Arterial endothelial expression of α2,8-linked Neu5Gc as a potential target for anti-xeno-antigen inflammation in Cmah-KO mice.

N-glycolylneuraminic acid (Neu5Gc), one of the two major sialic acid species in mammals, cannot be biosynthesized in humans because of the inactivation of the responsible enzyme, CMP-Neu5Ac hydroxylase (CMAH). Consequently, Neu5Gc is recognized as an immunologically foreign molecule, resulting in anti-Neu5Gc antibodies production in humans. Meanwhile, dietary Neu5Gc can be metabolically incorporated into glycans and expressed on tissues. Neu5Gc therefore functions as a xeno-autoantigen in humans. The co-existence of Neu5Gc-containing molecules in tissues and circulating anti-Neu5Gc antibodies is thought to drive human-specific chronic inflammation termed xenosialitis and may contribute to vascular disease such as atherosclerosis. Vascular endothelium is a potential major site of Neu5Gc accumulation. Here, we propose the pathological significance of Neu5Gc accumulation likely depends not only on its presence, but also on the glycan structures on which it is displayed. These endothelial Neu5Gc-containing structures remain poorly defined because of the lack of anti-Neu5Gc antibodies to distinguish linkage- and context-specific epitopes. Here, we characterized a vascular Neu5Gc-containing glycan epitope using novel anti-Neu5Gc monoclonal antibodies. Immunohistochemical analyses of mouse tissues showed enriched localization of the epitope for anti-Neu5Gc monoclonal antibody, #23-5, on arterial endothelium. By correlation analysis of glycosyltransferase gene expression and biochemical analyses, the epitope recognized by #23-5 was identified as an α2,8-linked Neu5Gc-containing disialyl structure. In vivo induction of the #23-5 epitope as a xeno-autoantigen was confirmed using Cmah knockout (Cmah-KO) mice after two days of intravenous administration of per-acetylated ManNGc. These findings provide a structural foundation for future studies of Neu5Gc-dependent vascular xenosialitis.