The strong link between ankylosing spondylitis (AS) and HLA-B27 has been well established.1 Any aetiological agent or mechanism implicated in AS must provide an explanation for the link with HLA-B27. An amino acid sequence homology, QTDRED, found in the variable region of B*2705, (residues 72–77) and the KP2 component ofKlebsiella pneumoniae nitrogenase enzyme (residues 188–193) has been reported.2 Furthermore, AS patients were shown to have increased concentrations of antibodies to a homologous sequence of both B*27052 ,3 and the KP2 component of K pneumoniae nitrogenase reductase2 although some workers have been unable to confirm these results.4 Antibody affinity is often lower with peptide sequences compared with binding by the native protein and this could be because of conformational changes between peptide and the native protein molecule, thereby accounting for these differences in reactivity.

In the light of these conflicting findings, this study was undertaken to measure antibodies to the native KP2 component of nitrogenase reductase enzyme of K pneumoniae, to determine if it has …