ERAP1 and infection: In the absence of infection, loss of ERAAP leads to an altered display of MHC class I-bound self-peptides.25-27 As a result, immunization of wild-type mice with ERAAP-deficient cells induces a CTL response against these pMHC complexes.28 Interestingly, a substantial proportion of this response consists of T cells directed against the non-classical MHC class Ib molecule Qa-1b presenting a peptide (FL9) derived from broadly expressed proteins, Fam49 A/B (termed “QFL” T cells).