Microglia with distinct origins and non-canonical phenotypes coexist within the border-like niche of the brain's circumventricular organs.

Microglia in brain's circumventricular organs exhibit unique origins and phenotypes, with a distinct CLEC7A high subset and diverse ontogeny, including long-lived monocyte-derived cells.

• Why it matters: Understanding how these specialized immune environments influence macrophage identity is crucial because CVOs lack the blood-brain barrier and are key to sensing blood-borne signals, impacting brain-immune interactions and disease processes.
• What they did: Using multi-omics approaches, the study characterized immune cell populations in the area postrema and median eminence, revealing heterogeneity, ontogenetic diversity, and phenotypic adaptations shaped by aging and metabolism.
• The result: Findings demonstrate that CVO microglia and border-associated macrophages are tailored to their environment, enabling these regions to meet specific immune and metabolic demands, and highlighting their role as specialized immune niches.