The present invention relates to the seminal discovery that P-selectin glycoprotein ligand-1 (PSGL-1) modulates the immune system and immune responses. Specifically, the present invention provides PSGL-1 agonists and antagonists which increase the survival of multifunctional T cells and viral clearance. The present invention further provides methods of treating infectious diseases, cancer and immune and inflammatory diseases and disorders using a PSGL-1 modulator.
