Glycosylation-dependent interaction between CD69 and S100A8/S100A9 complex is required for regulatory T-cell differentiation

Cluster of differentiation (CD)69 is a leukocyte activation receptor involved in the maintenance of immune homeostasis and is positively selected in activated regulatory T (Treg) cells, implicating its role during Treg-cell differentiation. By RNA interference, we show that CD69 is not sufficient to support the conversion of CD4+ naive T cells into Treg cells, whereas it does that of human peripheral blood mononuclear cells (hPBMCs) (P < 0.01), suggesting that a ligand-receptor interaction is required for CD69 function. Using immunoprecipitation and mass spectrometry, we identified the S100A8/S100A9 complex as the natural ligand of CD69 in hPBMCs. CD69 specifically associates with S100A8/S100A9 complex as confirmed by in vitro binding and competition assay, and the treatment of CD69 with peptide-N-glycosidase significantly abolishes such association. In agreement, the glycomics analysis determines the glycosylation site and the N-glycan composition of CD69, and terminal removal of sialic acid from that N-...