The 145-2C11 monoclonal antibody reacts with mouse CD3e, the 20 kDa ε chain of the TCR complex. Together with the γ and δ subunits of CD3, the ε subunits are involved in the assembly, trafficking, and surface expression of T-cell receptor complex. CD3 is expressed on thymocytes, mature T cells, and natural killer T cells, and the ε chain enhances the antigen recognition.The 145-2C11 antibody binds to the TCR complex and, depending on the conditions, initiates T cells activation, proliferation, and apoptosis. The soluble antibody seems to block lysis of target cells by antigen-specific cytotoxic T lymphocytes.The 145-2C11 antibody does not cross-react with the rat leukocytes, and it is used as a phenotypic marker for mouse T lymphocytes.