Galectins Differentially Regulate the Surface Glycosylation of Human Monocytes.

Monocytes are circulating blood cells that rapidly mobilize to inflamed sites where they serve diverse effector functions shaped in part by microenvironmental cues. The establishment of specific glycosylation patterns on the immune cell glycocalyx is fundamental to direct the inflammatory response, but relatively little is known about the mechanisms whereby the microenvironment controls this process. Here, we report that galectins differentially participate in remodeling the surface glycosylation of human primary CD14(+)CD16(-) monocytes under proinflammatory conditions. Using a lectin array on biotinylated protein, we found that the prototypic galectin-1 negatively influenced the expression of galactose epitopes on the surface of monocytic cells. On the other hand, the tandem-repeat galectin-8 and, to a certain extent, the chimeric galectin-3 promoted the expression of these residues. Jacalin flow cytometry and pull-down experiments further demonstrated that galectin-8 causes a profound upregulation of mucin-type O-glycosylation in cell surface proteins from primary monocytes and THP-1 cells. Overall, these results highlight the emerging role of the galectin signature on inflamed tissues and provide new insights into the contribution of extracellular galectins to the composition of the glycocalyx in human monocytes.