Distribution and phenotype of dendritic cells and resident tissue macrophages in the dura mater, leptomeninges, and choroid plexus of the rat brain as demonstrated in wholemount preparations

Dendritic cells (DC) are regarded as the 'sentinels' of the immune system. They play a crucial role in surveillance of peripheral tissues, trapping an tigens encountered there, and migrating via the lymphatics to lymphoid orga ns where they interact with naive T cells thus generating antigen-specific primary immune responses. Until now it has been assumed DC are largely abse nt from the brain, meninges, and the choroid plexus within the ventricles. Such a situation was thought to partly explain the 'immune privileged' natu re of the central nervous system (CNS). The present study of normal rat tis sues using single and double immunohistochemistry reveals for the first tim e that extensive networks of major histocompatability (MHC) class II+/OX62( +) DC are widely distributed in sites which may potentially encounter CNS a ntigens. These sites included the dura mater, leptomeninges, and the choroi d plexus. These putative DC were negative when stained with the anti-reside nt tissue macrophage monoclonal antibody ED2. In addition to the rich netwo rks of DC, dense populations of resident tissue macrophages (ED2(+) and ED1 (+)) were also demonstrated in the dura mater, leptomeninges and to a lesse r extent in the choroid plexus. The presence of rich networks of DC and mac rophages in the vascular and supporting tissues of the brain may play an im portant role in inflammatory and immune-mediated disorders affecting the CN S, including auto-immune demyelinating diseases such as multiple sclerosis. (C) 1099 Wiley-Liss, Inc.