The CD3 epsilon subunit of the TCR contains endocytosis signals

Ligand binding to TCR induces its internalization and cell surface down-mod ulation. These phenomena contribute to the extinction of activation signals . Due to the multicomponent nature of the TCR-CD3 complex, its internalizat ion may be mediated by one or several of its subunits, Although it has been reported that CD3 gamma and CD3 delta contain endocytosis motifs involved in the internalization of the TCR-CD3 complex, other subunits could also be involved in this process. For instance, CD3 epsilon and CD zeta display am ino acid sequences reminiscent of internalization motifs. To investigate wh ether CD3 epsilon bears endocytosis signals, we have analyzed the internali zation capacity of a panel of deletion and point mutants of CD3 epsilon tha t were expressed on the cell surface independently of other TCR-CD3 subunit s, Here we report that CD3 epsilon displays endocytosis determinants. These data indicate that CD3 epsilon could contribute to the internalization and cell surface down-regulation of TCR-CD3 complexes, Moreover, the existence of endocytosis signals in this polypeptide could serve to retrieve unassem bled CD3 epsilon subunits or partial CD3 complexes from the plasma membrane , thus restricting the expression on the cell surface to fully functional T CR-CD3 complexes.