T-cell surface glycoprotein CD3 epsilon chain (CD3E)

Part of this TCR-CD3 complex present on T-lymphocyte cell surface that plays a vital role in adaptive immune reaction. 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.

Upon TCR engagement, these motifs become phosphorylated by Src family protein tyrosine kinases LCK and FYN, resulting in the activation of downstream signaling pathways (PubMed:2470098). In addition of this function of signal transduction in T-cell activation, CD3E has a vital role in proper T-cell development.