Normal rat serum cytotoxicity against syngeneic oligodendrocytes. Complement activation and attack in the absence of anti-myelin antibodies

Complement C6 deficiency exacerbates pathophysiology after spinal cord injury

Historically, the membrane attack complex, composed of complement components C5b-9, has been connected to lytic cell death and implicated in secondary injury after a CNS insult. However, studies to date have utilized either non-littermate control rat models, or mouse models that lack significant C5b-9 activity. To investigate what role C5b-9 plays in spinal cord injury and recovery, we generated littermate PVG C6 wildtype and deficient rats and tested functional and histological recovery after moderate contusion injury using the Infinite Horizon Impactor. We compare the effect of C6 deficiency on recovery of locomotor function and histological injury parameters in PVG rats under two conditions: (1) animals maintained as separate C6 WT and C6-D homozygous colonies; and (2) establishment of a heterozygous colony to generate C6 WT and C6-D littermate controls. The results suggest that maintenance of separate homozygous colonies is inadequate for testing the effect of C6 deficiency on locomotor and histological recovery after SCI, and highlight the importance of using littermate controls in studies involving genetic manipulation of the complement cascade.

Extracellular Vesicles: Packages Sent With Complement

Cells communicate with other cells in their microenvironment by transferring lipids, peptides, RNA, and sugars in extracellular vesicles (EVs), thereby also influencing recipient cell functions. Several studies indicate that these vesicles are involved in a variety of critical cellular processes including immune, metabolic, and coagulatory responses and are thereby associated with several inflammatory diseases. Furthermore, EVs also possess anti-inflammatory properties and contribute to immune regulation, thus encouraging an emerging interest in investigating and clarifying mechanistic links between EVs and innate immunity. Current studies indicate complex interactions of the complement system with EVs, with a dramatic influence on local and systemic inflammation. During inflammatory conditions with highly activated complement, including after severe tissue trauma and during sepsis, elevated numbers of EVs were found in the circulation of patients. There is increasing evidence that these shed vesicles contain key complement factors as well as complement regulators on their surface, affecting inflammation and the course of disease. Taken together, interaction of EVs regulates complement activity and contributes to the pro- and anti-inflammatory immune balance. However, the molecular mechanisms behind this interaction remain elusive and require further investigation. The aim of this review is to summarize the limited current knowledge on the crosstalk between complement and EVs. A further aspect is the clinical relevance of EVs with an emphasis on their capacity as potential therapeutic vehicles in the field of translational medicine.

Cytotoxicity associated with prolonged room temperature storage of serum and proposed methods for reduction of cytotoxicity

Canine serum preserved at room temperature (25°C) for longer than 24h is known to exhibit significant cytotoxicity. This phenomenon is one of the major reasons for the failure of virus neutralization tests. In this study, a method for reducing this cytotoxicity was investigated by applying several treatments to dog, cat and human serum prior to room temperature storage. Additionally, the identity of the cytotoxic factor generated during room temperature storage was investigated. Heat-inactivation at 56°C or 65°C and the addition of protease inhibitor prior to storage were found to be effective for reducing cytotoxicity in the serum. Furthermore, heat-inactivation at 65°C reduced the cytotoxicity that was induced under room temperature storage. Several protein factors in serum were suspected to play a role in the observed cytotoxicity. According to this study, the membrane-attack-complex in serum was not involved in the cytotoxicity. This study provides useful information for development and improvement of cell culture and virus neutralization tests.

C1q, the classical complement pathway protein binds Hirano bodies in Pick's disease

Haematoxylin/Eosin staining was performed to screen for Hirano bodies from the temporal lobe including the hippocampus in 10 Pick's disease cases containing Pick bodies. Although the inclusions were confirmed in 9 out of 10 cases, only 4 out of 10 were particularly enriched with the eosinophilic bodies. These were subjected to immunostaining with anticomplement antibodies and astrocyte marker antiglial fibrillary acidic protein antibody and the HLA class II CR3/43 antibody to visualize microglia. An intraneuronal Hirano body was observed in one case that otherwise contained mainly the extracellular inclusions. In all cases, the extracellular Hirano bodies were seen lying adjacent to soma of neurons within CA1 region of the hippocampus. The extracellular Hirano bodies stained intensely with C1q, the first component of the classical pathway of activation but remained unreactive against antibodies to C4 and the C3 activation products (C3b and iC3b) and the alternative complement pathway component factor B. Hirano bodies also remained negative with the antiglial fibrillary acidic protein for astrocytes and HLA class II antibody CR3/43 for microglia. The results demonstrate that Hirano bodies have strong immunoreactivity to C1q; however, whether other complement components are associated with these inclusions remains to be further investigated.

Oligodendrocytes and the early multiple sclerosis lesion

There is little agreement among neuropathologists regarding the timing and nature of oligodendrocyte loss in multiple sclerosis (MS). This review describes changes that accompany acute oligodendrocyte loss in new lesions. Included is a description of the immunopathology of new lesions in 23 severe early cases selected from a bank of 300 MS autopsies. Oligodendrocytes in prephagocytic lesions exhibit cytopathic changes that include apoptosis of oligodendrocytes immunoreactive for caspase 3, phagocytosis of apoptotic oligodendrocytes, swelling of cells with abnormal nuclei, complement deposition, and lysis. These are nonspecific changes that provide no clue as to the cause of oligodendrocyte injury. Associated changes include the presence of enlarged immunoglobulin (IgG)(+) microglia and early macrophages, the presence nearby of a focus of inflammatory demyelination, an open blood-brain barrier, and the presence of rare CD8 T cells. Myelin contacted by IgG(+) macrophages is immunoreactive for complement but not for IgG. It is likely that macrophage activity in evolving white and gray matter plaques is scavenging activity directed at nonvital myelin secondary to oligodendrocytes loss. One feature of MS that is not understood is the extraordinarily close resemblance the disease shows pathologically to neuromyelitis optica (NMO), including that demyelination in both is secondary to a loss of caspase 3-positive apoptotic oligodendrocytes. These similarities raise the possibility that like NMO, MS is an autoimmune disease in which oligodendrocyte apoptosis is determined by injury to some other glial or mesenchymal component.

Central pontine myelinolysis: historical and mechanistic considerations

Central pontine myelinolysis (CPM) is a demyelinating condition affecting not only the pontine base, but also involving other brain areas. It usually occurs on a background of chronic systemic illness, and is commonly observed in individuals with alcoholism, malnutrition and liver disease. Studies carried out 25-30 years ago established that the principal etiological factor was the rapid correction of hyponatremia resulting in osmotic stress. This article reviews progress achieved since that time on its pathogenesis, focusing on the role of organic osmolytes, the blood-brain, barrier, endothelial cells, myelinotoxic factors triggered by osmotic stress, and the role of various factors that predispose to the development of CPM. These advances show great promise in providing novel therapeutic options for the management of patients afflicted with CPM.

