Recent Chlamydia pneumoniae infection is highly associated with active ankylosing spondylitis in a Chinese cohort

The aim of the present study was to investigate the presence of anti-Chlamydia pneumoniae (Cp) antibodies in patients with ankylosing spondylitis (AS) to determine whether there is an association with AS disease activity.

Seventy-nine AS outpatients and 73 normal controls were enrolled in this case-control study. Serum anti-Cp immunoglobulins (CpIg) were detected by enzyme-linked immunosorbent assay (ELISA). Antibodies to Epstein-Barr virus (EBV), cytomegalovirus (CMV), and Chlamydia trachomatis (Ct) were also measured. Clinical and experimental data were collected, and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was determined. Patients with positive Cp IgM or Cp IgA were considered to have had a recent Cp infection.

Cp IgG was detected in the majority of AS patients and also controls (88.8% vs. 91.8%, respectively). The seroprevalence of Cp IgA and Cp IgM was significantly higher in AS patients than in the controls (51.9% vs. 31.5%, p = 0.010 for Cp IgA; 79.7% vs. 20.5%, p < 0.0001 for Cp IgM). Seropositivity of Cp IgM was associated with elevation of the disease activity index, including erythrocyte sedimentation rate (ESR; p = 0.021), C-reactive protein (CRP; p = 0.007) and the BASDAI (p = 0.009). Persistent positive Cp IgM was associated with active disease, while seroreversion of Cp IgM was associated with a reduction in these disease activity indices. There was no correlation between Cp IgM or Cp IgA and symptomatic upper respiratory infections or other clinical manifestations.

Recent Cp infections occur frequently in AS patients and Cp IgM antibody is correlated with active disease. These findings indicate that Cp infections may be a triggering factor for active AS.