Distinct Macrophage Subpopulations Characterize Acute Infection and Chronic Inflammatory Lung Disease

Abstract

Although great progress has been made in delineating lung dendritic cell and lymphocyte subpopulations, similar advances in lung macrophages (MΦs) have been hampered by their intrinsic autofluorescence, cell plasticity, and the complexities of monocyte–MΦ compartmentalization. Using spectral scanning, we define alveolar MΦ autofluorescence characteristics, which has allowed us to develop an alternative flow cytometry method. Using this methodology, we show that mouse lung MΦs form distinct subpopulations during acute inflammation after challenge with LPS or influenza virus, and in chronic inflammatory lung disease consequent to SHIP-1 deletion. These subpopulations are distinguished by differential Mac-1 and CD11c integrin expression rather than classical M1 or M2 markers, and display differential gene signatures ex vivo. Whereas the resolution of acute inflammation is characterized by restoration to a homogenous population of CD11chighMac-1neg/low MΦs reflective of lung homeostasis, chronic inflammatory lung disease associated with SHIP-1 deficiency is accompanied by an additional subpopulation of CD11chighMac-1pos MΦs that tracks with lung disease in susceptible genetic background SHIP-1−/− animals and disease induction in chimeric mice. These findings may help better understand the roles of MΦ subpopulations in lung homeostasis and disease.

Flow Cytometric Analysis of Macrophages and Dendritic Cell Subsets in the Mouse Lung

“…In the past, many groups reported the results of two-parameter approaches to identify myeloid cell subsets in the murine lung. For example, investigators have used CD11b versus CD11c plots to identify alveolar and interstitial macrophages and even DCs (7,23,38). Our data suggest that although this approach allows for a fairly accurate identification of alveolar macrophages, it does not permit discrimination between CD11b 1 DCs, interstitial macrophages, and immature monocytes/macrophages.…”

“…Cells were isolated from enzymatically digested mouse lungs, and after the exclusion of doublets and debris, immune cells were identified by CD45 staining. (A) A sequential gating strategy was first used to identify populations expressing specific markers: alveolar macrophages (MF) (Siglec F antigen/fluorochrome (21)(22)(23). Moreover, the autofluorescence of myeloid cells in the lung may further increase after exposure to environmental particulate matter.…”

Alveolar macrophages in pulmonary host defence – the unrecognized role of apoptosis as a mechanism of intracellular bacterial killing

“…Alveolar macrophages with M2 polarization play a key role in lung development [15]. M2 polarized alveolar macrophages are thought to play important roles in lung homeostasis ensuring tissue remodelling and repair, but emerging data suggest that alveolar macrophages may demonstrate simultaneously both M1 and M2 characteristics during acute inflammation and disease [16]. Differentiated macrophages such as alveolar macrophages have a large surface area with a dynamic cell membrane facilitating active phagocytosis or endocytosis of inhaled particles [17,18].…”

MR imaging and targeting of a specific alveolar macrophage subpopulation in LPS-induced COPD animal model using antibody-conjugated magnetic nanoparticles

“…Alternatively, they may have an immunoregulatory M2 activation, which might be implicated in parasite containment and promotion of tissue remodeling and disease progression. 4,5 Although progress has been made to characterize the surface phenotype, activating signals and molecular pathways associated with different forms of macrophage activation, full delineation of this diversity under in vivo conditions requires further investigation. Therefore, imaging and targeting of a specific AM subpopulation in COPD will be of great importance to understand the molecular events involved in its pathophysiology and/or help in early and better diagnosis.…”