Antibody-independent complement activation by myelin via the classical complement pathway

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.

Anti-metastatic effect of polysaccharide isolated from Colocasia esculenta is exerted through immunostimulation

In the present study, an edible corm of the plant Colocasia esculenta, commonly known as Taro was extracted with cold water (4˚C). Finally, 10.44 g (1.04%) of the crude polysaccharide (Taro-0) was obtained from Taro. The purified active compound (Taro-4-I) was isolated using DEAE-Sepharose FF and Sephadex G-100. The anti-complementary activity of Taro-4-I (57.3±4.5%) was similar to that of polysaccharide K (used as the positive control). The molecular weight of Taro-4-I was 200 kDa and it was a polysaccharide composed of 64.4% neutral sugars and 35.6% uronic acid. Taro-4-I activated the complement system through the classical and alternative pathways. The treatment of peritoneal macrophages with Taro-4-I significantly increased the production of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α) in a dose-dependent manner. However, IL-12 production showed maximal activity at 56 µg/ml and subsequently decreased. Splenocytes obtained from mice which were administered Taro-4-I intravenously showed a higher toxicity to Yac-1 cells compared to those obtained from untreated mice in a effector‑to‑target (E/T) ratio-dependent manner. The group treated with 50 µg/ml Taro-4-I showed a significantly increased toxicity to Yac-1 cells compared to the group treated with 500 µg/ml Taro-4-I. The administration of Taro-4-I significantly inhibited the lung metastasis of B16BL6 melanoma cells. However, the group treated with 50 µg/mouse Taro-4-I had a significantly lower number of tumors compared to the group injected with 500 µg/mouse Taro-4-I.

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.

Chemical characteristics and immuno-modulating activities of exo-biopolymers produced by Grifola frondosa during submerged fermentation process

The immuno-modulating activities and chemical characteristics of exo-biopolymer (EX-GF) produced by a submerged mycelial culture of Grifola frondosa were studied. The EX-GF was fractionated into EX-GF-Fr.I, II, and III by Sephadex G-100 gel chromatography. Anti-complementary activity of EX-GF-Fr.III was highest (71.1%) among them, and its activation system occurred through both classical and alternative pathways, where the classical pathway found to be major one. Lysosomal enzyme activity and nitric oxide production ability of macrophage were also found to be mediated by EX-GF-Fr.III. The molecular weight of the EX-GF-Fr.I, II, and III was estimated to be about 163, 40, and 2.8 kDa, respectively. Total sugar and protein contents of the three fractions were 80.3, 61.9 and 89.3%, and 17.3, 35.2, and 10.7%, respectively. The sugar and amino acid compositions of the EX-GF-Fr.I, II, and III were also analyzed in detail.

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.

Activation of early components of complement targets myelin and oligodendrocytes in the aged rhesus monkey brain

The disruption and loss of myelin in the white matter are some of the major changes that occur in the brain with age. In vitro studies suggest a role of the complement system in the catabolic breakdown of myelin membranes. This study presents findings on activation of the early components of complement cascade in the brains of both young and aged rhesus monkeys with evidence of increased complement activation in aged animals. Complement containing oligodendrocytes (CAOs) containing C3d and C4d complement activation products bound to oligodendrocytes and myelinated fibers were found in the brain of normal young and old animals. The CAOs, which also contained activated microglia, were distributed throughout the whole brain and in significantly greater numbers in the aged monkeys. These findings, together with the demonstration of covalent binding of the C3 fragments to myelin, suggest the initiation of the complement cascade by myelin and oligodendrocytes, which are known classical complement activators. Activation of terminal complement components was not demonstrable in the CAOs. Taken together the findings support the concept that activation of early components of complement in the brain may be a normal biological process that involves the metabolism of myelin and oligodendrocytes and up-regulates with age.

C5b-9 complement complex in autoimmune demyelination and multiple sclerosis: dual role in neuroinflammation and neuroprotection

Complement system activation plays an important role in innate and acquired immunity. Activation of complement leads to the formation of C5b-9 terminal complex. While C5b-9 can promote cell lysis, sublytic assembly of C5b-9 on plasma membranes induces cell cycle activation and survival. Multiple sclerosis (MS) and its animal model experimental allergic encephalomyelitis (EAE) are inflammatory demyelinating diseases of the central nervous system (CNS) mediated by activated lymphocytes, macrophages/microglia and the complement system. Complement activation may contribute to the pathogenesis of these diseases through its dual role: the ability of activated terminal complex C5b-9 to promote demyelination and the capacity of sublytic C5b-9 to protect oligodendrocytes (OLG) from apoptosis. By inducing EAE in C5-deficient mice, we showed that complement C5 promotes remyelination and protects oligodendrocytes from apoptotic cell death. These findings indicate that activation of complement C5b-9 plays a pro-inflammatory role in the acute phase of the disease, but may also be neuroprotective during the chronic phase of the disease.

