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Nature Immunology 9, 829–830 (1 August 2008) | doi:10.1038/ni0808-829

Cat and mouse

Julio C Delgado & Peter E Jensen

The endoplasmic reticulum aminopeptidase ERAAP (also called ERAP1) participates in the major histocompatibility complex (MHC) class I antigen-processing pathway through its ability to trim peptides delivered into the endoplasmic reticulum lumen by the transporter associated with antigen processing (TAP). ERAAP may be critical in antigen presentation to CD8+ T cells, as many peptides delivered by TAP exceed the eight- to eleven–amino acid length optimal for binding to MHC class I molecules.