IgG subclasses in smokers with chronic bronchitis and recurrent exacerbations

Background-Tobacco smokers have lower serum levels of IgG than nonsmokers. IgG subclass deficiency is common in patients with recurrent respiratory in fections. Recurrent bronchial infections are common in smokers with chronic bronchitis (CB). We have investigated whether susceptibility to recurrent exacerbations in smokers with CB is associated with altered IgG subclass le vels or IgG subclass deficiency. Methods-Serum levels of IgG, IgA, IgM, and IgG subclasses 1-4 were determin ed by radial immunodiffusion in 100 subjects: 33 smokers with stable CB and recurrent exacerbations, 24 asymptomatic smokers, and 43 healthy never smo kers. Systemic tobacco exposure was verified and excluded using a serum cot inine ELISA. Immunoglobulin data were log transformed to enable use of para metric statistical methods. Results-Compared with never smokers, both patients with CB and asymptomatic smokers had significantly lower levels of IgG (median 9.7 gn (range 5.6-15 .2) and 9.9 (6.1-12.1) gn v 12.0 (6.9-18.5) gn) and IgG2 (2.8 (0.9-5.9) gn and 2.5 (1.0-6.3) gn v 4.0 (1.7-10.2) gn). The estimated ratio of median va lues between the patients with CB and never smokers was 0.78 (95% confidenc e interval (CI) 0.69 to 0.89) for IgG and 0.65 (95% CI 0.50 to 0.83) for Ig G2. The corresponding ratios between asymptomatic smokers and never smokers were 0.79 (95% CI 0.69 to 0.91) and 0.60 (95% CI 0.50 to 0.83), respective ly. There were no significant differences between the smoking groups. Conclusions-Susceptibility to recurrent exacerbations in smokers with CB is not associated with lower levels of IgG subclasses than can be accounted f or by smoking per se.