Background
The molecular basis for the strong association of HLA-B27 with ankylosing spondylitis (AS) has not been elucidated. A number of B27 alleles including B*2704 and B*2705 are associated with increased susceptibility to AS; in contrast, the alleles B*2706 and B*2709 are not associated with AS. These alleles differ in amino acid regions that have been shown to influence the interaction with tapasin, an accessory molecule that plays a critical role in incorporating HLA class I into the peptide loading complex (PLC). Our aim was to determine whether B27 subtypes differ in their association with the PLC.