The UCHT1 monoclonal antibody binds to the human epsilon chain of the CD3 antigen/T cell antigen receptor, a 20- to 30-kDa protein complex. This complex contains a CD3γ, a CD3δ, a CD3ζ (CD247), two CD3ε, and a T cell receptor (α/β or γ/δ) heterodimer (Dong, D., et al. 1981. Nature. 573, 546–552). CD3 is found on all mature T cells, NKT cells, and thymocytes. It plays a role in recognizing antigen, activating cytotoxic T cells and T helper cells, and signal transduction (Weiss A, et al. 1991. Semin Immunol. (5):313-24).The antibody was purified by affinity chromatography and conjugated to the fluorophore.