Complement activation in autoimmune demyelination: Dual role in neuroinflammation and neuroprotection

Multiple sclerosis and its animal model experimental allergic encephalomyelitis are inflammatory demyelinating diseases of the central nervous system mediated by activated lymphocytes, macrophages/microglia and the complement system. Complement activation and the C5b-9 terminal complex contribute to the pathogenesis of these diseases through its role to promote demyelination. C5b-9 was also shown to protect oligodendrocytes from apoptosis both in vitro and in vivo. Our findings indicate that activation of complement and C5b-9 assembly plays a pro-inflammatory role in the acute phase, but may also be neuroprotective.

Effects of interferon-beta on oligodendroglial cells

The effect of interferon-beta (IFN-beta) for the treatment of multiple sclerosis (MS) is thought to be mediated by the modulation of immune cells. In addition, it has been shown that glial cells may be influenced by IFN-beta and a role during remyelination has been suggested. However, the mechanism is not yet clear and there are conflicting data. We have therefore systematically investigated proliferation, differentiation, toxicity, and cytoprotection of IFN-beta on oligodendroglia, both as a direct effect and mediated indirectly via other glial cells. Differentiation of oligodendrocyte progenitor cells (OPC) was significantly (p<0.01) inhibited by IFN-beta only when cultured in the presence with astrocytes and microglia. Proliferation was not changed, neither was IFN-beta toxic. There was no cytoprotective effect of IFN-beta on oligodendroglia injury induced by H2O2, NO, complement, or glutamate. Similarly, there was no cytoprotective effect mediated via treatment of astrocytes with IFN-beta. These data demonstrate that IFN-beta is neither toxic nor cytoprotective for oligodendrocytes. In summary, the only effect of IFN-beta was the inhibition of differentiation of OPC mediated indirectly via other glial cells. In vivo experiments will show how this effect may influence remyelination.

Effects of endotoxin administration and cerebral hypoxia-ischemia on complement activity and local transcriptional regulation in neonatal rats

It is not known whether up-regulation of complement components, either circulating or locally synthesized, contributes to an increased susceptibility to neonatal hypoxic-ischemic (HI) cerebral injury. Therefore, we tested the hypothesis that in neonatal rats subjected to a unilateral HI cerebral insult, prior administration of E. coli lipopolysaccharide (LPS) augments (1) complement-mediated serum hemolytic activity, and (2) C3 mRNA and C9 mRNA levels in hepatic and cerebral tissue. Pregnant rats were injected subcutaneously with sterile normal saline (NS) or 500 microg/kg of LPS on gestational days 18 and 19. Following birth, the pups received intraperitoneal injections of NS or 250 microg/kg of LPS on postnatal days 3 and 5. On postnatal day 7, each animal was subjected to ligation of the right common carotid artery followed by 2.5h of hypoxia (8% O(2)). At 3, 6,18, 24 and 48 h after hypoxia, the complement-mediated hemolytic activity of pooled serum was measured. Hepatic and cerebral C3 mRNA and C9 mRNA were quantified by qRT-PCR at 3, 6, and 18 h after HI. Serum hemolytic activity, hepatic C3 mRNA, and hepatic C9 mRNA were up-regulated after cerebral HI. LPS administration potentiated the effect of HI on serum hemolytic activity and increased cerebral C3 mRNA levels. Cerebral C9 mRNA was not detected and was not affected by HI, with or without the prior LPS administration. These observations support the theory that previously reported C9-mediated neurotoxicity following cerebral HI is induced by circulating, rather than locally synthesized C9.

Immunology of multiple sclerosis

Multiple sclerosis (MS) develops in young adults with a complex predisposing genetic trait and probably requires an inciting environmental insult such as a viral infection to trigger the disease. The activation of CD4+ autoreactive T cells and their differentiation into a Th1 phenotype are a crucial events in the initial steps, and these cells are probably also important players in the long-term evolution of the disease. Damage of the target tissue, the central nervous system, is, however, most likely mediated by other components of the immune system, such as antibodies, complement, CD8+ T cells, and factors produced by innate immune cells. Perturbations in immunomodulatory networks that include Th2 cells, regulatory CD4+ T cells, NK cells, and others may in part be responsible for the relapsing-remitting or chronic progressive nature of the disease. However, an important paradigmatic shift in the study of MS has occurred in the past decade. It is now clear that MS is not just a disease of the immune system, but that factors contributed by the central nervous system are equally important and must be considered in the future.

Activation of complement pathways after contusion-induced spinal cord injury

Previous studies have shown that a cellular inflammatory response is initiated, and inflammatory cytokines are synthesized, following experimental spinal cord injury (SCI). In the present study, we tested the hypothesis that the complement cascade, a major component of both the innate and adaptive immune response, is also activated following experimental SCI. We investigated the pathways, cellular localization, timecourse, and degree of complement activation in rat spinal cord following acute contusion-induced SCI using the New York University (NYU) weight drop impactor. Mild and severe injuries (12.5 and 50 mm drop heights) at 1, 7, and 42 days post injury time points were evaluated. Classical (C1q and C4), alternative (Factor B) and terminal (C5b-9) complement pathways were strongly activated within 1 day of SCI. Complement protein immunoreactivity was predominantly found in cell types vulnerable to degeneration, neurons and oligodendrocytes, and was not generally observed in inflammatory or astroglial cells. Surprisingly, immunoreactivity for complement proteins was also evident 6 weeks after injury, and complement activation was observed as far as 20 mm rostral to the site of injury. Axonal staining by C1q and Factor B was also observed, suggesting a potential role for the complement cascade in demyelination or axonal degeneration. These data support the hypothesis that complement activation plays a role in SCI.

Blockade of the C5a receptor fails to protect against experimental autoimmune encephalomyelitis in rats

Complement activation contributes to inflammation and tissue damage in human demyelinating diseases and in rodent models of demyelination. Inhibitors of complement activation ameliorate disease in the rat model antibody-dependent experimental autoimmune encephalomyelitis and rats unable to generate the membrane attack complex of complement develop inflammation without demyelination. The role of the highly active chemotactic and anaphylactic complement-derived peptide C5a in driving inflammation and pathology in rodent models of demyelination has been little explored. Here we have used a small molecule C5a receptor antagonist, AcF-[OPdChaWR], to examine the effects of C5a receptor blockade in rat models of brain inflammation and demyelination. C5a receptor antagonist therapy completely blocked neutrophil response to C5a in vivo but had no effect on clinical disease or resultant pathology in either inflammatory or demyelinating rat models. We conclude that C5a is not required for disease induction or perpetuation in these strongly complement-dependent disease models.

