycoproteins. Therefore, the GnT-III action reduces the antigenic levels of non-α1,3-Gal antigen-bearing N-linked oligosaccharides [3, 4].