Immune checkpoint regulator: a new assignment proposed for the classic adhesion molecule P-selectin glycoprotein ligand-1

P-selectin glycoprotein ligand-1 (PSGL-1) is a major selectin ligand expressed by hematopoietic cells and well known for its role in mediating leukocyte trafficking into inflamed tissue. A recent report by Tinoco et al. examines chronic viral infection and melanoma in PSGL-1 deficient mice (Selplg^−/−) and suggests a previously unknown and selectin-independent function for PSGL-1 as an immune checkpoint regulator that promotes T cell exhaustion (1).