Complement component 9 activation, consumption, and neuronal deposition in the post-hypoxic-ischemic central nervous system of human newborn infants

The role of complement in neonatal hypoxic-ischemic brain injury is not known. Therefore, cerebral spinal fluid (CSF) and post-mortem cerebral tissue were analyzed to determine whether complement is activated and complement component 9 (C9) is deposited on neurons in the central nervous systems (CNS) of newborn infants who developed moderate to severe hypoxic-ischemic encephalopathy (HIE). Control CSF samples were obtained during routine evaluation for possible sepsis from infants who were not depressed at birth. In ELISA assays of CSF obtained from 16 infants with HIE, compared to CSF from 7 control infants, the mean concentration of terminal complement complexes was elevated and the mean C9 concentration was diminished. Immunofluorescence microscopy of post-mortem frozen brain tissue obtained from two infants who expired at 4-5 days of life after severe HIE revealed that activated C9 was deposited on cells in all lobes. Double label immunofluorescence microscopy demonstrated that nearly all of the C9-positive cells were neurons and essentially all of the neurons were C9-positive. Immunoperoxidase immunohistochemistry of formalin-fixed tissue also confirmed the presence of many C9-positive cells, particularly in the hippocampus. The C9-positive cells usually manifested morphology consistent with neurons, most of which contained fragmented nuclei. In summary, complement was activated in the CNS of newborn infants who developed moderate to severe HIE. C9 was deposited on neurons, including morphologically apoptotic neurons. Further investigations into a possible role of complement in the pathogenesis of neonatal hypoxic-ischemic cerebral injury are warranted.

The role of complement in neonatal hypoxic-ischemic cerebral injury

Complement activation participates in tissue injury after temporary loss of blood flow (ischemia-reperfusion injury). Recently reported evidence indicates that complement activation is a pathologic mechanism of injury in the post-hypoxic-ischemic neonatal brain. Therefore, recently developed complement inhibitors may find a role in the amelioration of neonatal hypoxic-ischemic cerebral injury. Further research is needed to better define the role of complement in human neonatal cerebral injury and to determine the neuroprotective effect and safety of pharmacologic agents designed to inhibit complement.

The administration of complement component C9 augments post-ischemic cerebral infarction volume in neonatal rats

To determine whether ischemic cerebral infarction is mediated in part by complement component C9, C9-deficient neonatal rats were subjected to unilateral cerebral ischemia. Brains were harvested 24 h later, stained with 2,3,5-triphenyl tetrazolium chloride, and cerebral infarct volumes were quantified by computer-based planimetry. Compared with buffer, prophylactic intraperitoneal (i.p.) administration of the complement inhibitors soluble complement receptor type 1 (sCR1), a molecular hybrid of sCR1 and the selectin inhibitor sialyl Lewis x (sCR1-sLex), or cobra venom factor did not affect the cerebral infarct volume. In contrast, i.p. human C9 (75 microg/g body weight) significantly increased the volume of infarct located 6 through 10 mm posterior to the frontal pole. Therefore, in the post-ischemic brain, C9 was neurotoxic and augmented the focal cerebral infarct volume.

Complement activated C4d immunoreactive oligodendrocytes delineate small cortical plaques in multiple sclerosis

C4d-immunoreactive complement-activated oligodendrocytes (C4d-CAOs) have been described in several neurodegenerative diseases but have not been studied in multiple sclerosis (MS). Here we report that such CAOs delineate miniature MS plaques of 300-500 mum diameter. They are devoid of myelin and are surrounded by a rim of activated microglia intermingled with the C4d-CAOs. Although C4d-immunostained periaxonal oligodendroglial processes are often swollen, the axons of passage appear undamaged and extend through the demyelinated plaque area. No immunostaining with other components of the complement cascade (C1q-C9) was observed in association with these miniature plaques. However, in large MS lesions, C1q-C9 immunoreactive fibers were present, indicating complete activation of the complement cascade in these more developed lesions. It is possible that the miniature plaques, bordered by C4d-CAOs, represent the earliest stage of plaque development, preceding even the larger, transient plaques frequently observed in serial MRI studies. The association of CAOs with miniature areas of demyelination suggests a direct attack on oligodendroglial cells by the early complement components as an initiating event in MS. Incomplete complement activation indicates that this step may be reversible, whereas full and persistent activation as observed in large MS lesions may lead to death of oligodendroglia with permanent axonal damage.

Neuroinvasion by pathogens: a key role of the complement system

Complement (C) is one of the most critical defence mechanisms of the innate immunity against cerebral infection by viruses, bacteria and fungi, with different molecular pathways contributing to the clearance of the invading pathogens. There is now compelling evidence that C proteins can be synthesized by brain cells in response to the infectious challenge and leading to cytotoxic and cytolytic activities against the harmful intruders. However, since there is also emerging evidence that uncontrolled C biosynthesis/activation can lead to brain inflammation with loss of neurons and oligodendrocytes, it is important to highlight that C may have adverse effects in infectious diseases of the CNS and induce profound tissue damage. The role of C in brain infection may even be more versatile. Many invading pathogens are not helpless against C attack and can use the membrane-bound C molecules to invade the host, either by binding directly or after decoration with C fragments. During budding viruses can acquire complement inhibitors from the host cell membrane and thus behave like 'Trojan horses' that are sheltered from the local innate immune response. Moreover, pathogens have evolved means of molecular mimicry with the expression of C inhibitor-like molecules to escape recognition and clearance by the C system. We herein provide a comprehensive and insightful review of the expression and the role of the C system in the brain. The three main focuses are: (i) C activation and lysis of pathogens in the brain; (ii) C-dependent neuroinvasion mechanisms (iii) uncontrolled C activation in inflamed CNS contributing to tissue damage.

Glial cells as targets for cytotoxic immune mediators

Oligodendrocytes and Schwann cells are the glia principally responsible for the synthesis and maintenance of myelin. Damage may occur to these cells in a number of conditions, but perhaps the most studied are the idiopathic inflammatory demyelinating diseases, multiple sclerosis in the CNS, and Guillain-Barré syndrome and its variants in the peripheral nervous system (PNS). This article explores the effects on these cells of cytotoxic immunological and inflammatory mediators: similarities are revealed, of which perhaps the most important is the sensitivity of both Schwann cells and oligodendrocytes to many such agents. This area of research is, however, characterised and complicated by numerous and often very substantial inter-observer discrepancies. Marked variability in cell culture techniques, and in assays of cell damage and death, provide artifactual explanations for some of this variability; true inter-species differences also contribute. Not the least important conclusion centres on the limited capacity of in vitro studies to reveal disease mechanisms: cell culture findings merely illustrate possibilities which must then be tested ex vivo using human tissue samples affected by the relevant disease.

