Macrophages and dendritic cells in the rat meninges and choroid plexus: three-dimensional localisation by environmental scanning electron microscopy and confocal microscopy

Abstract

The present investigation provides novel information on the topographical distribution of macrophages and dendritic cells (DCs) in normal meninges and choroid plexus of the rat central nervous system (CNS). Whole-mounts of meninges and choroid plexus of Lewis rats were incubated with various anti-leucocyte monoclonal antibodies and either visualised with gold-conjugated secondary antibody followed by silver enhancement and subsequent examination by environmental scanning electron microscopy or by the use of fluorochromes and confocal microscopy. Large numbers of MHC class II(+) putative DCs were identified on the internal or subarachnoid aspect of dural whole-mounts, on the surface of the cortex (pia/arachnoid) and on the surface of the choroid plexus. Occupation of these sites would allow DCs access to cerebrospinal fluid (CSF) and therefore allow antigens into the subarachnoid space and ventricles. By contrast, macrophages were less evident at sites exposed to CSF and were more frequently located within the connective tissue of the dura/arachnoid and choroid plexus stroma and also in a sub-pial location. The present data suggest that DC may be strategically located within the CNS to sample CSF-borne antigens. Furthermore, the data suggest that CNS tissue samples collected without careful removal of the meninges may inadvertently be contaminated by DCs and meningeal macrophages.

The Antigen-Presenting Activity of Fresh, Adult Parenchymal Microglia and Perivascular Cells from Retina

“…Studies of brain show that DC are not found in immunologically quiescent parenchyma, but are recruited after the onset of inflammation (10). DC are found in all layers of the meninges, including the pia mater and the choroid plexus (63,64) of the CNS, and could be an important source of recruited APC. This localization of DC will lead to contamination of brain preparations with meningeal-derived DC, unless exceptional measures are taken in the dissection of the brain.…”

After Injection into the Striatum, in Vitro-Differentiated Microglia- and Bone Marrow-Derived Dendritic Cells Can Leave the Central Nervous System via the Blood Stream

“…22 Moreover, cells derived from the different shake-offs are known to have a comparable in vitro phenotype, based on the phagocytic ability, morphology, specific immunoreactivity, cytokine secretion, and LPS response. 35 However, there was still the possibility that our shake-offs also contained blood mononuclear cells that had been trapped in the vasculature, or dendritic/myeloid cells initially located in the perivascular or meningeal compartments, 1,2,36 and that the GM-CSF/ IL-4 -recruited micDCs derived from these cellular sources. To clarify this issue, we produced bone marrow chimeras by injecting hematopoietic stem cells of GFPtransgenic Lewis rats into irradiated wild-type Lewis rats.…”

“…1,2 Under pathological conditions like inflammation, 3 degeneration, 4 infection, 5 and ischemia, 6 these cells increase in numbers, mostly by immigration from the peripheral immune system, but also by differentiation of parenchymal microglial cells. 6,7 While there is ample information available about the recruitment of dendritic cells to the CNS and about their possible contribution to the exacerbation [7][8][9] or attenuation 6 of local immune responses, little is known about the exit of DCs from the CNS.…”

How to drain without lymphatics? Dendritic cells migrate from the cerebrospinal fluid to the B-cell follicles of cervical lymph nodes

“…This point is of importance because DCs are absent from normal CNS parenchyma, 7 but they can be detected in CSF and in compartments associated with CSF circulation or production, including meninges and choroid plexuses. [8][9][10] Moreover, under neuroinflammatory conditions, DCs accumulate in the CSF 11,12 as well as in perivascular spaces, 13,14 anatomic compartments draining into the CSF. These findings, along with others, suggest that the CSF may be a major transport route for DCs circulating in the CNS and migrating either from CSF to CNS parenchyma or from CSF to the lymphoid organs.…”