ERAP1 and ankylosing spondylitis: In flu-infected B27/ERAP-/- mice, the CD8+ T cell reaction to the B27/NP383–391 epitope is significantly reduced in the absence of ERAP1 As the correlation between ERAP-1 and ankylosing spondylitis (AS) is seen exclusively in HLA-B27+ patients, it appears that creating the B27-related immunodominant peptide of the flu virus depends on ERAP-1, but this is not the case for HLA B-7 (42).