CD52 is a glycosylphosphatidylinositol (GPI)-anchored glycoprotein expressed on lymphocytes, natural killer cells, eosinophils, neutrophils, monocytes, and dendritic cells 1. On lymphocytes, CD52 is expressed on all lymphocyte populations including mature T and B cells 2. The protein carries N-linked carbohydrate side chains that may function in carbohydrate presentation 3. Functionally, CD52 ligation provides costimulatory signals for T-cell activation and proliferation 1, while soluble CD52 interacts with inhibitory Siglec10 to suppress T-cell function 1. On monocytes, CD52 marks an active phagocytic phenotype with enhanced migration and cytokine production 4. CD52 serves as a dynamic prognostic biomarker in sepsis, with increased expression in lymphocytes correlating with improved outcomes 5. In acute myeloid leukemia, CD52 marks quiescent stem-like cells involved in chemoresistance through CD52-Siglec10 interactions mediating immune evasion 6. CD52 identifies mature polymorphonuclear myeloid-derived suppressor cells in cancer patients 7. Therapeutically, anti-CD52 monoclonal antibody alemtuzumab depletes lymphocytes in leukemia and transplantation, though increased infection risk represents a significant adverse effect 82.