CD27 is also known as S152 and T14. A member of the tumor necrosis factor receptor (TNFR) superfamily, it is a 45 kD protein expressed on peripheral T cells, memory B cells, NK cells, and thymocyte subset. Through its ligand, CD70, CD27 plays a key role in T cell and B cell interactions. Additionally, ligation of CD27 on naive T cells may be important in their maturation to effector cells.