Anti-CD3 epsilon antibodies enable researchers to detect and measure the CD3 epsilon antigen in biological samples. This target is a reported synonym of the CD3E gene, which encodes CD3 epsilon subunit of T-cell receptor complex. This protein is known to function in adaptive immune responses and the apoptotic pathway, among other biological roles. The human version of CD3 epsilon has a canonical amino acid length of 207 residues and a protein mass of 23.1 kilodaltons. It is reported to be localized in the cell membrane of cells and notably expressed in the tonsil, spleen, lymph node, bone marrow, and appendix.