CD2 is a surface antigen of the human T lymphocyte lineage that is expressed on all peripheral blood T cells. It is one of the earliest T cell markers，being present on more than 95% of thymocytes; it is also found on some natural killer cells but not on B lymphocytes.CD2 interacts with lymphocyte function associated antigen (LFA3) and CD48/BCM1 to mediate adhesion between T cells and other cell types. CD2 is implicated in the triggering of T cells，the cytoplasmic domain is implicated in the signaling function. It is useful for the identification of lymphomas and leukaemias of T cell origin.