Abstract
Idiopathic pulmonary fibrosis (IPF) is characterised by progressive parenchymal remodelling, driven by epithelial dysfunction, fibroblast activation, and altered immune regulation within the distal lung. Alveolar macrophages (AMs) reside in a surfactant-rich environment and are specialised for continuous lipid handling, yet the significance of this metabolic role for macrophage heterogeneity and fibrotic progression has remained incompletely integrated across studies. In this review, we synthesise evidence from human lung tissue, experimental models, lipidomic analyses, and clinical investigations to place macrophage populations described in IPF-including FABP4-high homeostatic cells and SPP1-associated disease-enriched states-within a unified lipid-metabolic context. We show that macrophage heterogeneity in IPF can be understood as a variation within a core lipid-handling programme rather than the emergence of distinct macrophage lineages. Profibrotic macrophage states are characterised by altered lipid processing and signalling, including dysregulated sterol handling, lysophospholipid pathways, and eicosanoid balance, which impair surfactant turnover and contribute to fibroblast activation. Importantly, experimental and clinical data indicate that macrophage lipid-metabolic programmes remain modifiable, although definitive disease-modifying efficacy in IPF has yet to be established. Framing macrophage states within a lipid-metabolic framework provides a coherent basis for interpreting heterogeneous datasets and supports the rationale for therapeutic strategies aimed at stabilising or restoring macrophage lipid handling in fibrotic lung disease.