Regional difference of lipid distribution in brain of apolipoprotein E deficient mice.

According to recent knowledge, apolipoprotein E (apo E) plays a significant role in the homeostasis of intracellular cholesterol level in various tissues. Apo E deficient mice develop hyperlipidemia, and suffer from atherosclerosis in extracerebral blood vessels and neurodegeneration in the central nervous system. Furthermore, Walker et al. (Am. J. Path., 1997;151:1371-1377) demonstrated cerebral xanthomas of various sizes in the brain of apo E deficient mice. In the present study, it is illustrated that in the homozygous apo E deficient mice of advancing age, a great number of foamy macrophages extravasate from microvessels in thalamus and fimbria hippocampi, and scatter in the perivascular regions and migrate toward the ependyma, fimbria hippocampi, hippocampus, and thalamus. Here, it must be pointed out that under hyperlipidemia, although foamy macrophages made clusters in the perivascular region, the cerebral microvessels did not develop atherosclerosis. On the other hand, in the other cerebral regions such as cerebral cortex, caudoputamen, globus pallidus, and substantia nigra, macrophages did not appear and microvessels retained normal shapes, but the fluorescent granular perithelial (in short, FGP) cells accompanied by these vessels contained a certain amount of lipids. That is, in the cerebral cortex and caudoputamen, lipid components are detected in FGP cells and microglia, while in the globus pallidus and substantia nigra, they are mainly localized in astrocytes. The reason why the astrocytes in such defined regions contain, specifically, a high quantity of lipid components remains unsettled. Axonal degenerations are often represented in thalamus, globus pallidus, and substantia nigra. On the other hand, in the specimens of Wild-type mice, lipid components were observed only in FGP cells, and the vascular architecture took a normal profile. Any lipid laden macrophages and the axonal degenerations could not be detected through the cerebral parenchyma. Furthermore, it is also a noticeable finding that immunohistochemically, the FGP cells express a positive reaction against the antibody of apo E in the Wild-type mice, but those of homozygous apo E deficient mice are immunonegative. FGP cells are not only provided with the scavenger receptor, but also contribute to the lipid metabolism in the brain.

The distribution of TM-316-associated surface antigen on polymorphonuclear leucocytes: an immunoelectron microscopic study.

It has been established that MoAb TM-316 recognizes an epitope on leucocytes and specifically inhibits the chemotactic behavior of leucocytes. In the present paper, the distribution of this epitope on the cell surface and in intracellular organelles was studied by immunoelectron microscopy. Leucocytes separated from the blood of healthy men and from synovial fluid from patients suffering from rheumatoid arthritis were used. They were fixed with a mixture containing paraformaldehyde, glutaraldehyde and picric acid. As the second antibody, goat anti-mouse IgM conjugated to 10 nm gold colloids was employed. In normal specimens, the epitope was found to some extent on the cytoplasmic membrane of neutrophilic leucocytes, but it was only sparsely distributed on eosinophilic and basophilic leucocytes. On activated neutrophilic leucocytes, obtained from the synovial fluid of rheumatoid arthritis patients, the immunolabeling was markedly increased. The number of sites where the epitope occurs on the surface of leucocytes is thus associated with the cell type, and also with the level of activation of the leucocytes. In order to investigate the processing of the antigen, the intracellular localization of the epitope in the neutrophilic leucocytes was also studied. The epitope recognized by TM-316 was also detected in/on the characteristic granules and Golgi stacks.

Tridimensional observation of fluorescent granular perithelial (FGP) cells in rat cerebral blood vessels.

The tridimensional appearance and distribution of FGP (fluorescent granular perithelial) cells was studied by means of light and scanning electron microscopy. In young rats they first appeared as hexagonal cells in that were closely associated; later they transformed into slender forms and were loosely arranged. Scanning electron microscope observation gave a general view of FGP cells, their globular vacuolated inclusions, and their hypertrophied protrusion into the luminal surface of blood vessels. The nodular protrusions may be related to the limitation of blood flow in small cerebral blood vessels.

An attempt to differentiate further between microglia and fluorescent granular perithelial (FGP) cells by their capacity to incorporate exogenous protein.

It seems established that under pathological conditions, microglia and blood monocytes (invading the cerebral parenchyma) behave as histiocytic cells in the central nervous system. However, it has not been clear whether or not phagocytic cells are present in normal cerebral tissue. Recently, we found a new type of cell having an uptake capacity for exogenous substance at the bifurcations of small cerebral vessels except for capillaries. According to Imamoto et al. (1982), ameboid microglia, a kind of precursor of microglia, appear at a perinatal stage and can incorporate exogenous material. In the present paper, the developmental sequences of ameboid microglia and the unique cells laden with fluorescent granules are compared at a light and electron-microscopic level. From this study, it is clear that ameboid microglia are already present in the corpus callosum at 5 days after birth and are potent in their uptake capacity for horseradish peroxidase (HRP). However, at 2 weeks, they transform into star cells and the capacity for incorporation diminishes markedly. The finding is also supported by the quantitative analysis of transformation of ameboid microglia. At 3 months, glial cells do not take the administered HRP under the present conditions. On the other hand, fluorescent granular perithelial (FGP) cells arise from a leptomeningeal tissue (pia mater) and become situated in the perivascular spaces. They are not clearly defined at 5 days, and their uptake capacity for HRP has not yet developed. At 2 weeks, the FGP cells take definite forms with several inclusion bodies, and their uptake capacity for HRP attains a certain degree. Often, they are located at bifurcations of small blood vessels. At 3 months, the FGP cells differentiate completely in appearance, and their pinocytotic capacity reaches a high level. Consequently, the FGP cells belong to a different type of cell from that of ameboid microglia in their developmental sequences and assume a principal role of scavenging waste products in normal cerebral tissue.

Distribution and number of fluorescent granular perithelial cells in coronal sections of rats cerebrum.

The fluorescent granular perithelial cells (F.G.P.) of rats aged 1 week to 2 years were observed under a light microscope to investigate intracellular granules and localization. This study showed that a marked proliferation of F.G.P. occurs within 3 weeks after birth and the total number remains constant for 2 years. The F.G.P. are mainly distributed in the gray matter, and are scarce in the white matter. The number and distribution of F.G.P. seems to reflect a difference of vascularization and function in different cerebral regions.