GEOapplication/xmlftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE314nnn/GSE314207/primaryOK200TranscriptomicsMus musculusExpression profiling by high throughput sequencinghttps://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE314207GEOGSEfalseAlveolar Macrophages Undergo a Postnatal Transition from a Hyperphagocytic and Proinflammatory Profile to a Tolerogenic ProfileAlveolar Macrophages (AMs) are crucial for lung immunity and homeostasis. While the ontogeny of AMs is well characterized, their postnatal phenotypic and functional maturation remains unclear. Here, we developed a bronchoalveolar lavage (BAL) protocol across key developmental stages and systematically analyzed age-dependent changes in AMs. AM numbers increased with age, acquiring a mature phenotype alongside alveolar maturation.BAL-recovered AMs decreased in size and increased in roundness from day 3 onward and revealed distinct gene expression profiles across different ages. Functionally, phagocytic capacity peaked in 3-day-old mice. Furthermore, AMs from all ages beyond day 1 showed lower basal inflammatory cytokine expression and an attenuated response to LPS, indicating a postnatal transition toward a tolerant phenotype. The transition from a hyper-phagocytic, pro_x0002_inflammatory neonatal profile to a tolerogenic adult phenotype underscores the intrinsic adaptation of AMs to the immunotolerant microenvironment of the mature lung. Our study provides a comprehensive kinetic profile of postnatal AM development.2026/04/19GSE314207GSM9385009GSM9384997GSM9384998GSM9385008GSM9384999GSM9385010GSM9385001GSM9385012GSM9385011GSM9385000GSM9385014GSM9385003GSM9385013GSM9384992GSM9385002GSM9384993GSM9385005GSM9385004GSM9385015GSM9384994GSM9385007GSM9384995GSM9385006GSM938499634290314207Mus musculus