Macrophage Turnover Kinetics in the Lungs of Mice Infected with Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae is the most prevalent cause of community-acquired pneumonia and is known to induce apoptosis and necrosis in macrophages in vivo. We analyzed the kinetics of alveolar and lung parenchymal macrophage replacement by newly recruited exudate macrophages in vehicle-treated and S. pneumoniae-challenged bone marrow chimeric CD45.1 mice. After lethal irradiation, CD45.1 alloantigen-expressing recipient mice were transplanted with bone marrow cells from CD45.2 alloantigen-expressing donor mice. After only 24 hours of low-dose S. pneumoniae infection, approximately 60% of CD45.1(pos) recipient-type alveolar macrophages (AM) were replaced by CD45.2(pos) donor-type exudate AM in bronchoalveolar lavage fluid, and this increased to more than 80% on Day 7 of infection. In contrast, lung parenchymal macrophages of S. pneumoniae-infected chimeric CD45.1 mice were replaced by only about 10% by 24 hours, although this increased to over 80% by Days 3 to 7 of infection. This dramatic macrophage turnover was accompanied by early induction of apoptosis/necrosis in donor-type exudate AM peaking at 6 hours after infection, whereas peak apoptosis/necrosis induction in recipient-type AM was delayed until Day 7. Collectively, these data for the first time demonstrate that S. pneumoniae infection of the lung triggers a brisk turnover of both resident and recruited mononuclear phagocyte subsets, and suggest an important role of exudate but not resident macrophages in re-establishing alveolar and lung homeostasis.

Chemokine Receptor 2-Mediated Accumulation of Fungicidal Exudate Macrophages in Mice That Clear Cryptococcal Lung Infection

“…45 Our gating strategy distinguishes ExMs from AMs, which are both CD11c ϩ AF ϩ on the basis of CD11b expression (present on ExMs and absent on AMs), as recently described. [33][34][35][36] In those studies, ExMs were specifically identified in the lungs of mice with bacterial or viral pneumonia, in which the numbers were much smaller than in the current study. The impressive quantity of ExMs that we identify in this model likely reflects the substantial inflammation induced by cryptococcal lung infection, with recruitment of up to 100 million CD45 ϩ leukocytes per mouse and critical reliance on lung macrophages for clearance of this organism.…”

“…[33][34][35][36] Expression of CD11b, along with varying reports of increased major histocompatibility complex (MHC) class II and costimulatory molecules, distinguishes ExMs from AMs. 33 Exudate macrophages express iNOS indicative of effector function.…”

Local delivery of Granulocyte/Macrophage Colony Stimulating Factor protects mice from lethal pneumococcal pneumonia

“…Briefly, mice were euthanized with an overdose of isoflurane (Baxter, Unterschleissheim, Germany) and bronchoalveolar lavage was performed by repeated intratracheal instillation of 300 μl aliquots of cold PBS supplemented with EDTA (Versen; Biochrom, Berlin, Germany) into the lungs and careful aspiration, until a BAL volume of 1.5 ml was collected as describedrecently (27)(28)(31)(32). Subsequently, BAL was continued until an additional volume of 4.5 ml was collected.…”

“…Collection of BAL for the isolation of resident alveolar macrophages and alveolar recruited leukocytes from mice of the various treatment groups was done as described in detail recently (27)(28)(31)(32). Quantification of BAL fluid neutrophils, eosinophils, and lymphocytes was done on differential cell counts of Pappenheim-stained cytocentrifuge preparations, using overall morphological criteria, including cell size and shape of nuclei and subsequent multiplication of those values by the respective absolute BAL cell counts (27)(28)(31)(32).…”

“…Collection of BAL for the isolation of resident alveolar macrophages and alveolar recruited leukocytes from mice of the various treatment groups was done as described in detail recently (27)(28)(31)(32). Quantification of BAL fluid neutrophils, eosinophils, and lymphocytes was done on differential cell counts of Pappenheim-stained cytocentrifuge preparations, using overall morphological criteria, including cell size and shape of nuclei and subsequent multiplication of those values by the respective absolute BAL cell counts (27)(28)(31)(32). Quantification of resident and recruited mononuclear phagocyte subsets (alveolar macrophages, alveolar dendritic cells, and exudate macrophages) recovered by BAL from the lungs of mice from the various treatment groups was done using FACS-based differences in immunophenotypic profiles as characterized by differences in their cell surface antigen expression profiles of F4/80, CD11b, CD11c, and MHC class II (MHC-II), as outlined below in detail and elsewhere (27).…”