Diversity and immune dynamics of choroid plexus macrophages are shaped by distinct developmental origins

The choroid plexus forms a key barrier and signaling interface between the brain and peripheral circulation, yet its immune landscape remains incompletely understood. Using single-cell transcriptomics combined with lineage and spatial tracing methods, we identified three biologically distinct populations of choroid plexus macrophages, defined by differential expression of CD163, MHCII or CD9. These subsets arise from separate hematopoietic waves, occupy distinct anatomical niches and differentially rely on CSF1 and IL-34 for survival. We found that TGFβ signaling is essential to maintain their tissue-specific identities, and deletion of Tgfbr2 in these cells induces broad phenotypic reprogramming. During neuroinflammation, choroid plexus macrophages mount type I interferon responses and secrete chemokines that recruit CD8+ T cells. Finally, analysis of human choroid plexus reveals macrophage subsets corresponding to those found in mice, indicating evolutionary conservation of their molecular and immune features. Together, these findings define the developmental origin, niche specialization and immune dynamics of choroid plexus macrophages.