Alveolar Macrophages: Development, Respiratory Homeostasis, Signal Pathways, Diseases, and Therapeutic Opportunities

Alveolar macrophages (AMs), as primary immune sentinels in the respiratory tract, are uniquely adapted to tissue-specific demands shaped by local factors and the physiological environment, maintaining airway homeostasis through the clearance of surfactants and particulates. While AMs exhibit remarkable plasticity shaped by dynamic microenvironmental cues, the traditional M1/M2 paradigm fails to adequately capture this complex heterogeneity, and the specific role of AMs in the pathogenesis of pulmonary diseases, as well as AM-centric therapies, remain to be fully elucidated. This review systematically synthesizes the current understanding of AM ontogeny, homeostatic regulation, and their signaling pathways in lung homeostasis and pathologies. Furthermore, we propose a refined conceptual framework categorizing AMs into five distinct functional subtypes to better capture their in vivo plasticity. Then, pathological shifts in the lung microenvironment that drive the pathogenesis of diverse pulmonary disorders, including asthma, chronic obstructive pulmonary disease, acute lung injury, and pulmonary fibrosis, and trigger dysregulated transcriptional and metabolic reprogramming in AMs, are comprehensively discussed. Finally, we explore emerging therapeutic avenues, including metabolic modulation, trained immunity, and autophagy-apoptosis balance restoration. By addressing challenges in precisely regulating AM function, this overview provides a concise yet comprehensive framework for advancing AM-centric therapies in respiratory medicine.