Supplementary Material for: The Human Glycoprotein Salivary Agglutinin Inhibits the Interaction of DC-SIGN and Langerin with Oral Micro-Organisms

Salivary agglutinin (SAG), also known as gp340 or SALSA, is a glycoprotein encoded by the Deleted in Malignant Brain Tumours 1 gene and is abundantly present in human saliva. SAG aggregates bacteria and viruses, thereby promoting their clearance from the oral cavity. The mucosa lining the oral cavity contains dendritic cells (DC) and Langerhans cells (LC), which express the C-type lectin receptors (CLR) DC-SIGN and Langerin, respectively. Both DC-SIGN and Langerin recognise mannose and fucose carbohydrate structures on pathogens and self-glycoproteins to regulate immunity and homeostasis. The purpose of this study was to investigate whether SAG interacts with these CLR and whether this interferes with the binding to oral pathogens. We show that whole parotid saliva and SAG, when coated to microplates, strongly interact with DC-SIGN and Langerin, probably via mannose and fucose structures. Also, primary human DC and LC bind parotid saliva and SAG via DC-SIGN and Langerin, respectively. Furthermore, SAG binding to DC-SIGN or Langerin prevented binding to the micro-organisms Candida albicans and Escherichia coli which express mannose and fucose-containing glycan structures. Thus, binding of saliva glycoprotein SAG to DC-SIGN and Langerin may inhibit pathogen-DC/LC interactions, and could prove to be a new immunomodulatory mechanism of SAG.

唾液凝集素（SAG），亦称为gp340或SALSA，是由Malignant Brain Tumours 1基因编码的糖蛋白，在人类唾液中含量丰富。SAG能聚集细菌和病毒，从而促进其从口腔中被清除。口腔黏膜内含有树突状细胞（DC）和朗格汉斯细胞（LC），分别表达C型凝集素受体（CLR）DC-SIGN和Langerin。DC-SIGN和Langerin均能识别病原体和自身糖蛋白上的甘露糖和岩藻糖碳水化合物结构，以调节免疫和稳态。本研究旨在探究SAG是否与这些CLR相互作用，以及这种相互作用是否会影响其与口腔病原体的结合。研究发现，全腮腺唾液和SAG涂覆于微板时，与DC-SIGN和Langerin存在强烈相互作用，可能通过甘露糖和岩藻糖结构实现。此外，人源初级DC和LC分别通过DC-SIGN和Langerin与腮腺唾液和SAG结合。进一步地，SAG与DC-SIGN或Langerin的结合阻断了表达含有甘露糖和岩藻糖结构的甘聚糖结构的微生物如白色念珠菌和大肠杆菌的结合。因此，唾液糖蛋白SAG与DC-SIGN和Langerin的结合可能抑制病原体与DC/LC的相互作用，并可能证明是SAG的一种新的免疫调节机制。