Inflammatory central nervous system demyelination: correlation of magnetic resonance imaging findings with lesion pathology.

Magnetic resonance imaging (MRI) is widely used to evaluate and monitor disease activity in inflammatory demyelinating central nervous system (CNS) diseases such as multiple sclerosis. The present study aimed at correlating MRI findings with histological parameters in 6 cases of biopsy-proven inflammatory demyelination of the CNS. The earliest stages of demyelinating activity manifested as almost isointense lesions with a massive gadolinium-DTPA (Gd-DTPA) enhancement in T1-weighted scans. In T2-weighted scans, early active lesions formed a border of decreased intensity compared with the lesion center and the perifocal edema. The morphological correlate of this pattern in our patients was activated macrophages in the zone of myelin destruction at the plaque border. Late active lesions were hypointense in T1 and hyperintense in T2 scans. Inactive demyelinated and remyelinating lesions were hyperintense in T2 scans and enhanced inhomogenously after Gd-DTPA application. T1 scans revealed major differences in the degree of hypointensity that correlated with the extent of axonal damage, extracellular edema, and the degree of demyelination or remyelination.

Anti-inflammatory treatment influences neuronal apoptotic cell death in the dentate gyrus in experimental pneumococcal meningitis.

Apoptotic neuronal death and the increase of neuron-specific enolase (NSE) in cerebrospinal fluid (CSF) were studied in a rabbit model of experimental pneumococcal meningitis after treatment with antimicrobial (ceftriaxone) and antiinflammatory agents (dexamethasone, monoclonal antibodies against the beta-subunit of beta 2-integrins [anti-CD18 mAb]). Twenty-four hours after infection, apoptotic cell death was found solely in the granular cell layer of the dentate gyrus. Neurons with DNA fragmentation were quantified with the in situ tailing (IST) reaction. Dexamethasone and anti-CD18 mAb inhibited the NSE increase in CSF significantly (p = 0.003, p = 0.011). After administration of dexamethasone the density of apoptotic neurons was significantly higher than in control animals receiving only ceftriaxone (p = 0.044). The median of the density of apoptotic neurons was lower in the dentate gyrus in animals receiving anti-CD18 mAb and ceftriaxone vs those receiving only ceftriaxone, although the difference did not reach statistic significance (p = 0.058). In conclusion, apoptotic cell death occurs in the dentate gyrus during the early phase of bacterial meningitis. The extent was influenced by antiinflammatory therapy. The systemic administration of glucocorticoids increased the quantity of apoptotic neurons in the dentate gyrus but reduced overall neuronal damage as indicated by low levels of NSE concentration in CSF.

Evidence for neuronal apoptosis in pontosubicular neuron necrosis.

Pontosubicular neuron necrosis (PSN) is characterized by acute neuronal death in the subiculum and the pons occurring in a circumscribed perinatal period. The morphological changes in PSN are quite similar to those described during apoptosis, a form of programmed cell death. Morphological re-evaluation of the lesions by light and electron microscopy revealed the typical changes of apoptosis with condensed basophilic nuclei and the formation of apoptotic bodies. By analysing DNA fragmentation in situ with a recently established technique, we were able to show that neuronal death in PSN is apoptotic. The demonstration of DNA fragmentation by the in situ tailing technique was reliable in the human autopsy material used in this study and was only slightly affected by autolysis or formalin fixation. The subiculum and the pons are shown to be susceptible to apoptosis at different times during development. PSN thus provides a model in which the process of nerve cell apoptosis in the developing human central nervous system can be studied.

Mechanisms of macrophage recruitment in Wallerian degeneration.

Monocytes/macrophages are important effector cells in myelin removal during Wallerian degeneration. Experiments with the mouse mutant C57BL/Ola revealed prolonged axonal survival and reduced phagocytic cell recruitment after nerve transsection. In the present study, we compared the course of Wallerian degeneration in peripheral nerves of C57BL and C57BL/Ola mice in vivo and in vitro. In vivo experiments confirmed earlier investigations describing a delayed degeneration in the C57BL/Ola mutant compared with C57BL mice which were used as control animals without abnormal degeneration. Quite different results were seen in experiments in vitro: degenerating nerve segments of C57BL/Ola mice revealed pronounced axonal breakdown even in the absence of non-resident phagocytic cells. There was no difference in vitro compared with degenerating nerves from C57BL mice. The differences observed between the in vivo and in vitro situations suggest that axonal breakdown plays an important role in the initiation of macrophage recruitment to degenerating peripheral nerves.

The membrane attack complex of complement mediates peripheral nervous system demyelination in vitro.

The present study used cocultures of rat dorsal root ganglia (DRG) and peritoneal macrophages to define the role of activated complement components during demyelination. The complement cascade was activated in vitro by treatment of the cultures with natural rat serum and lipopolysaccharides. Complement activation was examined by detection of the membrane attack complex of complement (MAC) with an antibody directed against rat C5-9. Detection of MAC in vitro by immunoelectron microscopy was associated with morphological changes of the myelin sheath. The sheath's regular structure was disrupted. Myelin lamellae were split and showed signs of decompaction. These changes were followed by a selective macrophage attack on myelin sheaths resulting in demyelination. Schwann cell viability was not affected by complement activation. Axons and sensory ganglion cells also survived this attack. The specificity of the complement effect was tested in experiments using treatment regimens with natural rat serum or lipopolysaccharides alone. In these experiments, no morphological changes of the myelin sheath were observed as well as no macrophage attack on myelin.