Activation of calpain-1 in myelin and microglia in the white matter of the aged rhesus monkey

Ultrastructural disruption of myelin sheaths and a loss of myelin with age are well-documented phenomena in both the human and rhesus monkey. Age-dependent activation of calpain-1 (EC 3.4.22.52) has been suggested as a plausible mechanism for increased proteolysis in the white matter of the rhesus monkey. The present study documents activation of calpain-1 throughout brain white matter in aged animals, evidenced by immunodetection of the activated enzyme as well as a calpain-derived spectrin fragment in both tissue section and Triton X-100-soluble homogenate of subcortical white matter from the frontal, temporal, and parietal lobes. Separation of myelin fractions from brain stem tissue into intact and floating myelin confirmed previous reports of an age-related increase in activated calpain-1 in the floating fraction. Measurements of calpain-1 activity using a fluorescent substrate revealed an age-related increase in calpain-1 proteolytic activity in the floating myelin fraction consistent with immunodetection of the activated enzyme in this fraction. Double-immunofluorescence demonstrated co-localization of activated calpain-1 with human leukocyte antigen-DR (HLA-DR), a marker for activated microglia, suggesting that these cells represent the major source of the increase in activated calpain-1 in the aging brain. These data solidify the role of calpain-1 in myelin protein metabolism and further implicate activated microglia in the pathology of the aging brain.

Murine complement C4 is not required for experimental autoimmune encephalomyelitis

In vitro studies have demonstrated that myelin and myelin-derived proteins activate both the classical and alternative complement pathways. More recently, studies have shown that mice deficient in factor B, a protein required for activation of the alternative pathway, have attenuated experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. The relative contribution of the classical pathway to the pathogenesis of EAE has remained unexplored. To address this question, we performed EAE using mice deficient in C4 (C4-/-), a protein required for full activation of the classical pathway. We found that deletion of the C4 gene does not significantly change either the time of onset or the severity and tempo of myelin oligodendrocyte-induced EAE compared with controls with a fully intact complement system. We observed similar levels of cellular infiltration (CD11b+ macrophages and CD3+ T cells) and demyelination in the two kinds of mice. Despite this, ribonuclease protection assays demonstrated a two- to fourfold increase in several pro-inflammatory cytokines in C4-/- mice with EAE, including interleukin-beta (IL-1beta), IL-18, tumor necrosis factor-alpha (TNF-alpha), IP-10, and RANTES. These results support the conclusion that the contribution of murine complement to the pathogenesis of demyelinating disease is realized via the alternative pathway.

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.

A hypothesis accounting for the inconsistent benefit of glucocorticoid therapy in closed head trauma

Because of disagreement between clinical studies, the American College of Neurological Surgeons (ACNS) most recent recommendation (1996) is that glucocorticoids should not be used in the treatment of closed head trauma (CHT). The current paper reviews clinical studies of glucocorticoids and CHT in order to examine what factors might have accounted for the inconsistent results leading to the ACNS's recommendation. A careful analysIs of these studies reveals that, contrary to the ACNS's sweeping conclusion, the available data support the use of glucocorticoids for patients with CHT, but only in specific cases. Glucocorticoids may be beneficial in the treatment of CHT uncomplicated by intracranial hemorrhage; in situations where intracranial hemorrhage accompanies CHT, glucocorticoid treatment appears detrimental. The second part of this paper examines possible mechanisms accounting for the differential effectiveness of glucocorticoids in CHT patients with and without intracranial hemorrhage. These mechanisms include vasospasm, free radical damage, blood-borne factors, and glutamate neurotoxicity.

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.

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.

