Hypoxia-inducible factor-1α regulation of myeloid cells.

Hematopoietic myeloblasts give rise to macrophages, dendritic cells, and neutrophils. Circulating myeloid cells detect invading microbes using pattern recognition receptors and subsequently orchestrate an innate immune response to contain and kill the pathogens. This innate immune response establishes an inflammatory niche characterized by hypoxia due to host and pathogen factors. Hypoxia-inducible factor (HIF) transcription factors are the primary regulators of the myeloid response to hypoxia. In particular, HIF-1α is a critical hub that integrates hypoxic and immunogenic signals during infection or inflammation. Hypoxia induces HIF-1α stabilization, which drives metabolic and phenotypic reprogramming of myeloid cells to maximize antimicrobial potential. HIF-1α activity in myeloid-derived cells enhances the host response to infection, but may also play a role in pathogenic inflammatory processes, such as atherosclerosis. In this review, we summarize recent advances that have elucidated the mechanism by which myeloid cells regulate HIF-1α activity and, in turn, how HIF-1α shapes myeloid cell function.

Quantification of regional aerosol deposition patterns as a function of aerodynamic particle size in rhesus macaques using PET/CT imaging.

Aerosol aerodynamic particle size is known to affect deposition patterns of inhaled aerosol particles, as well as the virulence of inhaled bioaerosol particles. While a significant amount of work has been performed to describe the deposition of aerosol particles in the human respiratory tract, only a limited amount of work has been performed to describe the deposition of aerosol particles in the respiratory tract of nonhuman primates, an animal model commonly utilized in pharmacological and toxicological studies, especially in the biodefense field. In this study, anesthetized rhesus macaques inhaled radiolabeled aerosols with MMADs of 1.7, 3.6, 7.4 and 11.8 µm to characterize regional deposition patterns. The results demonstrate that the regional deposition pattern shifts as particle size increases, with greater deposition in more proximal regions of the respiratory tract and decreased deposition in the pulmonary region. The results of this study extend the findings of previous studies which demonstrated a similar shift in the deposition pattern as a function of particle size by providing greater resolution of deposition patterns. These data on regional deposition patterns provide a starting point to begin to explore potential mechanisms responsible for the differences in virulence of infectious bioaerosols as a function of particle size and deposition pattern reported in previous studies. Additionally, the data are useful to assess the performance of various deposition models that have been published in the literature.