Division of Immunology, Tulane National Primate Research Center, Covington, LA 70433;
J Immunol. 2014 Mar 15;192(6):2821-9. doi: 10.4049/jimmunol.1302269. Epub 2014 Feb 17.
Alveolar macrophages (AMs) obtained by bronchoalveolar lavage (BAL) are commonly used to study lung macrophage-mediated immune responses. Questions remain, however, about whether AMs fully represent macrophage function in the lung. This study was performed to determine the contribution of interstitial macrophages (IMs) of lung tissue to pulmonary immunity and that are not present in BAL sampling. In vivo BrdU injection was performed to evaluate the kinetics and monocyte/tissue macrophage turnover in Indian rhesus macaques (Macaca mulatta). Lung macrophage phenotype and cell turnover were analyzed by flow cytometry and immunohistochemistry. AMs and IMs in lungs of rhesus macaques composed ∼70% of immune response cells in the lung. AMs represented a larger proportion of macrophages, ∼75-80%, and exhibited minimal turnover. Conversely, IMs exhibited higher turnover rates that were similar to those of blood monocytes during steady-state homeostasis. IMs also exhibited higher staining for TUNEL, suggesting a continuous transition of blood monocytes replacing IMs undergoing apoptosis. Although AMs appear static in steady-state homeostasis, increased influx of new AMs derived from monocytes/IMs was observed after BAL procedure. Moreover, ex vivo IFN-γ plus LPS treatment significantly increased intracellular expression of TNF-α in IMs, but not in AMs. These findings indicate that the longer-lived AMs obtained from BAL may not represent the entire pulmonary spectrum of macrophage responses, and shorter-lived IMs may function as the critical mucosal macrophage subset in the lung that helps to maintain homeostasis and protect against continuous pathogen exposure from the environment.
肺泡巨噬细胞（AMs）通过支气管肺泡灌洗（BAL）获得，常用于研究肺巨噬细胞介导的免疫反应。然而，关于 AM 是否完全代表肺中的巨噬细胞功能仍存在疑问。本研究旨在确定肺组织间质巨噬细胞（IMs）对肺免疫的贡献，而这些细胞在 BAL 采样中并不存在。体内 BrdU 注射用于评估印度猕猴（Macaca mulatta）中动力学和单核细胞/组织巨噬细胞的更新。通过流式细胞术和免疫组织化学分析肺巨噬细胞表型和细胞更新。在恒稳态下，BAL 猕猴肺中的 AM 和 IM 组成了肺中约 70%的免疫反应细胞。AMs 代表了更大比例的巨噬细胞，约 75-80%，并且表现出最小的更新。相反，IMs 的更新率与血液单核细胞相似，表明血液单核细胞不断取代凋亡的 IMs。尽管 AM 在恒稳态下看起来静止不动，但在 BAL 手术后观察到新的 AM 从单核细胞/IM 中大量涌入。此外，体外 IFN-γ 加 LPS 处理显著增加了 IM 中 TNF-α的细胞内表达，但 AM 中没有。这些发现表明，从 BAL 获得的寿命更长的 AM 可能不能代表整个肺巨噬细胞反应谱，寿命更短的 IM 可能作为肺中关键的黏膜巨噬细胞亚群，有助于维持恒稳态并防止环境中持续的病原体暴露。