Blood-brain barrier disruption and complement activation in the brain following rapid correction of chronic hyponatremia

In previous studies we developed a rat model in which demyelination is reproducibly produced following rapid correction of chronic hyponatremia and demonstrated that the development of demyelination in this model is strongly associated with NMR indices of blood-brain barrier (BBB) disruption. Because complement is toxic to oligodendrocytes, we evaluated the hypothesis that BBB disruption precipitated by correction of hypoosmolality is followed by an influx of complement into the brain, which then contributes to the demyelination that occurs under these conditions. We studied four groups of rats with immunocytochemical analysis using primary antibodies to IgG and the C3d split-fragment of activated complement: (1) normal rats; (2) rats in which hyponatremia was maintained for 7 days; (3) chronically hyponatremic rats in which the plasma [Na(+)] was rapidly corrected with hypertonic saline administration 20 h prior to perfusion; and (4) chronically hyponatremic rats in which the plasma [Na(+)] was rapidly corrected with hypertonic saline administration 5 days prior to perfusion. In normonatremic and uncorrected hyponatremic rats only background staining was observed in areas lacking a BBB and in blood vessel walls, whereas marked increases in IgG and C3d staining were seen in the brains of rats both 20 h and 5 days after rapid correction of hyponatremia. The staining intensity was significantly correlated with the degree of neurological impairment. These results provide evidence for functional BBB disruption following rapid correction of hyponatremia and support the hypothesis that complement activation may be involved in the pathogenesis of osmotic demyelination.

Spontaneous classical pathway activation and deficiency of membrane regulators render human neurons susceptible to complement lysis

This study investigated the capacity of neurons and astrocytes to spontaneously activate the complement system and control activation by expressing complement regulators. Human fetal neurons spontaneously activated complement through the classical pathway in normal and immunoglobulin-deficient serum and C1q binding was noted on neurons but not on astrocytes. A strong staining for C4, C3b, iC3b neoepitope and C9 neoepitope was also found on neurons. More than 40% of human fetal neurons were lysed when exposed to normal human serum in the presence of a CD59-blocking antibody, whereas astrocytes were unaffected. Significant reduction in neuronal cell lysis was observed after the addition of soluble complement receptor 1 at 10 microg/ml. Fetal neurons were stained for CD59 and CD46 and were negative for CD55 and CD35. In contrast, fetal astrocytes were strongly stained for CD59, CD46, CD55, and were negative for CD35. This study demonstrates that human fetal neurons activate spontaneously the classical pathway of complement in an antibody-independent manner to assemble the cytolytic membrane attack complex on their membranes, whereas astrocytes are unaffected. One reason for the susceptibility of neurons to complement-mediated damage in vivo may reside in their poor capacity to control complement activation.

Complement components of the innate immune system in health and disease in the CNS

The innate immune system and notably the complement (C) system play important roles in host defense to recognise and kill deleterious invaders or toxic entities, but activation at inappropriate sites or to an excessive degree can cause severe tissue damage. C has been implicated as a factor in the exacerbation and propagation of tissue injury in numerous diseases including neurodegenerative disorders. In this article, we review the evidence indicating that brain cells can synthesise a full lytic C system and also express specific C inhibitors (to protect from C activation and C lysis) and C receptors (involved in cell activation, chemotaxis and phagocytosis). We also summarise the mechanisms involved in the antibody-independent activation of the classical pathway of C in Alzheimer's disease, Huntington's disease and Pick's disease. Although the primary role of C activation on a target cell is to induce cell lysis (particularly of neurons), we present evidence indicating that C (C3a, C5a, sublytic level of C5b-9) may also be involved in pro- as well as anti-inflammatory activities. Moreover, we discuss evidence suggesting that local C activation may contribute to tissue remodelling activities during repair in the CNS.

Changes in cerebral blood flow and distribution associated with acute increases in plasma sodium and osmolality of chronic hyponatremic rats

The cause of the osmotic demyelination syndrome that follows too rapid correction of chronic hyponatremia (CHN) is unknown. Recently, we reported in CHN rats an association between blood-brain barrier (BBB) disruption occurring as early as 3 h into correction and subsequent demyelination. Given the changes in brain water and blood volume which occur during correction of CHN, we hypothesized that the same correction protocol that causes demyelination might alter cerebral blood flow (CBF) during correction, thereby possibly contributing to BBB disruption and demyelination. Ten CHN rats were given hypertonic sodium intraperitoneally and its effect on CBF was continuously monitored for 3 h by magnetic resonance flow imaging. Over the subsequent 3 h, plasma sodium rose from 110.8 to 127.6 mEq/liter (P < 0.001) but neither mean arterial blood pressure nor arterial CO(2) tension changed significantly. By 30 min, CBF increased by 50% in cortical and subcortical areas (P < 0.001) and remained elevated for the next 60 min. After 2 h, cortical flow was no longer elevated significantly and by 3 h it had returned to control values. Subcortical flow, however, significantly exceeded control values throughout the 3 h so that after 2 h the ratio of cortical to subcortical blood flow had fallen from 1.17 to 0.91 (P < 0.05). Although the mechanism by which increased plasma sodium and osmolality alters CBF is uncertain, the results suggest that changes in CBF may be part of a cascade of cerebrovascular disturbances including endothelial or parenchymal damage, mechanical events, metabolic disturbances, or cytokine release which eventually lead to BBB disruption and subsequent demyelination.

Oligodendroglia are protected from antibody-mediated complement injury by normal immunoglobulins ("IVIg")

High-dose intravenous immunoglobulin (IVIg) treatment has become a promising immune therapy that can modulate the immune system at several levels, including the complement cascade. In relation to inflammatory demyelinating disease, there is some clinical evidence for the suppression of disease activity by IVIg, while a role in promoting remyelination after experimental myelin damage has been described. Antibody and complement deposition have been implicated in the immune attack in some cases of multiple sclerosis (MS), and to investigate the mechanisms of action of IVIg, we studied the effect of IVIg using the model of complement-mediated cell injury on oligodendroglia in vitro. There was no effect on direct complement lysis of the oligodendroglial cell line CG4, but antibody-dependent complement damage was inhibited in a dose-dependent manner by IVIg. These results were confirmed with primary cultures of oligodendrocyte precursor cells (OPC) and oligodendrocytes. The addition of excess C1, C3, and C4 did not influence the inhibitory effect of IVIg, implying that binding of these complement components does not play a role, in contrast to other experimental models of complement damage. F(ab')2 immunoglobulin fragments were at least partially responsible for the effect. We conclude that IVIg may be protective in antibody-mediated complement injury of oligodendrocytes and their progenitors, and that this effect is likely to be mediated via antibody binding, rather than interference with complement activation. Inhibition of inflammatory mechanisms, as opposed to a direct effect on remyelinating cells, may underlie the role of IVIg in promoting myelin repair in experimental models.

