Anti-CD3 Anticorpo [UCHT1] (PerCP-Cyanine 5.5) (A121943)

The gammadelta T cell receptor for antigen (TCR) comprises the clonotypic TCRgammadelta, the CD3 (CD3gammaepsilon and/or CD3deltaepsilon), and the zetazeta dimers. gammadelta T cells do not develop in CD3gamma-deficient mice, whereas human patients lacking CD3gamma have abundant peripheral blood gammadelta T cells expressing high gammadelta TCR levels. In an attempt to identify the molecular basis for these discordant phenotypes, we determined the stoichiometries of mouse and human gammadelta TCRs using blue native polyacrylamide gel electrophoresis and anti-TCR-specific antibodies. The gammadelta TCR isolated in digitonin from primary and cultured human gammadelta T cells includes CD3delta, with a TCRgammadeltaCD3epsilon(2)deltagammazeta(2) stoichiometry. In CD3gamma-deficient patients, this may allow substitution of CD3gamma by the CD3delta chain and thereby support gammadelta T cell development. In contrast, the mouse gammadelta TCR does not incorporate CD3delta and has a TCRgammadeltaCD3epsilon(2)gamma(2)zeta(2) stoichiometry. CD3gamma-deficient mice exhibit a block in gammadelta T cell development. A human, but not a mouse, CD3delta transgene rescues gammadelta T cell development in mice lacking both mouse CD3delta and CD3gamma chains. This suggests important structural and/or functional differences between human and mouse CD3delta chains during gammadelta T cell development. Collectively, our results indicate that the different gammadelta T cell phenotypes between CD3gamma-deficient humans and mice can be explained by differences in their gammadelta TCR composition.

The alpha/beta T cell receptor complex transmits signals from MHC/peptide antigens through a set of constitutively associated signaling molecules, including CD3-epsilon/gamma and CD3-epsilon/delta. We report the crystal structure at 1.9-A resolution of a complex between a human CD3-epsilon/delta ectodomain heterodimer and a single-chain fragment of the UCHT1 antibody. CD3-epsilon/delta and CD3-epsilon/gamma share a conserved interface between the Ig-fold ectodomains, with parallel packing of the two G strands. CD3-delta has a more electronegative surface and a more compact Ig fold than CD3-gamma; thus, the two CD3 heterodimers have distinctly different molecular surfaces. The UCHT1 antibody binds near an acidic region of CD3-epsilon opposite the dimer interface, occluding this region from direct interaction with the TCR. This immunodominant epitope may be a uniquely accessible surface in the TCR/CD3 complex, because there is overlap between the binding site of the UCHT1 and OKT3 antibodies. Determination of the CD3-epsilon/delta structure completes the set of TCR/CD3 globular ectodomains and contributes information about exposed CD3 surfaces.