 It is also implicated in T cell differentiation as well as lymphocyte retention in lymphoid organs.The activation of T lymphocytes and Natural Killer (NK) Cells, both in vivo and in vitro, induces expression of CD69.This molecule, which appears to be the earliest inducible cell surface glycoprotein acquired during lymphoid activation, is involved in lymphocyte proliferation and functions as a signal-transmitting receptor in lymphocytes, including natural killer (NK) cells, and platelets (Cambiaggi et al., 1992) [supplied by OMIM].