Dorsal root ganglia cocultured with macrophages: an in vitro model to study experimental demyelination.

The present investigation introduces an in vitro model to study macrophage properties during demyelination. Rat dorsal root ganglia (DRG) were cultured for obtaining myelinated peripheral nerve fibers. These cultures were exposed to non-resident macrophages. In untreated control cultures, there was no indication of myelin removal by the added macrophages. DRG were exposed to enzymatically generated oxygen radicals using the xanthin/xanthin oxidase or the glucose/glucose oxidase system. Assessment of Schwann cell viability and ultrastructural morphology revealed different patterns of cell cytotoxicity and morphological changes in different experiments. High concentrations caused complete tissue necrosis of the DRG, while low concentrations did not affect either cell viability or ultrastructural morphology. Under intermediate experimental conditions, oxygen radicals caused non-lethal Schwann cell damage leading to Schwann cell retraction and myelin sheath rejection. Myelin lamellae were disrupted and decompacted. These changes were followed by a selective macrophage attack on myelin sheaths, resulting in demyelination. Axons, Schwann cells and sensory ganglion cells survived this attack. The specificity of the oxygen radical effects was tested in experiments using the oxygen radical scavengers catalase and superoxide dismutase. Catalase prevented the described effects on cell morphology and subsequently blocked demyelination by non-resident macrophages.

Oligodendrocytes in the early course of multiple sclerosis.

The neuropathology of demyelinating lesions in multiple sclerosis was studied in specimens obtained by diagnostic needle biopsy during early stages of the disease. The lesions were characterized by a chronic inflammatory reaction dominated by lymphocytes and macrophages, plaque-like demyelination, and astroglial sclerosis. Oligodendrocytes within the lesions were studied by immunocytochemistry using antibodies against various myelin and oligodendroglia components. The expression of messenger RNA for proteolipid protein was determined by in situ hybridization. Our studies revealed that myelin-oligodendrocyte glycoprotein is a sensitive and reliable marker for identification of oligodendrocytes in demyelinated plaques. The results suggest that in the early course of the disease in some patients, oligodendrocytes may largely be preserved, whereas in others oligodendroglial loss is pronounced. Loss of oligodendrocytes was only marginally related to the stage of demyelinating activity within the lesions. These findings indicate that the pathogenesis of demyelination may vary within different multiple sclerosis patients.

Macrophage properties during peripheral nervous tissue rejection in vitro.

The present study introduces an in vitro model of xenogeneic peripheral nerve rejection to analyze the role of macrophages in this complex immunological situation. Nerve-sensitized mouse peritoneal exudate cells were co-cultured with rat peripheral nerve segments. The cultured rat nerve segments were fulminantly rejected in vitro by the co-cultured mouse peritoneal cell population. The massive tissue destruction included Schwann cell damage and was quite distinct from basic myelin phagocytosis observed during Wallerian degeneration in earlier experiments. The nerve-sensitized peritoneal exudate consisted of macrophages and T-cells. Antibody depletion experiments were performed to analyze T-lymphocyte effects in this model. Fulminant tissue rejection depended on the presence of T-lymphocytes in the culture medium. Their presence at the immediate site of tissue rejection, however, was not required. Further experiments were aimed at defining the role of T-cell-derived mediators during in vitro rejection. Depletion experiments using a panel of antibodies to cytokines revealed a critical involvement of IL-2, IL-3, IL-4, IL-6 and interferon-gamma in the induction of tissue rejection in vitro. Fulminant tissue rejection in vitro depended on the interaction of these cytokines with macrophages. The participation of macrophage surface receptors was studied in another series of experiments. The macrophage complement receptor type 3 was shown to be critically involved in the phagocytic attack during rejection. Antibodies to MHC class II antigens also abolished fulminant in vitro rejection, indicating that continuous antigen presentation is required in this process.

Acute demyelinating disease. Classification and non-invasive diagnosis.

Five young patients are described with biopsy-proven acute demyelinating disease. Two cases are classified as Schilder's disease, a particular childhood form of multiple sclerosis (MS) with atypical clinical manifestation, normal or atypical CSF-findings and large bilateral lesions in magnetic resonance imaging (MRI). Two further cases presented with a fulminant bout of MS with typical clinical picture and CSF-findings; they are classified as Marburg's disease. The last case was an acute second bout of classical MS. The biopsy seemed to be justified in 4 cases, but unnecessary in the last case. Localized proton magnetic resonance spectroscopy (MRS) performed in one case allowed us to examine the focal cerebral abnormalities directly and non-invasively. The spectra revealed a pattern typical of acute demyelination suggesting potential for a replacement of biopsy in the future.

TNF-alpha suppresses CR3-mediated myelin removal by macrophages.

Mononuclear cells of the monocyte/macrophage system play an important role in myelin ingestion during Wallerian degeneration. The present in vitro study clarifies the role in this process of two macrophage-secreted cytokines, TNF-alpha and interleukin-1. Treatment with TNF-alpha massively reduced the amount of myelin ingested by macrophages via their complement receptor type 3 (CR3). Anti-TNF-alpha antibodies reversed the effect. Immunofluorescence of macrophages indicated that TNF-alpha caused a reduced expression of the CR3 by phagocytic cells. Further experiments revealed an interaction of TNF-alpha with its receptor on the macrophage cell membrane. Interleukin-1 had no effect on myelin ingestion in the in vitro system used in these experiments.