Short-term in vivo exposure to cigarette-smoke increases the fluorescence in rat alveolar macrophages

Alveolar macrophages (AMs) from human smokers exhibit a strong intracellular fluorescence. In order to study the mechanisms behind the fluorescence, we wanted to determine whether it could be induced by short term exposure to smoke. We therefore exposed rats for either one or five days to cigarette smoke. AMs were recovered by bronchoalveolar lavage (BAL), and their fluorescence was quantified by flow cytofluorometry. AMs from rats exposed to two cigarettes, on a single occasion, showed an increased fluorescence compared to controls. The fluorescence was further enhanced by exposing rats to two cigarettes, for five consecutive days. Larger and more granular/complex AMs were more fluorescent than smaller and less granular/complex cells. Smoke-exposed rats (five consecutive days) lavaged immediately after the exposure, had less cells in their BAL fluid than control animals. However, when rats were lavaged three smoke-free days after the exposure, the cell recovery increased, probably due to less airway obstruction. In conclusion, we found that a short-term in vivo exposure to cigarette smoke results in an increased AM fluorescence. The findings can be one explanation for the strong fluorescence seen in AMs from human smokers, possibly due to endocytosis of fluorescent material.