Positive association between blood brain barrier disruption and osmotically-induced demyelination

Rapid correction of chronic hyponatremia can cause osmotic brain demyelination in animals and humans. Why demyelination develops is unknown, but blood brain-barrier disruption might expose oligodendrocytes to substances normally excluded from the brain. To test this hypothesis, chronic hyponatremia was induced and corrected using a new, reproducible rat model for producing osmotic brain demyelination. Blood brain barrier integrity was assessed by NMR imaging at either 3, 16 or 24 h during the first day of correction. Demyelination was determined histopathologically 5 - 6 days later. Of 96 rats studied, demyelination developed 5 - 6 days later in 37 rats, 89% of whom showed barrier disruption. In the 59 rats who did not develop demyelination, 45 (76%) had no barrier disruption. Thus, blood-brain barrier disruption during the first 24 h of correction was associated with a 70% risk of developing demyelination. By contrast, the risk of developing subsequent demyelination was only 8% when the barrier was intact. This strong association between barrier disruption and subsequent demyelination provides new insights into the role of blood brain barrier function in demyelinative disorders such as the osmotic demyelination syndrome and by extension to other demyelinative disorders such as multiple sclerosis.

Mechanisms of damage to myelin and oligodendrocytes and their relevance to disease

Oligodendrocytes synthesize and maintain myelin in the central nervous system (CNS). Damage may occur to these cells in a number of conditions, including infections, exposure to toxins, injury, degeneration, or autoimmune disease, arising both in the course of human disease and in experimental animal models of demyelination and dysmyelination; multiple sclerosis is the commonest human demyelinating disorder. Conventional classical accounts of the pathology of this and other myelin diseases have given great insights into their core features, but there remain considerable uncertainties concerning the timing, means and cause(s) of oligodendrocyte and myelin damage. At present, therapeutic efforts largely concentrate on immune manipulation and damage limitation, an approach that has produced only modest effects in multiple sclerosis. One reason for this must be the limited understanding of the mechanisms underlying cell damage - clearly, successful therapeutic strategies for preserving the oligodendrocyte-myelin unit must depend on knowledge of how oligodendrocyte damage and death occurs. In this review, mechanisms of oligodendrocyte and myelin damage are considered, and attempts made to relate them to disease processes, clinical and experimental. The hallmarks of different cell death processes are described, and oligodendrocyte-myelin injury by cellular and soluble mediators is discussed, both in vitro and invivo. Recent developments concerning the pathological involvement of oligodendrocytes in neurodegenerative disease are summarized. Finally, these neuropathological and applied neurobiological observations are drawn together in the context of multiple sclerosis.

No evidence for association of multiple sclerosis with the complement factors C6 and C7

Four genome screens in multiple sclerosis have been completed and each has identified evidence for linkage in the pericentromeric region of chromosome 5. This region encodes a number of candidate genes including those for the complement components C6, C7 and C9. We have used a multiplexed oligoligation assay (OLA) to test single nucleotide polymorphisms (SNPs) from the C6 and C7 genes for evidence of association with multiple sclerosis in our sibling pair families. There was no statistically significant difference in the allele frequencies of these polymorphisms in the index cases from our families when compared with locally derived controls. No evidence for transmission distortion was seen with any of the polymorphisms, or with the haplotype built from the three SNPs from the C7 gene. Despite offering themselves as potential candidates these complement genes appear not to confer susceptibility to multiple sclerosis.

Corpora-amylacea and the family of polyglucosan diseases

The history, characters, composition and topography of corpora amylacea (CA) in man and the analogous polyglucosan bodies (PGB) in other species are documented, noting particularly the wide variation in the numbers found with age and in neurological disease. Their origins from both neurons and glia and their probable migrations and ultimate fate are discussed. Their presence is also noted in other organs, particularly in the heart. The occurrence in isolated cases of occasional 'massive' usually focal accumulations of similar polyglucosan bodies in association with certain chronic neurological diseases is noted and the specific conditions Adult Polyglucosan body disease and type IV glycogenosis where they are found throughout the nervous system in great excess is discussed. The distinctive differences of CA from the PGB of Lafora body disease and Bielschowsky body disease are emphasised. When considering their functional roles, a parallel is briefly drawn on the one hand between normal CA and the bodies in the polyglucosan disorders and on the other with the lysosomal system and its associated storage diseases. It is suggested that these two systems are complementary ways by which large, metabolically active cells such as neurons, astrocytes, cardiac myocytes and probably many other cell types, dispose of the products of stressful metabolic events throughout life and the continuing underlying process of aging and degradation of long lived cellular proteins. Each debris disposal system must be regulated in its own way and must inevitably, a priori, be heir to metabolic defects that give rise in each to its own set of metabolic disorders.

Comparison of C1q-receptors on rat microglia and peritoneal macrophages

A comparison of the expression and ligand specificity of the C1q (first complement component) receptor on rat microglia and peritoneal macrophages was made. This revealed that radiolabelled C1q was competed from the peritoneal macrophages with intact C1q, and additively displaced by calf-skin collagen and purified C1q globular heads, suggesting the presence of at least two receptors. This was in contrast to microglia, where radiolabelled C1q was displaced with intact C1q and to a modest degree with collagen, but not with globular heads. Taken together, this implies that under these conditions, peritoneal macrophages and microglia both express a C1q receptor which binds to the collagen-like region, and that peritoneal macrophages additionally express a molecule which binds to the globular head of C1q. Analysis of the ligand bound by these cells reflected the differences observed in the competitive binding experiments, with the novel identification of naturally-occurring peptides from the globular head of C1q bound to the peritoneal macrophages, but not the microglia.

