Origin, nature, and some functional considerations of intraventricular macrophages, with special reference to the epiplexus cells

Abstract

Intraventricular macrophages encompass the supraependymal, free‐floating, and epiplexus (Kolmer) cells; the supraependymal cells lie in close apposition to the ventricular ependyma, the epiplexus cells are closely associated with the choroid plexus epithelium, and the free‐floating cells are at a variable distance from the epithelial surface. Although the three cell types are regarded as one cellular entity, the epiplexus cells preponderate. On scanning electron microscopy, the epiplexus cells display diverse morphological forms, ranging from round to bipolar to stellate, and bear a variable number of cytoplasmic processes. Transmission electron microscopy shows the presence of large numbers of lysosomes. The phagocytic nature of epiplexus cells is shown by their intense staining for nonspecific esterase and active uptake of tracers, e.g., horseradish peroxidase and rhodamine isothiocynate, administered intravenously or intraperitoneally. The mode of entry of these tracers in the cerebral ventricles is by way of transepithelial transport. In rats, the population of intraventricular macrophages increases steadily after birth until 17 days of age; thereafter, their cell population remains relatively unchanged. The early upsurge is attributed to proliferation of residential cells and/or influx of circulating monocytes/stromal macrophages through the process of “emperipolesis.” The immunophenotypic features of intraventricular macrophages are consistent with other mononuclear phagocytes being immunoreactive for OX‐42, OX‐18, OX‐6, and OX‐1 and ED1 for the detection of CR3 receptors, MHC class I and II antigens, leucocyte common antigen, and macrophage antigen, respectively. The expression of these antigens is noticeably enhanced following the injection of lipopolysaccharide (LPS) into postnatal rats. Remarkably, the intraventricular macrophages are induced to express MHC class II (Ia) antigen after LPS or interferon‐γ injections. Furthermore, the expression of transferrin receptors as detected with OX‐26 is also upregulated after these treatments. Epiplexus cells are also elicited to display a de novo expression of nitric oxide synthase‐like immunoreactivity following intracerebral injection of LPS. They also respond vigorously to a single nonpenetrative blast. Results of our series of studies suggest that, besides their primary function as scavenger cells, the intraventricular macrophages partake in possible immunological responses and iron regulation in the ventricular system or the brain as a whole. Microsc. Res. Tech. 41:43–56, 1998. © 1998 Wiley‐Liss, Inc.

Scanning Electron Microscopy of Plexus Choroideus in Adult Sheep

“…Even if we have recorded the presence of EPC on the PCH surface, and although their outer morphology is the same as that of some cells considered by other authors as macrophages on the PCH surface (Carpenter et al 1970, M a x w ell andMcGadey 1988;Ling and Wong 1993;Ling et al 1998) we have not made a statement about their origin, because our study in the scanning electron microscope was not supplemented by a confirmation in the transmission electron microscope or histochemically. The outer morphology of epiplexal cells in adult sheep and goats (R ajtová 2000), as well as in the foetal material from both species of small ruminants (R ajtová 1997) is the same as their supraependymal cells under the physiological conditions (R ajtová 1988, 1990Rajtová and Kaãmarik 1998).…”

“…Some authors, engaging in the description of supraependymal or epiplexal cells, have considered them as macrophages capable of movement and phagocytosis (Kitamura 1973;Hosoya and Fujita 1973;Chamberlain 1974;Bleier et al 1975;Sturrock,1983Sturrock, , 1988, or as the structures derived from the macrophages circulating in the blood (Carpenter et al 1970;Ling 1983;Boya et al 1986;Maxwell and McGadey 1988;L u et al 1993;Ling and Wong 1993;Ling et al 1998).…”

Cytology of the Normal and Abnormal Choroid Plexi in Selected Domestic Mammals, Wildlife Species, and Man

“…2 The epiplexus cells (which are greatly outnumbered by the epithelial cells) have also been extensively studied by means of transmission and scanning electron microscopy. [16][17][18] This study describes and illustrates the cytologic anatomy of the choroid plexi of some animals and humans, from the cytopathologist's point of view, and defines at least 4 morphologically distinct cell types, and some morphologic features, for which no previous reports appear to be available.…”

Brain Barriers and the Acute-Phase Response

“…Of note, in vitro studies are a complement of the in vivo work since they permit a dissection of what is the real contribution of the CP epithelial cells; in in vivo studies the complete CP is usually studied, including not only the contribution of epithelial cells but also of all other cells present in the CP stroma. Among these are macrophages, dendritic cells (Hanly & Petito, 1998;Ling et al, 1998;McMenamin, 1999) and fibroblasts. Epiplexus cells may also contribute, this time by interacting on the apical surface of the epithelial cells where they are found (Emerich et al, 2005;Ling et al, 1998).…”

“…Among these are macrophages, dendritic cells (Hanly & Petito, 1998;Ling et al, 1998;McMenamin, 1999) and fibroblasts. Epiplexus cells may also contribute, this time by interacting on the apical surface of the epithelial cells where they are found (Emerich et al, 2005;Ling et al, 1998). All of these cells, particularly macrophages, are able to produce immune modulators that can activate receptors in the basolateral membrane of the CP epithelial cells, ultimately contributing to the overall CP and brain response to inflammation.…”