Molecular mimicry in HLA-B27-related arthritis

A unique feature of patients with ankylosing spondylitis and reactive arthritis is that almost all share the HLA type B27. The primary structures of the HLA-B27 antigens have been determined. At least six variants exist. However, disease predisposition does not appear to be restricted to a particular variant. One hypothesis about the pathogenesis of arthritis is that the bacteria that cause the arthritis carry components that are cross-reactive with HLA-B27 antigens. Several reactive bacterial components have indeed been identified using monoclonal anti-HLA-B27 antibodies. Even more striking is the identification, through a computerized search, of a Klebsiella protein. This protein carries a stretch of six amino acids identical to residues 72 to 77 of two of the HLA-B27 variants. A synthetic peptide carrying these six amino acids of HLA-B27 protein is reactive with serum antibodies in some patients with arthritis. With this knowledge, investigators will be able to formulate new approaches for examining the pathogenesis of HLA-B27-associated arthritis.

A monoclonal anti-HLA-B27 antibody which is reactive with a linear sequence of the HLA-B27 protein is useful for the study of molecular mimicry

In the search for cross-reactivity between bacteria and HLA-B27, three groups of investigators have identified several bacterial envelope proteins which are reactive with the monoclonal anti-HLA-B27 antibodies B27.M1 and B27.M2. Since these two antibodies react poorly with HLA-B27-derived synthetic peptides, it is not possible to locate the reactive epitopes on the HLA-B27 using synthetic peptides. Here, we introduce Ye-2, a monoclonal anti-HLA-B27 antibody which, unlike B27.M1 and B27.M2, is reactive with a synthetic peptide derived from residues 63-84 of HLA-B27.1. Analysis with a cross-reactive peptide derived from residues 226-244 of bovine carbonic anhydrase suggests that only a few of the amino acid residues in the HLA-B27-derived peptide are responsible for the reactivity. This antibody should be a useful adjunct in a preliminary assessment of whether a bacterial protein mimics HLA-B27 in primary structure.