Immunological and bacteriological studies in smokers with chronic bronchitis and recurrent exacerbations

Abstract

Bronchial infections are common in smokers with chronic bronchitis (CB). Why only some smokers with CB develop problems with recurrent infectious exacerbations is not known. The aim of the present study was to investigate whether changes in systemic and lung immunity and in the intrabronchial microbial flora can explain the propensity to recurrent exacerbations seen in some smokers with CB.Bronchoscopy with bronchoalveolar lavage (BAL), venous blood sampling and a skin prick test were performed in smokers with CB and recurrent exacerbations, asymptomatic smokers and healthy never-smokers. Presence and distribution of lymphocyte subpopulations in blood and BAL were analysed with flow cytometry. Peripheral blood mononuclear cellsí (PBMCs) production of cytokines and prolipherative responses to different stimulators in cell culture were measured. Blood natural killer (NK-) cell activity was analysed. The cutaneous delayed-type hypersensitivity (DTH) reaction to recall antigens was evaluated. Serum content of immunoglobulin (Ig) classes and IgG subclasses was analysed with radial immunodiffusion. A novel two-step BAL procedure for obtaining representative microbial samples from the lower airways was adopted and evaluated.No differences in lymphocyte subpopulations in blood and BAL or in NK-cell activity, and only minor differences in prolipherative responses and cytokine production were found in smokers with CB and recurrent exacerbations compared with asymptomatic smokers. DTH reactivity was higher in men than in women but there was no difference between the study groups. Serum content of IgG and IgG2 was lower in smokers than in never-smokers and this difference was particularly great in women. However, there was no difference between the two smoking groups and no correlation between propensity to recurrent exacerbations and serum IgG2 levels. Lower airway bacterial colonization with normal oropharyngeal flora was seen in asymptomatic smokers as well as in smokers with CB and recurrent exacerbations. The two-step BAL procedure was useful in obtaining uncontaminated microbial samples from the lower airways.No major immunological changes that could explain the propensity to recurrent bronchial infections were seen in smokers with CB and recurrent exacerbations compared with asymptomatic smokers. Immunological differences in the study population could be attributed to smoking and sex but not specifically to CB or tendency for recurrent exacerbations. The influence of smoking and sex on serum levels of IgG2 should be taken into account when normal control ranges are defined. Intrabronchial presence of bacteria is associated to smoking even in the absence of CB.