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The cell biology and pathogenic role of pulmonary intravascular macrophages
1Department of Environmental Science and Physiology, Harvard School of Public Health, Boston, Massachusetts 02115.
Abstract:
Pulmonary intravascular macrophages (PIMs) are an extensive population of mature phagocytic cells adherent to the pulmonary capillary endothelium in selected species. They are not prevalent in lungs of commonly studied laboratory animals, such as rodents, and thus have only been recently appreciated. However, their potential role in host defense and acute lung injury has attracted interest, since a number of studies have demonstrated pulmonary localization of circulating particles, microbes, and endotoxin by PIMs. Those animal species, such as ruminants, that provide useful models of pathogen (or endotoxin)-induced acute lung injury demonstrate rapid pulmonary uptake of bacteria by PIMs. Inflammatory mediators released by activated PIMs may initiate the process and provoke accumulation of neutrophils and platelets. This review summarizes the morphological characteristics of PIMs and their species distribution. The role of these members of the mononuclear phagocyte system, both beneficial and potentially pathogenic, is reviewed. The question of whether PIMs have a role in acute lung injury in humans is also discussed.
Insights
Pulmonary intravascular macrophages (PIMs), recently appreciated phagocytic cells, rapidly uptake pathogens in animal models of acute lung injury. Their role in host defense and disease initiation warrants further investigation.
Area of Science:
- Immunology
- Cell Biology
- Pulmonary Medicine
Background:
- Pulmonary intravascular macrophages (PIMs) are mature phagocytic cells found in pulmonary capillaries.
- PIMs are not common in rodents but are significant in species like ruminants, which serve as models for acute lung injury.
- Recent studies highlight PIMs' role in localizing circulating particles, microbes, and endotoxins within the lungs.
Purpose of the Study:
- To review the morphological characteristics and species distribution of PIMs.
- To explore the beneficial and pathogenic roles of PIMs in the mononuclear phagocyte system.
- To discuss the potential involvement of PIMs in human acute lung injury.
Main Methods:
- Literature review of studies on PIMs.
- Analysis of PIMs' role in host defense and acute lung injury models.
- Examination of PIMs' interaction with pathogens and inflammatory mediators.
Main Results:
- PIMs are prevalent in ruminant lungs and rapidly internalize bacteria in acute lung injury models.
- Activated PIMs release inflammatory mediators that may trigger neutrophil and platelet accumulation.
- PIMs' function in host defense and their potential contribution to lung injury are significant.
Conclusions:
- PIMs play a crucial role in the pulmonary response to pathogens and endotoxins, particularly in susceptible species.
- Understanding PIMs' function is key to developing treatments for acute lung injury.
- Further research is needed to determine the role of PIMs in human lung diseases.