The UCHT1 monoclonal antibody specifically reacts with the ε chain of the CD3/T lymphocyte antigen receptor complex. The CD3 complex contains γ, δ, and ε chains, and it is part of the TCR complex, expressed by all mature T lymphocytes and by the thymocyte lineage. CD3 enhances the antigen recognition by signal transduction.

Unlike HIT3a, another specific antibody of CD3, the UCHT1 antibody can stain both the surface and intracellular CD3ε. The immobilized UCHT1 can cross-link with the TCR complex, enhancing cellular activation and proliferation.