Humoral immune response to Chlamydia pneumoniae in twins 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 greater than or equal to 40) of serum IgA antibodies (P = 0.003), whereas in women, a significant difference between the pairs was found in the proprotion of IgG seropositive (a titre of greater than or equal to 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.