Rat CD27 (TNFRSF7) is a member of the tumor necrosis factor receptor superfamily (TNFRSF). It is a type I transmembrane glycoprotein primarily expressed on the surface of T lymphocytes, B cells, and natural killer (NK) cells. As an important T cell co-stimulatory molecule, CD27 binds to its ligand, CD70. This interaction recruits TRAF2/5, activating the NF-κB and JNK signaling pathways, which promotes T cell proliferation, differentiation, and survival while inhibiting apoptosis. The expression level of CD27 serves as a crucial marker for T cell activation and memory status, and soluble CD27 (sCD27) can act as a clinical marker of immune activation. In cancer immunotherapy, CD27 is a significant target. Agonistic antibodies, such as Varlilumab, can enhance anti-tumor T cell responses and have entered clinical trials.