6). At days 3, 5 and 6 no significant differences were observed between the groups (Fig. 6). A similar pattern was observed in the supernatants from the

lung homogenates, with significantly increased G-CSF in the SB group at day 1 (P < 0·0001) but no significant differences at other time-points (Fig. 7). In accordance, in the supernatants of the lung homogenates the concentrations of the PMN chemoattractant MIP-2 were increased significantly at day 1 after challenge in the SB groups compared to the LB group (P < 0·0001, Fig. 8). At days 3, 5 and 6 no significant differences were observed (Fig. 8). Cytokines measured in serum and homogenates from mice challenged Rapamycin with sterile beads were negligible at all time-points compared to mice challenged with P. aeruginosa-containing beads (P < 0·01; Figs 6–8). Lungs are constantly exposed

to inhaled or aspirated pathogens, allergens and irritants. However, the distribution of such elements in the lungs is highly variable. The upper see more airways are colonized with bacteria from the oropharynx, whereas the lower normal airways are sterile. In recent years increasing attention has been drawn to the significance of the different zones in the lungs, in relation to concentration of gases [10,11], to induction and recruitment of inflammation and to severity of tissue damage [12] and presence of bacteria [7]. The present study demonstrates how different sizes of infectious beads can result in different inflammatory responses due to different localization of the infectious beads, as a correlation was observed between infection with small beads, localization of smaller biofilm-like structures in smaller airways and an increased inflammatory response. During the continuous dichotomized division from trachea to the two main bronchi to the respiratory bronchioles, the total trans-sectional area of the airways is increased gradually; however, the trans-sectional area of the individual

airway is reduced gradually. As a consequence, larger particles are captured primarily in the upper airways whereas smaller particles can proceed Elongation factor 2 kinase all the way to the alveoli. From previous studies on deposits of particles in the lungs it would have been optimal with even smaller beads below 10 µm in diameter [13]. However, trying to make smaller beads with a smaller nozzle was not possible due to clotting of the small nozzle. Furthermore, studies on localization of particles in the lungs have been performed on inhalation through nose and/or mouth, whereas our challenge procedure was through a tracheotomia. In addition, our beads were forced through a needle into the left main bronchus with a syringe providing a certain pressure, which may lead to a more peripheral localization of the beads.