T-cell surface glycoprotein CD3 delta chain (CD3D)

Part of this TCR-CD3 complex present on T-lymphocyte cell surface that plays an essential role in adaptive immune response. When antigen presenting cells (APCs) activate T-cell receptor (TCR), TCR-mediated signals are transmitted across the cell membrane from the CD3 chains CD3D, CD3E, CD3G and CD3Z.

Upon TCR engagement, these motifs become phosphorylated by Src family protein tyrosine kinases LCK and FYN, leading to the activation of downstream signaling pathways (PubMed:2470098). In addition of this function of signal transduction in T-cell activation, CD3D plays an essential role in thymocyte differentiation.