Serum IgG and IgA antibodies to Chlamydia pneumoniae and severity of emphysema

OBJECTIVE: Chronic Chlamydia pneumoniae infection has been identified serologically in patients with COPD. The aim of this study was to examine whether the severity of emphysema is related to elevated antibody titres against C. pneumoniae. METHODOLOGY: We measured antibody titres against C. pneumoniae using ELISA, and assessed the severity of emphysema by the percentage of low attenuation area (%LAA) using high resolution (HR) CT in patients with COPD and in non-smoking control subjects. RESULTS: The mean %LAA was 2.2% in non-smoking controls (n = 28) and 13.3% in COPD patients (n = 94). COPD patients with a high IgG antibody index to C. pneumoniae (> or =2.0, n = 42) had a significantly higher %LAA (16.8%) than those with a low IgG index (<2.0, n = 52) (10.6%, P = 0.01). In addition, COPD patients with a high IgA antibody index (> or =2.0, n = 46) had a significantly higher %LAA (15.9%) than those with a low IgA index (<2.0, n = 48) (10.9%, P = 0.048). COPD patients with a high IgA antibody index also had a significantly lower %DLco than that associated with a low IgA index (68.1% and 80.3%, respectively, P = 0.007). There were no significant differences in age, smoking index or FEV(1)/FVC between these groups. CONCLUSION: These results suggest that high antibody titres against C. pneumoniae are linked with the severity of emphysema on high resolution CT and decreased diffusing capacity to carbon monoxide.