Clone FN50 recognizes the human CD69 antigen, also known as activation inducer molecule (AIM). CD69 is involved in the early events of lymphocyte, monocyte, and platelet activation. Cross-linking of CD69 induces cytotoxic activity and costimulates cytokine production of activated NK cells and selected T cell clones. CD69 is transiently expressed on activated leukocytes including T cells, thymocytes, B cells, NK cells, neutrophils, and eosinophils. It is constitutively expressed by a subset of medullary mature thymocytes, platelets, mantle B cells, and certain CD4+
T cells in germinal centers of normal lymph nodes.