XBP1 and ankylosing spondylitis: They demonstrated that PBMCs isolated from Taiwanese with Ankylosing Spondylitis carrying the ERAP1-001 haplotype, leading to ERAP1 overexpression, display higher production of β2m-free heavy chain (FHCs) and FHC dimers, UPR (BiP, CHOP and XBP1), autophagy (Beclin-1, LC3 I and LC3 II) and inflammatory (caspase 1 and IL-1β) markers, compared to ERAP1-002 homozygous donors, who produce lower ERAP1 quantity (Wang et al., 2022).