Organization, sequence and expression of the HLA-B27 gene: a molecular approach to analyze HLA and disease associations.

Among the numerous autoimmune diseases associated with various HLA alleles, the one with the highest relative risk so far reported has been ankylosing spondylitis with HLA-B27. To examine this relationship more directly, we have cloned the gene encoding the HLA-B27 antigen and determined its complete DNA sequence. Comparison of the HLA-B27 sequence with that of the allelic HLA-B27 shows a high level of homology. Mutations are distributed evenly between exons and introns. Exon 1 and intron 1 are the most divergent ones, and the degree of divergence distinctly declines towards the 3' end. The HLA-B57 gene when transfected into murine L cells is expressed on the cell surface and reacts with a panel of monoclonal antibodies directed against monomorphic and polymorphic determinants associated with HLA-B27 antigen. The isolation of this gene allows for the first time a search for structural features which make the HLA-B27 antigen a high risk genetic factor for a group of rheumatoid disorders, in particular ankylosing spondylitis.