Ubiquitinated protein detection is often troublesome since in most cases this modification reduces the half-life of targeted proteins, inducing their degradation. Furthermore, ubiquitination is reversible thanks to the action of highly specific deubiquitinases present in all eukaryotic cells. MHC molecules ubiquitination has been demonstrated to be a key event in the regulation of the potent immunostimulatory properties of activated human dendritic cells.