Inhibition of Oligodendrocyte Apoptosis by Sublytic C5b-9 Is Associated with Enhanced Synthesis of Bcl-2 and Mediated by Inhibition of Caspase-3 Activation

We have previously shown that generation of sublytic C5b-9, the membrane attack complex of complement, induces oligodendrocytes to enter cell cycle and reduces apoptotic cell death in vitro. In the present study, the cellular factors involved in apoptosis of oligodendrocyte progenitor cells and oligodendrocytes, and the inhibitory effect of C5b-9 on apoptotic process were investigated. Oligodendrocyte progenitor cells identified by mAb A2B5 that were isolated from neonatal rat brains were differentiated into oligodendrocytes in serum-free defined medium. The differentiation, which occurs simultaneously with apoptotic cell death, was associated with a rapid loss of bcl-2 mRNA and increased expression of caspase-3 mRNA. Activation of caspase-3 in differentiating cells was demonstrated by the generation of 17- and 12-kDa fragments of caspase-3 proenzyme and by cleavage of poly(ADP-ribose) polymerase, a specific caspase-3 substrate. Cell death associated with differentiation was inhibited by the caspase-3 inhibitor DEVD-CHO in a dose-dependent manner. Assembly of sublytic C5b-9 resulted in inhibition of caspase-3 activation. In addition, synthesis of BCL-2 protein in oligodendrocytes was significantly increased by C5b-9. The TNF-α-induced apoptosis of oligodendrocytes was also inhibited by C5b-9. These results indicate that up-regulation of BCL-2 protein and inhibition of caspase-3 activation are potential mechanisms by which C5b-9 increases survival of oligodendrocyte in vitro and possibly in vivo during inflammation and immune-mediated demyelination affecting the CNS.

Multiple sclerosis and central nervous system demyelination

Multiple sclerosis (MS) is characterized by multifocal areas within the CNS of demyelination with relative but not absolute axonal sparing. Initial lesion development appears dependent on T cell infiltration into the CNS; however, lesion expansion may reflect tissue injury induced by additional effector mechanisms derived from cells of the immune system and endogenous CNS cells (glial cells). This relative susceptibility to injury in MS of myelin and its cell of origin, the oligodendrocyte (OL), could reflect either the properties of the effectors or the targets. Effector-determined susceptibility could relate to presence of OL/myelin-restricted T cells or antibody. OLs, at least in vitro, express MHC class I molecules and are susceptible to CD8(+)T cell-mediated cytotoxicity. OL/myelin-specific antibodies are identified in MS lesions and could induce injury via complement- or ADCC-dependent mechanisms. OLs are susceptible to injury-mediated by non-specific cell effectors including NK cells, NK-like T cells (CD56(+)), and gamma/delta T cells via perforin/granzyme-dependent mechanisms. In vitro studies of OL injury mediated via tumor necrosis factor (TNF) and CD95 indicate that differential glial cell susceptibility to injury can depend on cell surface receptor expression and intracellular signaling pathways that are activated. These target-determined susceptibility factors may be amenable to neuroprotective therapies.

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 role of the complement system in traumatic brain injury

A traumatic impact to the brain induces an intracranial inflammatory response, which consequently leads to the development of brain edema and delayed neuronal death. Evidence from experimental, clinical, and in vitro studies highlight an important role for the complement system in contributing to inflammation within the injured brain. The present review summarizes the current understanding of the mechanisms of complement-mediated secondary brain injury after head trauma.

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.

Unique expression of HRF20 (CD59) in human nervous tissue

Damage to autologous tissue by complement is limited by several widely distributed membrane-associated glycoproteins which restrict the action of the complement in homologous species. These include decay accelerating factor (DAF), membrane cofactor protein (MCP) and 20 kDa homologous restriction factor (HRF20,CD59). Using immunohistochemical techniques, we examined the localization of these proteins in the central nervous system (CNS) and peripheral nervous system (PNS) using non-neurological human nervous tissue since some complement components have been demonstrated to be synthesized in the CNS. There was no evidence of parenchymal staining by anti-DAF or anti-MCP antibodies in either type of tissue except for the staining of the endothelium in capillaries. On the other hand, anti-HRF20 antibody clearly stained myelinated axons in the CNS as well as Schwann cells in the PNS. In addition, we detected positive staining by anti-DAF antibody in the PNS of a Paroxysmal nocturnal hemoglobinuria (PNH) patient who is genetically deficient in HRF20.

