Limitations
Controlled exposure studies are usually limited to a single exposure and give information of a certain exposure level and time point, contrary to animal and cell experiments, which allows for larger numbers of scenarios to be investigated. In this study we failed to reach sex balance. Although both male and female subjects were included in the study, we were unable to perform any gender analysis in response to wood smoke, due to the low number of included female subjects. Further studies are warranted to assess if there are gender differences in response to wood smoke, especially when women are predominantly exposed in low- and middle-income countries. An earlier time point for bronchoscopy was chosen in the present study to investigate early airway responses to wood smoke. While aiming for a similar exposure dose (time x exposure concentration) as in the previous study at 24 h post exposure, a shorter exposure time and hence a higher concentration was required to manage logistics for the research subjects, medical staff and laboratory labour. As earlier alluded the PM concentrations in the in vitro experiments were considerably higher than encountered locally in the human lung in vivo