The bacteria klebsiella pneumoniae has been implicated as a possible trigger in ankylosing spondylitis (AS) by several investigators but refuted by others. Researchers MA Stone and colleagues in Canada compared the immune responses of people with AS to their family members without AS and to normal healthy people outside of the family in order to find out whether people with AS exhibit a predominant immune response to K. pneumoniae.

Participants
Twenty-five families with two or more AS patients and 34 normal healthy controls matched with the affected family members for age, sex and ethnicity were enrolled in the study. Everyone had a detailed clinical evaluation and blood drawn to determine immune responses to K. pneumoniae, Salmonella typhimurium, Yersinia enterocolitica and Chlamydia trachomatis.

Results
There was no difference in antibody responses between people with and without AS in the same family for each of the above organisms. However, a higher percentage of people with AS (25.9%) exhibited a predominant response to S. typhimurium compared with unaffected family members (5.9%). Regarding K. pneumoniae, there was no difference between people with and without AS in the same family and normal healthy controls. There was no relationship between immune responses and clinical characteristics.

Conclusion
Their results for affected and unaffected family members demonstrated no significant differences with respect to immune responses to K. pneumoniae and the other bacteria in this study. In addition, K. pneumoniae did not exhibit a predominant immune response in people with AS. The researchers conclude the following: "We find no supportive evidence to implicate a causal role for K. pneumoniae in familial AS."

Resources
Stone MA, Payne U, Schentag C, Rahman P, Pacheco-Tena C, Inman R.D., Comparative immune responses to candidate arthritogenic bacteria do not confirm a dominant role for Klebsiella pneumonia in the pathogenesis of familial ankylosing spondylitis, Rheumatology 2004; 43:148-155.