CD3, also known as TNFRSF8, is a cell membrane protein of the tumor necrosis factor receptor (TNFR) superfamily. CD3 protein is expressed by activated, but not resting, T and B cells. CD3 can regulate proliferation of lymphocytes and may also play an important role in human immunodeficiency virus replication. As a regulator of apoptosis, CD3 protein induces cell death or proliferation, depending on the cell type, and has been shown to limit the proliferative potential of autoreactive CD8 effector T cells and protect the body against autoimmunity. CD3 protein expression is upregulated in various hematological malignancies, including Reed-Sternberg cells in Hodgkin's disease (HD), anaplastic large cell lymphoma (ALCL) and subsets of Non-Hodgkin's lymphomas (NHLs), and CD3 is also linked to leukocytes in patients with chronic inflammatory diseases, including lupus erythematosus, asthma, rheumatoid arthritis and atopic dermatitis (AD).