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Quantitation of neutrophil migration in acute bacterial pneumonia in rabbits
C M Doerschuk1, J Markos, H O Coxson
1University of British Columbia Pulmonary Research Laboratory, St. Paul's Hospital, Vancouver, Canada.
Abstract:
The circulating neutrophils must slow down, adhere to the vessel walls, and migrate out of the microvasculature into the tissue and air spaces to defend the lung against microorganisms. The present study was designed to provide quantitative information about each of these steps. Streptococcus pneumoniae was instilled into the left lower lobe of New Zealand White rabbits to induce a pneumonia, and this lobe was compared with the same region of the opposite lung. The distribution of blood flow was determined by using radiolabeled macroaggregated albumin, and the patterns of perfusion within the capillary bed were quantitated using Monastral blue. The number of neutrophils delivered to the pneumonic site was determined by multiplying the circulating neutrophil count and blood flow. The results show that retention of 51Cr-labeled neutrophils was increased in the pneumonic region 2, 4, and 8 h after instillation of the organisms. The number of intracapillary neutrophils was increased in the pneumonic regions at all time points and in the control regions at 1 and 4 h. Neutrophil migration occurred in the pneumonic site, but only 1-2% of the total neutrophils delivered to the region migrated out of the pulmonary vessels into the air space. We conclude that the circulating neutrophils undergo a generalized response that increases their margination throughout the lung, that increased margination in the pneumonic site changes the distribution of capillary flow, and that the majority of neutrophils delivered to a pneumonic site are returned to the circulation without migrating into the air space.
Insights
Neutrophils slow and adhere to blood vessels during pneumonia, but most return to circulation without entering lung air spaces. This study quantifies neutrophil margination and migration in pneumonia.
Area of Science:
- Pulmonary Medicine
- Immunology
- Microbiology
Background:
- Neutrophils are critical for lung defense against microbial invasion.
- Effective neutrophil function requires slowing, adhering to vessel walls, and migrating into tissues.
Purpose of the Study:
- To quantitatively assess neutrophil margination and migration during pneumonia.
- To understand neutrophil behavior in response to Streptococcus pneumoniae infection in the lung.
Main Methods:
- Inducing pneumonia in rabbits by instilling Streptococcus pneumoniae.
- Quantifying blood flow distribution using radiolabeled macroaggregated albumin.
- Measuring neutrophil margination and migration using radiolabeled neutrophils and Monastral blue staining.
Main Results:
- Increased retention of neutrophils in the pneumonic lung region at 2, 4, and 8 hours post-infection.
- Elevated numbers of intracapillary neutrophils in pneumonic and control regions.
- Limited neutrophil migration (1-2%) from pulmonary vessels into air spaces at the pneumonic site.
Conclusions:
- Neutrophil margination increases generally throughout the lung during pneumonia.
- Enhanced margination alters pulmonary capillary blood flow distribution.
- Most neutrophils delivered to pneumonic sites are re-circulated rather than migrating into air spaces.