The structure and function of myelin oligodendrocyte glycoprotein

Myelin oligodendrocyte glycoprotein (MOG) is a quantitatively minor component of CNS myelin whose function remains relatively unknown. As MOG is an autoantigen capable of producing a demyelinating multiple sclerosis-like disease in mice and rats, much of the research directed toward MOG has been immunological in nature. Although the function of MOG is yet to be elucidated, there is now a relatively large amount of biochemical and molecular data relating to MOG. Here we summarize this information and include our recent findings pertaining to the cloning of the marsupial MOG gene. On the basis of this knowledge we suggest three possible functions for MOG: (a) a cellular adhesive molecule, (b) a regulator of oligodendrocyte microtubule stability, and (c) a mediator of interactions between myelin and the immune system, in particular, the complement cascade. Given that antibodies to MOG and to the myelin-specific glycolipid galactocerebroside (Gal-C) both activate the same signaling pathway leading to MBP degradation, we propose that there is a direct interaction between the membrane-associated regions of MOG and Gal-C. Such an interaction may have important consequences regarding the membrane topology and function of both molecules. Finally, we examine how polymorphisms and/or mutations to the MOG gene could contribute to the pathogenesis of multiple sclerosis.

Molecular cloning and characterization of RGC-32, a novel gene induced by complement activation in oligodendrocytes

Sublytic complement activation on oligodendrocytes (OLG) down-regulates expression of myelin genes and induces cell cycle in culture. Differential display (DD) was used to search for new genes whose expression is altered in response to complement and that may be involved in cell cycle activation. DD bands showing either increased or decreased mRNA expression in response to complement were identified and designated Response Genes to Complement (RGC) 1-32. RGC-1 is identical with heat shock protein 105, RGC-2 with poly(ADP-ribose) polymerase, and RGC-10 with IP-10. A new gene, RGC-32, that encodes a protein of 137 amino acids was cloned. RGC-32 has no homology with other known proteins, and contains no motif that would indicate its function. In OLG, the mRNA expression was increased by complement activation and by terminal complement complex assembly. RGC-32 protein was localized in the cytoplasm and co-immunoprecipitated with cdc2 kinase. Overexpression of RGC-32 increased DNA synthesis in OLGxC6 glioma cell hybrids. These results suggest that RGC-32 may play a role in cell cycle activation.

Neuropathology in multiple sclerosis: new concepts

Multiple sclerosis lesions are characterized by inflammation, demyelination and a variable degree of axonal loss. The patterns of inflammation in MS lesions are compatible with a T-lymphocyte mediated immune reaction. The formation of demyelinated plaques, however, seem to require additional immunological mechanisms. In this review evidence is discussed for a pathogenetic role of demyelinating antibodies, toxic macrophage products, cytotoxic T-cells as well as metabolic disturbances of oligodendrocytes. It is suggested that the pathological heterogeneity regarding the patterns and extent of demyelination, remyelination and axonal loss may be the outcome of variable dominant immunopathogenetic mechanisms in different multiple sclerosis patients.

Multiple sclerosis: in situ evidence for antibody- and complement-mediated demyelination

We describe a case of multiple sclerosis characterized by deposition of immunoglobulin and complement in the areas of active demyelination. This was particularly evident for the C9neo antigen, which is a marker for the activated lytic complement complex and was exclusively deposited in the areas of active myelin destruction. In addition, macrophages in the lesions contained degradation products that were immunoreactive for myelin antigens, immunoglobulins, and C9neo antigen. Destruction of myelin sheaths was associated with incomplete loss of oligodendrocytes in the active areas and reappearance of oligodendrocytes with remyelination in the inactive plaque center.

The expression of complement regulatory proteins by adult human oligodendrocytes

In multiple sclerosis, infiltrating T lymphocytes and perivascular microglia may initiate demyelinating lesions, but a role for antibody and complement in the ensuing inflammatory damage to myelin and oligodendrocytes is likely. In most tissues, ubiquitously expressed complement regulatory proteins prevent autologous destruction, protecting host cells from the powerful cytolytic activity of activated complement. We have studied the surface expression of a comprehensive range of complement regulatory proteins by live adult human oligodendrocytes in vitro. Only DAF of the activation pathway regulators was expressed, not CR1 or MCP. Of the membrane attack pathway regulatory proteins, HRF was not expressed, while substantial heterogeneity of CD59 expression by oligodendrocytes was found. Clusterin expression was not found. A relative deficiency of protective complement regulatory proteins on human oligodendrocytes may contribute to their selective damage in multiple sclerosis.

HIV-gp120 affects the functional activity of oligodendrocytes and their susceptibility to complement

The aim of this study was to assess whether the HIV protein gp120 can induce direct or/and indirect damage to oligodendrocytes (OL). Using highly purified cultures of rat OL, we report that gp120 binds to OL and induces functional alterations in these cells. Indeed, the percentage of cells expressing myelin basic protein (MBP) and the levels of all four MBP isoforms were substantially reduced after a 3-day treatment with 10 nM gp120. As gp120 depressed the ability of OL to reduce the tetrazolium salt MTT (a sign of mitochondrial impairment), the alteration of MBP production may be a consequence of decreased metabolic activity. The above effects were accompanied by a small increase in the number of apoptotic nuclei (from 4.3% in controls to 17.6% in cells treated for 3 days with gp120). As complement can lyse OL and gp120 is known to activate complement, we also studied the interaction between these two factors using OL cultures. The viral protein potentiated (by about 25%) the lytic effect of complement, when administered to the cultures 5 hr after complement, and depressed it (by about 30-40%), when added 5 hr before complement. Heat denaturation and anti-gp120 antibodies prevented the direct effect of gp120 on OL, but did not influence the interactions between gp120 and complement. Some gp120 non glycosylated peptides (V3 loop, 254-274 and 415-435 peptides) mimicked the ability of gp120 to antagonize the lytic effect of complement, but not that of potentiating complement lytic activity. In conclusion, our study indicates that gp120 can alter OL functional activity directly and can interfere with OL susceptibility to complement mediated lysis.

Terminal complement complexes induce cell cycle entry in oligodendrocytes through mitogen activated protein kinase pathway

Sublytic complement attack through C5b-9 assembly induces oligodendrocytes (OLG) to express proto-oncogenes and to enter the cell cycle from resting G0/G1 phase to S phase. We have investigated whether cell cycle induction by C5b-9 is mediated by mitogen activated protein kinase (MAPK) pathway in OLG. C5b-9 but not C5b6 induced activation of both ERK1 and c-jun NH2 terminal kinases 1 (JNK1) in OLG. The increased ERK1 and JNK1 activities are transient, reaching a maximum around 20 min following exposure to C5b-9. Activation of Raf-1 and MEK1, upstream kinases of ERK1, was shown by increased Raf-1 kinase activity in anti-Raf-1 immunoprecipitates of OLG treated with C5b-9 and ERK1 activity that can be inhibited by PD098,059, a specific MEK1 inhibitor. Requirement for the ERK1 pathway in DNA synthesis was then evaluated using PD098,059. Enhanced DNA synthesis induced by serum complement was completely abolished when OLG were pretreated with PD098,059. On the other hand, c-fos mRNA expression induced by complement was inhibited only 50% by PD098,059, while the c-jun mRNA level was not affected by this MEK1 inhibitor. Interestingly, p70 S6 kinase, an important ribosomal kinase in mitogenesis, was also activated by C5b-9. These findings indicated that the MAPK pathways appears to play a major role in inducing OLG to enter the S phase of the cell cycle from the resting G1/G0 phase.

