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A7424 - Stereologic Localization of Interstitial Macrophage Subpopulations in Human Lung
Author Block: P. Hume, S. Gibbings, A. McCubbrey, E. F. Redente, C. V. Jakubzick, P. M. Henson, W. J. Janssen; National Jewish Health, Denver, CO, United States.
Rationale: Pulmonary tissue-resident macrophages, composed of alveolar macrophages (AMs) and interstitial macrophages (IMs), play key roles in maintaining lung homeostasis, fighting infection and orchestrating tissue repair. However, despite their noted importance, the precise niches that are occupied by macrophages in the human lung have not been precisely determined, beyond the commonly held thought that IMs exist in the alveolar interstitium. In this context, our group has recently published that in the mouse, IMs may be divided into at least 3 subsets characterized by unique surface marker expression profiles and distinct transcriptional states. Recent work from our group suggests similar subpopulations of IMs also exist in human lung tissue. We postulate that these macrophage subpopulations have distinctive roles that are influenced by their specific environmental niches. The primary objective of this project is to determine the precise anatomic locations in which macrophage subpopulations reside in human lungs and in the mouse. Methods: Whole human lungs that were rejected for transplantation were obtained from deceased smoking and nonsmoking donors. The lungs were processed immediately after arrival at our center and always within 24 hours of the time of death. Mouse lungs were isolated from euthanized mice. Human and mouse lungs were sectioned into individual lobes, fixed, sectioned and sampled for stereology. Immunostaining was performed against specific surface markers to identify macrophage subpopulations. Using confocal fluorescent microscopy, uniform random fields of view were analyzed for stereological counting of macrophage subpopulation number density per parenchymal, perivascular or peribronchial tissue compartment. Results: A panel of fluorescent conjugated antibodies for flow cytometry experiments has been successfully adapted for the direct visualization of AMs and IM subpopulations by microscopy. We have shown that murine IMs are more likely to be found in proximity to the airways or vessels, as opposed to in the parenchyma. Our preliminary studies in humans demonstrate similar findings. There are increased numbers of both human AM and IMs in cigarette smokers. Formal numerical quantification by stereology is ongoing. Conclusions: Contrary to the conventional dogma that IMs exist in the so-called interstitial compartment between alveolar epithelium and endothelium, we show that IM populations in mouse lung are localized in greatest density in proximity to the bronchovascular bundles. Preliminary human lung data is in agreement with this murine finding.