CD3e

CD3e is the epsilon subunit of the CD3 complex, the signal-transducing module noncovalently associated with the T cell antigen receptor. Its cytoplasmic tail carries an ITAM motif that, together with the CD3γ, CD3δ, and ζ-chain ITAMs, initiates ZAP-70 recruitment after antigen engagement. CD3e also stabilizes assembly and surface transport of the TCR-CD3 complex, and murine studies show that anti-CD3e antibodies can modulate T cell responses. The epsilon chain is the target of muromonab (OKT3), the first monoclonal antibody approved for clinical use, and of newer bispecific and tolerogenic anti-CD3 formats. Flow cytometric CD3 antibodies recognize epitopes on CD3e, making it the standard pan-T cell marker.