eLife assessment
This study describes a method to track MHC class II binding peptides on dendritic cell (DC) surfaces using a tetracystein tag and a thiol-reactive dye, which can then be investigated in vitro and in vivo. This is a valuable study for the impact on immunology and potentially other areas where the detection of cell-associated peptides is required. The methods are convincing based on the use of MHC class I/II deficient mice that have significantly reduced signal, but the non-zero background is detected, and it is not clear that this is lower than if the peptides were directly labelled with fluorophores.