Morphology, localization, and postnatal development of dural macrophages.

The dura mater contains abundant macrophages whose functions remain largely elusive. Recent studies have demonstrated the origin, as well as the gene expression pattern, of dural macrophages (dMΦs). However, their histological features have not been explored yet. In this study, we performed immunohistochemistry and electron microscopy to elucidate their precise morphology, localization, and postnatal development in mice. We found that the morphology, as well as the localization, of dMΦs changed during postnatal development. In neonatal mice, dMΦ exhibited an amoeboid morphology. During postnatal development, their cell bodies elongated longitudinally and became aligned along dural blood vessels. In adulthood, nearly half of the dMΦs aligned along blood vessel networks. However, most of these cells were not directly attached to vessels; pericytes and fibroblasts interposed between dMΦs and vessels. This morphological information may provide further indications for the functional significance of dMΦs.