Complement regulatory protein expression by a human oligodendrocyte cell line: cytokine regulation and comparison with astrocytes

Rat oligodendrocytes spontaneously activate complement (C) and lack the C inhibitor CD59. As a consequence, rat oligodendrocytes are susceptible to lysis by autologous C in vitro. Expression of C inhibitors on human oligodendrocytes in vitro and other human glia has yet to be well characterized. We have previously shown expression at the mRNA level of the membrane inhibitors CD59, decay-accelerating factor (DAF; CD55) and membrane cofactor protein (MCP; CD46) in human astrocytes. We here examine the expression of membrane and secreted C inhibitors by the oligodendrocyte cell line, HOG. HOG cells abundantly expressed CD59, assessed at protein and mRNA level, and expressed DAF and MCP, albeit at a lower level. Expression of all three inhibitors was enhanced by incubation with interferon-gamma or with phorbol ester (PMA). Complement receptor type 1 (CR1; CD35) was neither expressed constitutively nor induced by cytokines. HOG also constitutively secreted C1-inhibitor, S-protein and clusterin. Factor H was secreted only after stimulation with cytokines. C4b binding protein was expressed at a very low level and was detected only at the mRNA level by reverse transcriptase-polymerase chain reaction (RT-PCR). For comparison, astrocyte expression of CD59, DAF, MCP and CR1 was confirmed at the mRNA and protein levels. HOG did not activate C spontaneously, as judged by the lack of deposition of C fragments, and were not lysed by C even after inhibition of CD59 and DAF using specific monoclonal antibodies.

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.

Complement C1q and C3 mRNA expression in the frontal cortex of Alzheimer's patients

The levels and cellular localization of mRNA for complement C1q and C3 were examined by RNA gel blot and nonradioactive in situ hybridization in the frontal cortex of patients with Alzheimer's disease (AD) and age-matched controls. We found that the hybridization signal for C1q mRNA was markedly increased (approx. 3.5-fold) in the frontal cortex of AD patients compared to that in age-matched controls. In contrast to previous reports we also found that the levels of C3 mRNA, although well expressed, did not differ significantly between AD cases and age-matched controls. Nonradioactive in situ hybridization using digoxigenin-labeled ribo-probes revealed that transcripts coding for both C1q and C3 were closely associated with neurons. These results support the hypothesis that complement could play a role in neuronal degeneration which has been observed in the brain of AD patients.

Complement biosynthesis in the central nervous system

Complement is an important effector arm of the human immune response. Binding of proteolytic fragments derived from activation of complement by specific receptors leads to responses as diverse as inflammation, opsonization, and B-cell activation. The importance of characterizing the expression and regulation of complement in the CNS is highlighted by growing evidence that complement plays a significant role in the pathogenesis of a variety of neurological diseases, such as multiple sclerosis and Alzheimer's disease. In vitro studies have demonstrated that astrocytes, the predominant glial cell type in the brain, are capable of expressing or producing a majority of the components of the complement system. Expression of many complement proteins synthesized by astrocytes is regulated by both pro- and anti-inflammatory cytokines, many of which are also produced by several cell types in the CNS. In addition to astrocytes, ependymal cells, endothelial cells, microglia, and neurons have recently been shown to synthesize various complement proteins or express complement receptors on their cell surfaces. Together, these studies demonstrate that several cell types throughout the brain have the potential to express complement and, in many cases, increase expression in response to mediators of the acute phase response. These studies suggest that complement may play a greater role in CNS immune responses than previously thought, and pave the way for better understanding of the dynamics of complement expression and regulation in vivo. Such understanding may lead to therapeutic manipulation of complement host defense functions in a variety of inflammatory and degenerative diseases in the CNS.

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.

Interferon-gamma regulation of C3 gene expression in human astroglioma cells

In this report, we show that the human astroglioma cell line, D54-MG, constitutively expresses C3 mRNA and secretes antigenically detectable C3 protein. The cytokine interferon-gamma (IFN-gamma) enhances C3 mRNA and protein expression by D54-MG cells in a dose- and time-dependent manner. C3 mRNA from both D54-MG cells and primary human adult astrocytes has the same apparent size (5.1-5.2 kb) as C3 mRNA from hepatocyte and monocyte cell lines. Constitutive C3 mRNA levels in D54-MG cells and primary human astrocytes are comparable. Primary rat astrocytes also constitutively express C3 mRNA, which is enhanced upon exposure to IFN-gamma. These data are novel since expression of C3 in other cell types is refractory to IFN-gamma. In the central nervous system (CNS), endogenous complement production by astrocytes, and enhancement by the cytokine IFN-gamma, may contribute to the pathogenesis of inflammatory demyelinating diseases such as multiple sclerosis (MS).

