The UCHT1 monoclonal antibody reacts with human CD3e, a 20 kDa subunit of the TCR⁄CD3 complex. Along with the other CD3 subunits γ and δ, the ε chain is required for proper assembly, trafficking and surface expression of the TCR complex. CD3 is expressed by developing thymocytes and by all mature T cells. Crosslinking of TCR via immobilized UCHT1 results in T cell proliferation.