T-cell surface glycoprotein CD3 epsilon & CD3 gamma chain, also known as CD3E & CD3G , are single-pass type I membrane proteins.When antigen presenting cells (APCs) activate T-cell receptor (TCR), TCR-mediated signals are transmitted across the cell membrane by the CD3 chains CD3D, CD3E, CD3G and CD3Z. All CD3 chains contain immunoreceptor tyrosine-based activation motifs (ITAMs) in their cytoplasmic domain.