Ultrastructural cytochemical demonstration of peroxidase-positive monocyte granules: an additional method for studying the origin of mononuclear cells in encephalitic lesions

Ultrastructural characteristics of occluded perforating arteries in stroke-prone spontaneously hypertensive rats

We studied ultrastructurally cerebral perforating arteries in 60 stroke-prone spontaneously hypertensive rats (SHRSP), which were sequentially killed at 4-52 weeks of age before showing symptoms of stroke. Another 24 SHRSP were killed soon after they showed symptoms of cerebral infarction. The initial vascular lesions observed in the asymptomatic group included focal cytoplasmic necrosis in the outer layers of the media. This change progressed to widespread medial necrosis with time. In the infarction group, numerous monocytes were seen adhering to the endothelium of the arteries having advanced medial damage. Following the adherence of monocytes to the endothelium, large amounts of plasma components were visible in the arterial wall. The accumulation of the plasma components (especially fibrin) thickened the wall, narrowed the lumen, and resulted in occlusion. These results suggest that monocytes may affect the endothelium, perhaps disturbing the so-called blood-brain barrier to proteins. The monocytes may therefore be closely related to the occurrence of arterial occlusion with resultant cerebral infarction.

Immunocytochemical identification and quantitation of the mononuclear cells in the cerebrospinal fluid, meninges, and brain during acute viral meningoencephalitis

The mononuclear cells of the central nervous system (CNS) inflammatory response were characterized in cerebrospinal fluid (CSF), meningeal exudate, and brain parenchyma of mice 3-14 d after infection with Sindbis virus. The inflammatory infiltrate in CSF peaked and resolved before that of the parenchyma or meningeal exudate. Immunoperoxidase staining with monoclonal antibodies identified CSF inflammatory cells to be almost exclusively T cells, while inflammatory cells in the brain parenchymal perivascular cuffs and the meninges were a mixture of T cells, B cells, and macrophages. The percentage of B cells and macrophages increased at the later time points. Approximately 20% of CSF and 50% of the cells present early in the perivascular cuffs were not identified, suggesting that another subset of inflammatory cells may be present. We concluded that significant differences exist in the time course and cellular composition of the inflammatory responses in different compartments of the CNS during an acute viral infection.

Are resting and/or reactive microglia macrophages?

According to recent submicroscopic, cytokinetics, and functional (particularly cytoimmunologic) investigations, no relationship exists between "resting" microglia (the small argyrophilic cells appearing in undamaged brain tissue, first described by Rio Hortega) and "reactive" microglia (the argyrophilic cells appearing under pathologic conditions). While "resting" microglia are apparently cells of neuro-ectodermal origin, all observations tend to indicate that "reactive" microglia are derived from extravasated blood monocytes and should be called brain macrophages. In the intact brain parenchyma, no macrophages are demonstrable. Free subarachnoidal cells in the cerebrospinal fluid (CSF), perivascular cells, and epiplexus and/or supraependymal cells in the CSF-containing spaces of the normal central nervous system are cells of the mononuclear phagocyte system and must be considered as CSF macrophages. According to rough estimates, the normal adult central nervous system contains a maximum of 280,000 CSF macrophages.

Hematogenous origin of the inflammatory response in acute poliomyelitis

To determine the origin of the inflammatory response, and in particular the microglial rod cell response, in acute viral encephalitis, 4-week-old Swiss mice were injected with tritiated thymidine to label actively dividing cells prior to infection with the Lansing type 2 strain of poliovirus. As expected, the majority of polymorphonuclear and mononuclear leukocytes within the central nervous system perivascular infiltrates were shown to be hematogenous in origin. As early as 24 hours after infection, isotope-labeled cells having light histological and ultrastructural features consistent with microglia and microglial rod cells were identified within brain parenchyma and were shown to participate in neuronophagia and formation of glial nodules. Supraependymal and suprachoroidal cells were also shown to contain the label. However, neither endothelial cells nor pericytes contained label as determined by electron microscopy. These studies support a hematogenous origin for all cellular elements of the classic inflammatory response in viral infections of brain.

Dynamic aspects of glial reactions in altered brains

We investigated cellular reactions in altered brain with electron microscopy, 3H-thymidine autoradiography and immunohistochemistry. Comparing the results to those of classical studies with silver-impregnation method, following conclusions were obtained: 1. Full-blown macrophages, "amoeboid microglia", "rod cells" in acute viral encephalitis and "true" inflammatory cells in retrograde degeneration are derived from circulating mononuclear leukocytes which enter into brain parenchyma after the injuries. 2. Microglia, pericytes and other indigenous cells in brain parenchyma do not contribute to the macrophage formation. 3. Silver-impregnated resting microglia are definite cell group existing in the normal brain parenchyma. They are separate kind of cells from oligodendroglia or from mononuclear leukocytes. 4. In response to brain damage the resting microglia show marked swelling in the nucleus and cytoplasm, then, proliferate actively. After division they transform into reactive, fibrous astroglia. 5. Therefore, resting microglia are considered to be the reserve cells of fibrous astroglia.

Endogenous peroxidases: a morphological and functional marker to study inflammatory skin diseases

The visualization of peroxidase positive lysosomes by diaminobenzidine plus H2O2 allowed easy identification of neutrophils, eosinophils, monocytes and young tissue macrophages in 0.2 micrometer to 0.5 micrometer skin plastic sections of large surface area. Evaluation of the lysosomal functions of these phagocytic cells was greatly improved by the possibility of correlating observations on the same cell at light and electron microscopic levels.

Cytochemical markers for mononuclear phagocytes as demonstrated in reactive microglia and globoid cells

Several cytochemical characteristics of mononuclear phagocytes which are used as identifying markers were studied in reactive microglia from traumatically damaged brain tissue of guinea pigs and humans as well as in globoid cells from a child with familial globoid cell leukodystrophy (Krabbes' disease). The following cytochemical methods were used: acid phosphatase, lysozyme, peroxidase, alpha-naphthyl acetate esterase, alpha-naphthyl butyrate esterase, adenosine triphosphatase, and the periodic acid-Schiff reaction (PAS reaction). Distinct activity of almost all enzymes and the PAS reaction were demonstrable in reactive microglia and globoid cells. Peroxidase however could not be demonstrated in globoid cells. The similarity of the cytochemical characteristics for mononuclear phagocytes, reactive microglia, and globoid cells tends to indicate a common identity for these cell types. The lack of peroxidase in globoid cells may be due to a final maturation and differentiation after the monocyte stage.