The pathogenesis of HLA-B27 associated arthritis: lessons from the B27 crystal

The most remarkable association between a major histocompatibility complex antigen and disease susceptibility--HLA-B27 and seronegative spondyloarthropathies, particularly ankylosing spondylitis--was discovered 20 years ago. During the two intervening decades advances in basic immunology and molecular biology have not only revealed the biosynthesis and structure of HLA-B27 but also given clues to the basic function of this molecule, the presentation of allele-specific peptides to CD8+ cytotoxic T cells. The recently reported three-dimensional structure of HLA-B27 and the identification of self-peptides bound to this major histocompatibility complex class I antigen can be viewed as a landmark in the understanding of the pathogenic role of HLA-B27. Based on crystallographic evidence, a peptide-binding motif can be postulated that should allow identification of HLA-B27 complexed peptides which may trigger an immune reaction causing arthritis.