ERMAP (erythroblast membrane-associated protein) is a transmembrane protein with dual roles in erythroid development and immune regulation. The protein contains an extracellular immunoglobulin fold, a transmembrane segment, and a cytoplasmic B30.2 domain with kinase consensus sequences 1. ERMAP is primarily expressed on erythroid cells during differentiation, with expression levels increasing during erythropoiesis in umbilical cord blood cells and K562 cell lines 23. Beyond erythropoiesis, ERMAP functions as a novel inhibitory immune checkpoint molecule sharing structural homology with B7 family members 4. It negatively regulates T cell activation and macrophage responses, with ERMAP-deficient mice showing enhanced T cell activation, increased pro-inflammatory M1 macrophages, and more severe autoimmune symptoms in experimental models 56. Therapeutically, recombinant ERMAP proteins ameliorate autoimmune diseases like experimental autoimmune encephalomyelitis and type 1 diabetes 4. Paradoxically, ERMAP also serves as an 'eat me' signal for Kupffer cells, forming a complex with galectin-9 and dectin-2 to promote cancer cell phagocytosis, with low tumor ERMAP expression correlating with increased liver metastases 7. This dual functionality positions ERMAP as both an immune checkpoint inhibitor and a tumor suppressor mechanism.