Wood smoke exposure induces lymphocyte activation in blood and bronchoalveolar lavage in humans.

<bold>Background:</bold> Exposure to wood smoke has been shown to contribute to adverse respiratory health effects. It is suggested that exposure to fine wood smoke particles induces airway inflammation, but the underlying mechanisms are yet unclear. The aim of the study was to investigate airway and systemic inflammatory responses at an early stage post-exposure. <bold>Methods:</bold> In a double-blinded, randomised crossover study, 14 healthy non-smoking participants were exposed for 2 hours to filtered air and diluted wood smoke with a mean particulate matter concentration of 409 µg/m³ at two different occassions. Six hours after each exposure, blood sampling was performed along with bronchoscopy with bronchial wash (BW) and bronchoalveolar lavage (BAL). Differential cell counts were performed on cells from blood, BW and BAL. Lymphocyte subsets were also analysed with flow cytometry (CD3, CD4, CD8, CD25 and CD69). <bold>Results:</bold> In blood the total lymphocyte numbers were increased at 6 hours post wood smoke exposure, as were CD3+, CD4+ and CD8+ cells. On CD4+ and CD8+ cells, the expression of the CD69 and CD25 activation markers was increased after wood smoke exposure. In BAL and BW, CD4+ and CD8+ lymphocytes expressing CD25 were increased following wood smoke exposure, but total lymphocyte count remained unchanged. <bold>Conclusions:</bold> Acute exposure to wood smoke from incomplete combustion induced an increase in total blood lymphocyte counts and activated lymphocyte subsets 6 hours post-exposure. A similar response with lymphocyte activation was also found in the airways. The activation of lymphocytes may enlighten the mechanisms behind the inflammatory action of wood smoke.