OBJECTIVES A role for Klebsiella pneumoniaein ankylosing spondylitis (AS) has been suggested because faecal carriage of Klebsiella and serum Klebsiella specific antibodies may be increased in this disease. This study has extended the earlier findings by comparing Klebsiella specific serum IgA class antibodies with inflammatory changes in the gut.

RESULTS Increased IgA antibody concentrations toK pneumoniae associated with gut inflammation in patients with axial form of AS. Such association was not seen in patients with peripheral form of AS.

CONCLUSIONS These findings may provide further evidence for the role of K pneumoniae in the pathogenesis of AS. However, at least some of the patients with axial AS without gut inflammation, as well as patients with peripheral AS did not have increased K pneumoniae antibody concentrations, which may be regarded as evidence against the direct role of K pneumoniae in the pathogenesis. The aetiopathogenetic mechanisms in the axial and peripheral form of AS may be different.