This editorial summarizes recent discoveries that have revolutionized the understanding of ankylosing spondylitis (AS) pathogenesis and the role of HLA-B27. Genetic studies have identified additional genes influencing AS beyond HLA-B27, including ERAP1 and genes in the IL-23 pathway. ERAP1 provides a molecular basis for its epistatic interaction with HLA-B27 in AS. While supporting a role for peptides, the association of ERAP1 does not necessarily implicate specific epitopes. Reviews discuss evidence that inflammatory pathways like IL-23/IL-17 and membrane-bound TNF drive both inflammation and new bone formation in AS. HLA-B27 may activate these pathways through misfolding and