The controversy surrounding the pathogenesis of the multiple sclerosis lesion

The main issues in multiple sclerosis research revolve around four fundamental questions. (1) What initiates the disease-that is, autoimmune T cells, a virus, or a toxin? (2) Is the inflammatory response primary to the development of demyelination, or is it a secondary response to injury? (3) Is the oligodendrocyte, the myelin-producing cell, the primary target? (4) How can myelin repair be promoted? This review focuses on the controversies revolving around these important questions. Although many investigators believe that T-cell receptors on CD4+ cells interact with myelin antigens to initiate an inflammatory cascade that leads to myelin destruction, others maintain that a viral agent may have a direct or indirect role in the pathogenesis of multiple sclerosis. The concept that the immune system contributes to the tissue destruction in multiple sclerosis is generally accepted; however, the debate about cause versus consequence of the pathologic process remains unresolved, as does the identification of the initial event or focus of the damage. Electron microscopic studies have disclosed evidence of remyelination (albeit often incomplete) in lesions of multiple sclerosis. Enhanced understanding of the factors limiting remyelination could help formulate strategies to promote repair. By innovative experimental design and application of available molecular techniques, the answers to these questions may provide insights on how to prevent or treat multiple sclerosis.

Binding of complement component Clq to myelin oligodendrocyte glycoprotein: a novel mechanism for regulating CNS inflammation

Myelin oligodendrocyte glycoprotein (MOG) is a myelin-specific protein restricted to the central nervous system (CNS). While MOG is considered a putative autoantigen in MS, its function(s) in myelin is unknown. As CNS myelin is able to activate the classical complement pathway, it must contain a Clq-binding/activating protein but the identity of this protein has not been reported. The data in this paper clearly demonstrate that MOG specifically binds Clq in a dose-dependent and saturating manner. This calcium-dependent interaction is mediated by the extracellular immunoglobulin-like domain of MOG. This MOG domain contains an amino acid motif similar to the core Clq-binding sequence previously identified in IgG antibodies. Purified MOG also inhibited the antibody-dependent lysis of RBC by complement. Taken together, these results demonstrate that MOG binds Clq near the IgG binding site and may be the protein responsible for complement activation in myelin. This direct interaction between a myelin-specific protein and Clq has significant implications for CNS inflammation and could be particularly important in demyelinating diseases such as multiple sclerosis.

Complement activation in the central nervous system following blood-brain barrier damage in man

The central nervous system (CNS) is virtually isolated from circulating immunological factors such as complement (C), an important mediator of humoral immunity and inflammation. In circulation, C is constantly inhibited to prevent attack on host cells. Since a host of diseases produce an abnormal blood-brain/cerebrospinal fluid (blood-brain/CSF) permeability allowing C protein extravasation, we investigated if C activation occurs in CSF in vitro and in CNS in vivo during subarachnoid hemorrhage (SAH) or brain infarction. After SAH (n = 15), the terminal complement complex (TCC) concentration on days 0 to 2 was higher in the CSF, 210 +/- 61 ng/ml, than in the plasma, 63 +/- 17 ng/ml, but null in the CSF of controls (n = 8) or patients with an ischemic stroke (n = 7). TCC was eliminated from the CSF after SAH (24 +/- 10 ng/ml on days 7 to 10). Incubation of normal human CSF with serum in vitro also activated the terminal C pathway. In 10 fatal ischemic brain infarctions, immunohistochemical techniques demonstrated neuronal fragment-associated deposition of C9 accompanied by neutrophil infiltration. We conclude that the C system becomes activated intrathecally in SAH and focally in the brain parenchyma in ischemic stroke. By promoting chemotaxis and vascular perturbation, C activation may instigate nonimmune inflammation and aggravate CNS damage in diseases associated with plasma extravasation.

Distinct patterns of multiple sclerosis pathology indicates heterogeneity on pathogenesis

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system. The hallmark of its pathology is the demyelinated plaque with reactive glial scar formation. However, a detailed analysis of the patterns of demyelination, oligodendroglia cell pathology and the reaction of other tissue components suggests that the pathogenesis of myelin destruction in this disease may be heterogeneous. In this review we present a new classification scheme of lesional activity on the basis of the molecular composition of myelin degradation products in macrophages. When these criteria are used, different patterns of demyelination can be distinguished, including demyelination with relative preservation of oligodendrocytes, myelin destruction with concomitant and complete destruction of oligodendrocytes or primary destruction or disturbance of myelinating cells with secondary demyelination. Furthermore, in some cases a primary selective demyelination may be followed by a secondary oligodendrocyte loss in the established lesions. Finally, some extraordinarily severe conditions may result in destructive lesions with loss of myelin, oligodendrocytes, axons and astrocytes. This heterogeneity of plaque pathology is discussed in the context of recent experimental models of inflammatory demyelination, which show that different immunological pathways may lead to the formation of demyelinated plaques that reveal the diverse structural aspects described above. Our data indicate, that the demyelinated plaques of multiple sclerosis may reflect a common pathological end point of a variety of different immunological mechanisms of myelin destruction in this disease.

Ciliary neurotrophic factor selectively protects human oligodendrocytes from tumor necrosis factor-mediated injury

Oligodendrocytes (OLs) and their myelin membranes are the apparent injury targets in the putative human autoimmune disease multiple sclerosis. The basis for this selective injury remains to be defined. OLs in vitro have been shown to be susceptible to both tumor necrosis factor (TNF) and non-TNF-dependent immune effector mechanisms. The former involves initial nuclear injury (apoptosis); the latter, when mediated by activated T cells, involves initial cell membrane injury (lysis). In the current study, we determined whether human adult CNS-derived OLs could be protected from the above immune effector mechanisms by selected neurotrophic factors (CNTF, BDNF, NGF, NT-3, and NT-4/5) or cytokines demonstrated to protect from human or experimental autoimmune demyelinating diseases (beta-interferon [IFN], IL-10, and TGF-beta). Nuclear injury was assessed in terms of DNA fragmentation using a DNA nick-end-labelling technique; cell membrane injury was assessed by lactate dehydrogenase or chromium 51 release. MTT and cell counting assays were used to assess cell viability and cell loss, respectively. Amongst the neurotrophic factors and cytokines tested, only CNTF significantly protected the OLs from TNF-mediated injury. CNTF also protected the OLs from serum deprivation-induced apoptosis. CNTF, however, did not protect the OLs from injury induced by activated CD4+ T cells. CNTF also did not protect human fetal cortical neurons from serum deprivation or TNF-induced DNA fragmentation, nor did it protect the U251 human glioma cell line from DNA fragmentation induced by a combination of TNF and reduced serum concentration in the culture media. Our results indicate that potential protective effects of neurotrophic factors or cytokines on neural cell populations can be selective both for cell type involved and mechanism of immune-mediated injury. CNTF is the protective factor selective for nuclear-directed injury of OLs.

