Real time in vivo investigation of the innate immune response during ventilator-assisted nanoparticle inhalation

Abstract

To visualize and measure in real-time the cellular pulmonary innate immune response elicited by different inhaled nanoparticles (NPs), we apply state of the art intravital microscopy on the alveolar region of the murine lung, in combination with ventilator-assisted inhalation of nebulized NP aerosols.

Quantum-Dot NPs (with carboxyl-, amine-PEG- or PEG-surface modifications) became visible within seconds after the onset of inhalation of nebulized QDs (2.8 µm droplets size) and accumulated as distinct fluorescent spots at the alveolar walls.

As early as 60 min after inhalation, a deposited dose of 16 cm²/g (geom. NP surface /mass lung) elicited an increase in neutrophil numbers as compared to the control group for cQDs, but neither for aQDs nor PEG-QDs. Neutrophils preferentially arrested in microvessels in close proximity to deposited cQD, where they exhibited probing and crawling behavior. This early immune response was not specific to cQDs as a comparable increase in neutrophil numbers was also observed upon inhalation of a bioequivalent dose of carbon black NPs (CNP), a typical component of urban air pollution.

At the same time resident alveolar macrophages (AMs) increasingly internalized cQDs, but only little uptake was detected for aQDs.

Intriguingly, cQDs as well as CNPs increased the migration velocity of AMs in the alveoli of the respective mice, whereas aQDs decreased AM crawling velocity.

Overall, our data indicate a close relation between AM activity (phagocytosis, migration) and the rapid and site-specific recruitment of neutrophils during the early phase of particle inhalation, suggesting a specific role of AMs in triggering the immune response by different NPs.