Alveolar macrophage activation and polarization signatures in stable lung transplant recipients and chronic lung allograft dysfunction

BACKGROUND: Long-term survival after lung transplantation (LTx) remains highly variable, with chronic lung allograft dysfunction (CLAD) as a major limiting factor. CLAD manifests as bronchiolitis obliterans syndrome (BOS) or restrictive allograft syndrome (RAS) in more than 50% of LTx recipients. In contrast, a subgroup of "super survivors" maintains long-term graft stability for years without immunological complications. These patients show an increased prevalence of alveolar macrophages (AMs), but the mechanisms underlying stable graft function remain unclear. METHODS: Transcriptome profiles of AMs were analyzed in lung tissues of super survivors (n = 15), recipients with BOS or RAS (n = 24), and healthy controls (n = 9) using spatial transcriptomics. AM origin was assessed in sex-mismatched cases (n = 8) using X/Y fluorescence in situ hybridization. RESULTS: In super survivor AMs, upregulated genes were associated with stress control and detoxification (GSTA2, HBA2), innate immune regulation (INAVA), lipid homeostasis (APOE, CES1), and alveolar structure maintenance. Most AMs were donor-derived (61.3%). The majority (78.26%) displayed a pre-activated state with enhanced immune plasticity, while a smaller fraction (13.04%) showed M2-like repair functions. In BOS and RAS lungs, donor-derived AMs (37.4%) were largely replaced by recipient-derived cells. 35.71% of BOS and 56.52% of RAS AMs exhibited a progressive M1-like polarization. Transitional pre-BOS and pre-RAS stages suggested that early post-transplant conditions shape macrophage polarization and influence long-term outcomes. CONCLUSIONS: Stable long-term graft function after LTx is associated with persistence of metabolically adapted donor-derived AMs, whereas CLAD reflects their replacement by inflammatory recipient cells. Preserving protective macrophage populations may help promote a long-term stable immune microenvironment after LTx.