Humoral immune response to Chlamydia pneumoniae in twin discordant for smoking.

OBJECTIVES

The aim of this study was to investigate whether there is a relationship between smoking and Chlamydia pneumoniae specific antibody levels in generally healthy subjects, and whether this possible relationship is dose-dependent.

DESIGN

Match pair study.

SUBJECTS

The study population comprised of 111 same-gender twin pairs from the Finnish Twin Cohort who in a previous study reported the highest discordance between smoking assessed as pack-years.

MAIN OUTCOME MEASURES

Smoking and background data were obtained by a questionnaire, and C. pneumoniae specific serum IgG and IgA antibodies were measured by the micro-immunofluorescence (mIF) test.

RESULTS

A significantly higher proportion of men with a history of smoking had elevated levels (a titre of > or=40) of serum IgA antibodies (P=0.003), whereas in women, a significant difference between the pairs was found in the proportion of IgG seropositive (a titre of > or=128) subjects (P=0.03). Conditional logistic regression analysis revealed that the risk for elevated IgA antibodies suggestive of chronic infection was significantly increased in current or former smokers in men (odds ratio 5.0 with 95% confidence intervals of 1.45-17.3). No dose-response effect was found between smoking and IgG or IgA titres, neither even if men and women were analysed separately.

CONCLUSION

Smoking was significantly associated with elevated IgA antibody levels in men, supporting indirectly the hypothesis that smoking is a contributory factor in the establishment of chronic C. pneumoniae infection.