Oligodendrocytes lack glycolipid anchored proteins which protect them against complement lysis. Restoration of resistance to lysis by incorporation of CD59

Rat oligodendrocytes, which activate the classical pathway of complement in the absence of antibody, are highly sensitive in a reactive lysis assay using human C5b6 and EDTA serum. Oligodendrocytes may be relatively deficient in glycolipid-linked complement regulatory protein(s), since digestion with phosphatidylinositol-specific phospholipase C (PI-PLC) failed to increase their sensitivity to serum, whereas complement-insensitive astrocytes, when treated with PI-PLC, became strikingly sensitive. To test the hypothesis that oligodendrocytes lack terminal complement regulatory molecule(s), human erythrocyte CD59, a recently described complement regulatory protein, was purified to homogeneity. The biological activity of the preparation was confirmed by reincorporating the protein into guinea-pig erythrocytes through its glycolipid anchor, which resulted in dose-dependent protection against human C5b6 and EDTA serum. Incorporation of 10(5) molecules of human CD59 into rat oligodendrocytes resulted in good protection against homologous human complement (76%), and significant protection against rat complement homologous to the cell (36%). Protection could be reversed using an antibody to CD59.

Mechanisms of oligodendrocyte interaction with normal human serum--defining the role of complement

The interaction of human serum with oligodendroglia was investigated in vitro using purified cultured neonatal rat oligodendrocytes. Previous evidence for antibody independent classical pathway complement activation was confirmed; the results also showed a deficit in the protection of rat oligodendrocytes from complement attack suggesting a deficiency in the expression of terminal regulatory proteins of the complement cascade. Thus, rat oligodendrocytes are selectively sensitive to normal serum due both to complement activation and impaired protection from terminal complement attack.

The pathogenesis of demyelinating disease: insights from cell biology

Cellular and humoral immune mechanisms have been implicated in the pathogenesis of human and experimental demyelinating diseases of the CNS. How these interact in the complex sequence of events that culminates in phagocytosis of myelin by macrophages has yet to be resolved. The relationship between leakage of the blood-brain barrier and demyelination, the reason why recurrent inflammatory demyelination occurs--seemingly in the absence of an antigen-specific immune response--and the lack of effective remyelination all require explanation if a coherent account of immunologically mediated demyelination is to be achieved. One approach to these problems is to study in vitro the developmental and cellular biology of oligodendrocytes--the glial cells responsible for the synthesis and maintenance of CNS myelin. This provides experimental opportunities not offered by more direct investigation of the intact nervous system, but carries the clear disadvantage that observations made in vitro cannot necessarily be extrapolated to humans.

Oligodendrocytes and oligodendrocyte/type-2 astrocyte progenitor cells of adult rats are specifically susceptible to the lytic effects of complement in absence of antibody

The central nervous system of individuals with multiple sclerosis contains lesions specifically characterized by breakdown of myelin sheaths associated with a general failure of repair of demyelinating damage. The cause of myelin breakdown is unknown. Although immune mechanisms have been implicated in this breakdown, no convincing demonstrations of specific immune reaction against myelin have yet been provided in multiple sclerosis patients. Similarly, the cellular biological mechanisms which underlie the failure of myelin repair are unknown. We have found that (i) oligodendrocytes, the cells that produce myelin sheaths in the central nervous system, and (ii) oligodendrocyte/type-2 astrocyte (O/2A) progenitor cells derived from optic nerves of adult rats bind and activate complement in the absence of antibody in vitro, leading to destruction of these cells. Susceptibility to antibody-independent lysis by complement was a cell-type-specific trait of oligodendrocytes and adult O/2A progenitors and was not shared by perinatal O/2A progenitors, type-2 astrocytes, type-1 astrocytes, meningeal cells, or Schwann cells. We suggest that the susceptibility of oligodendrocytes and adult O/2A progenitor cells to complement-induced lysis, combined with other specific properties of adult O/2A progenitors, are consistent with--and may be a contributing factor--both in the generation of demyelinating lesions in multiple sclerosis and also in the failure of these lesions to be successfully repaired in adult multiple sclerosis patients.