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.

A functional role for corpora amylacea based on evidence from complement studies

Few theories have been advanced for the production of corpora amylacea (CA) by the normal ageing brain and by the CNS under various neurological conditions. Proteins derived from neurons and oligodendrocytes are found in CA and to understand their origins brain tissue from patients with Alzheimer's disease (AD), multiple sclerosis (MS) and Pick's disease (PD) were tested for complement activity. All CA were immunopositive for antisera to classical pathway-specific components, the activation products C3d and the terminal complement complex (TCC), the C3 convertase regulator membrane cofactor protein (MCP) and the fluid phase regulators S-protein and clusterin. CA were immunonegative for the alternative complement pathway proteins and the complement regulators, decay accelerating factor (DAF) and CD59. Western immunoblotting of isolated solubilized CA from the same tissues demonstrated a weak band for MCP but TCC was more easily shown by immunoprecipitation. A filamentous fringe around CA, probably of astrocytic origin, was also immunopositive for complement factors. CA consist of an inert mucopolysaccharide matrix encasing ubiquitinated proteins, resulting from death of and damage to neurons, myelin and oligodendrocytes. A function of CA, therefore, could be to prevent the recognition of these immunogenic proteins by lymphocytes and microglia and thus protect the CNS from further injury.

Mechanisms of damage and repair in multiple sclerosis--a review

Pathological features of MS include perivascular inflammation and demyelination with oligodendrocyte loss; in addition, attempts at remyelination are often unsuccessful and may culminate in astrocytic scarring. One approach to investigating the biological principles underlying these processes is to use in vitro systems to analyse single-cell behaviour as well as cell-cell interactions. This paper reviews such data concerned with cell injury and repair which illuminate both demyelination and remyelination. In tissue culture oligodendrocytes are susceptible to injury via cell-mediated and humoral mechanisms. Substances including complement and tumour necrosis factor are capable of killing rat oligodendrocytes in vitro; surface complement activation also initiates a number of intracellular processes within oligodendrocytes as well as providing ligands for phagocytic interactions. The reasons for oligodendrocyte complement activation are discussed, but it appears that species differences exist when extrapolating these data to humans. Myelination and remyelination can also be studied both in vitro and in vivo using defined cell populations. Results from these studies may eventually help to explain some pathological features of MS, including astrocytosis and factors governing the limits of remyelination.

Effect of rapid correction of hyponatremia on the blood-brain barrier of rats

Brain demyelination sometimes follows rapid correction of hyponatremia, especially if the hyponatremia is chronic. During correction brain water decreases and the brain shrinks. The present study examined whether such shrinkage might be sufficient to disrupt the tight junctions of the blood-brain barrier. Barrier intactness was evaluated using magnetic resonance imaging and intravenous gadolinium contrast administration. Hypertonic saline infusion rapidly increased the plasma sodium concentration and caused barrier disruption more frequently in chronic than in acute hyponatremic rats. Similar increases in plasma sodium concentration did not disrupt the barrier in normonatremic rats. The disruption appeared to be due to altered plasma osmolality since infusion of hypertonic mannitol, which raised plasma osmolality without changing the plasma sodium concentration, disrupted the barrier in hyponatremic but not normonatremic rats. Moreover, the osmotic threshold for barrier disruption was lowest in chronic hyponatremia, intermediate in acute hyponatremia, and highest in normonatremia. The greater susceptibility to osmotic disruption in chronic hyponatremia suggests that blood-brain barrier disruption may play a significant role in causing the demyelination sometimes found following too rapid correction of hyponatremia, possibly through exposure of oligodendrocytes to plasma macromolecules such as complement.

Growth factors fail to protect rat oligodendrocytes against humoral injury in vitro

CNS growth factors protect neurons and glia against a wide variety of insults in vitro and in vivo by mechanisms which include buffering toxic rises in intracellular calcium. Cytosolic calcium elevation also plays a key role in complement injury, but the possibility that growth factors protect against antibody-mediated complement attack has not hitherto been addressed. In multiple sclerosis, antibodies and complement appear to contribute to the selective targeting and damage of oligodendrocytes and myelin. Here we have investigated the possibility that growth factors active in oligodendrocyte development and differentiation might protect these cells against injury mediated by antibody and complement in vitro. None was found to be protective.

Physiology and pathophysiology of complement: progress and trends

The complement system comprises a family of at least 20 plasma and membrane proteins that interact in a tightly regulated cascade system to destroy invading bacteria and prevent the deposition of immune complexes in the tissues. This brief review addresses the basic mechanisms of complement activation and control and describes the active fragments produced during complement activation. The biological importance of the complement system is amply illustrated in patients with complement deficiencies, who are susceptible to bacterial infections and immune complex diseases. The involvement of complement in other immunological diseases is an expanding area of clinical research, supported by the development of new assays for the identification of complement activation. This area is discussed here with particular reference to neurological diseases. A promising new prospect involves the use of complement inhibitory molecules in therapy of complement-mediated disease and this exciting area is also discussed. Novel physiological roles of complement also are being revealed and new evidence that complement and complement receptors play an important role in reproduction is summarized. It is hoped that this brief overview will convey some of the enthusiasm currently pervading research in this underappreciated area of immunology.

Cerebrospinal fluid concentrations of the complement MAC inhibitor CD59 in multiple sclerosis and patients with other neurological disorders

Rodent oligodendrocytes have a unique susceptibility among glia to the lytic effects of complement, due in part to a deficiency in CD59 (protectin), a key surface inhibitor of the complement membrane attack complex (MAC). The possibility that shedding of CD59 by human oligodendrocytes contributes to complement-mediated oligodendrocyte injury in inflammatory demyelinating disease has been investigated by estimating levels of CD59 in cerebrospinal fluid samples from 12 patients with demyelinating disease of the central nervous system and 13 with other neurological diseases. No significant differences were found between patients and controls, or between patients with active and those with clinically inactive demyelinating disease, providing no direct support for oligodendrocyte shedding of CD59 in multiple sclerosis.