High-mannose intercellular adhesion molecule-1 enhances CD16+ monocyte adhesion to the endothelium

Abstract

Human monocytes have been classified into three distinct groups, classical (anti-inflammatory; CD14+/CD16−), nonclassical (patrolling; CD14+/CD16++), and intermediate (proinflammatory; CD14++/CD16+). Adhesion of nonclassical/intermediate monocytes with the endothelium is important for innate immunity, and also vascular inflammatory disease. However, there is an incomplete understanding of the mechanisms that regulate CD16+ versus CD16− monocyte adhesion to the inflamed endothelium. Here, we tested the hypothesis that a high-mannose (HM) N-glycoform of intercellular adhesion molecule-1 (ICAM-1) on the endothelium mediates the selective recruitment of CD16+ monocytes. Using TNF-α treatment of human umbilical vein endothelial cells (HUVECs), and using proximity ligation assay for detecting proximity of specific N-glycans and ICAM-1, we show that TNF-α induces HM-ICAM-1 formation on the endothelial surface in a time-dependent manner. We next measured CD16− or CD16+ monocyte rolling and adhesion to TNF-α-treated HUVECs in which HM- or hybrid ICAM-1 N-glycoforms were generated using the α-mannosidase class I and II inhibitors, kifunensine and swainsonine, respectively. Expression of HM-ICAM-1 selectively enhanced CD16+ monocyte adhesion under flow with no effect on CD16− monocytes noted. CD16+ monocyte adhesion was abrogated by blocking either HM epitopes or ICAM-1. A critical role for HM-ICAM-1 in mediating CD16+ monocyte rolling and adhesion was confirmed using COS-1 cells engineered to express HM or complex ICAM-1 N-glycoforms. These data suggest that HM-ICAM-1 selectively recruits nonclassical/intermediate CD16+ monocytes to the activated endothelium. NEW & NOTEWORTHY Monocyte subsets have been associated with cardiovascular disease, yet it is unknown how different subsets are recruited to the endothelium. This study demonstrates the formation of distinct ICAM-1 N-glycoforms in the activated endothelium and reveals a key role for high mannose ICAM-1 in mediating proinflammatory CD16+ monocyte adhesion. Presented data identify roles for endothelial N-glycans in recruiting specific monocyte subsets during inflammation.