Circumventricular organs in chronic serum sickness: a model for cerebral lupus

The pathogenesis of the CNS manifestations of systemic lupus erythematosus (SLE) has been the subject of considerable investigation. The focus of many of these studies has concerned immune complex deposition within the choroid plexus (CP). Involvement of the other brain fenestrated vascular beds, the small, paraventricular circumventricular organs, has not been ascertained. For this purpose, chronic serum sickness, a good immunopathological experimental model of naturally occurring systemic immunological disorders such as SLE, was induced in Wistar rats by prolonged immunization with bovine serum albumin (BSA). The involvement of circumventricular vascular beds by immune deposits was ascertained immunohistochemically. The choroid plexus was found to be the most intensely involved circumventricular structure. Immune complex deposits were also present, in descending order of frequency, in the area postrema, subfornical organ, and pineal gland.

Immunocytochemical localization of the terminal complement complex in multiple sclerosis

Granular deposits of C9 and the terminal complement complex, measuring 0.3-1.2 microns, have been demonstrated immunocytochemically in association with capillary endothelial cells, predominantly within plaques and adjacent white matter, in tissue obtained at autopsy from 5/7 patients with multiple sclerosis (MS) and one individual with subacute sclerosing panencephalitis but not from 7/7 controls. This finding suggests that the evolution of focal tissue damage in MS may involve complement activation associated with passage of humoral and cellular mediators of the immune system through the blood-brain barrier.

Vesicular removal by oligodendrocytes of membrane attack complexes formed by activated complement

Oligodendrocytes synthesize myelin in the central nervous system and maintain it in lamellar sheaths around axons. Techniques for studying oligodendrocyte development in vitro can be used, indirectly, to investigate the myelin injury that occurs in human and experimental demyelinating disease. Cell-mediated immune mechanisms are necessary but not sufficient to induce myelin damage in vivo; more recently complement has also been implicated in the pathogenesis both of multiple sclerosis and experimental allergic encephalomyelitis. Previously we have demonstrated that antibody-independent complement activation occurs in vitro at the oligodendrocyte surface. Here we show that the ensuing oligodendrocyte injury is reversible, and that recovery involves the release of membrane-attack complex-enriched vesicles from the surface of viable cells. The demonstration of morphologically and immunochemically identical vesicles in the cerebrospinal fluid of patients with multiple sclerosis suggests that reversible complement-mediated injury contributes to myelin damage in vivo.

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

The role of complement in mediating oligodendrocyte and myelin injury has been investigated by studying the effects of normal adult rat serum on syngeneic cultured neonatal glial cells. Rat serum has cytotoxic activity directed against oligodendrocytes but not astrocytes, the potency of which increases with cell maturation. The effects of heat inactivation, decomplemented rat serum, EGTA treatment, removal of any possible anti-myelin antibody by absorption using syngeneic myelin and absence of surface staining for immunoglobulins on serum-treated oligodendrocytes, C9 depletion and reconstitution, and oligodendrocyte staining for surface C9 demonstrate that this cytotoxicity is mediated by complement via antibody independent activation of the classical pathway and is membrane attack complex dependent. These findings significantly extend the previous demonstration of complement activation by extracted myelin, and may have significance for the pathogenesis of demyelinating diseases.

Immune mechanisms in the pathogenesis of demyelinating diseases

The loss of myelin which characterises many human and experimental demyelinating diseases, among them multiple sclerosis, is thought to be immune mediated, but the precise mechanisms responsible remain unknown despite intense research. Normally, myelin in the central nervous system (CNS) is protected from systemic immune responses by the blood brain barrier, which separates nervous tissue from the peripheral circulation. Here we review evidence suggesting that an understanding of the demyelinating disorders may be helped by considering their immune pathogenesis in two stages. The first is damage to the blood brain barrier; this appears to be cell mediated, and allows infiltration into the CNS of other immune effectors. These include complement and also macrophages, which together may mediate the second stage, injury to the myelin/oligodendrocyte complex.

Serum complement activation in central nervous system disease in Sjögren's syndrome

PURPOSE

Central nervous system disease and vasculitis are extraglandular manifestations of Sjögren's syndrome. In our experience, central nervous system disease develops in approximately 70 percent of patients with Sjögren's syndrome and biopsy documented peripheral vasculitis. In order to further investigate the pathogenesis of central nervous system disease and its relationship to peripheral vasculitis in Sjögren's syndrome, we examined sera of patients with Sjögren's syndrome with and without focal central nervous system involvement for evidence of terminal complement pathway activation.

PATIENTS AND METHODS

Patients were classified as having active focal central nervous system involvement only when they had focal neurologic deficits on physical examination, plus at least one abnormal neurodiagnostic test result. Two thirds of these patients also had cognitive or psychiatric dysfunction. Patients were classified as having peripheral vasculitis if they had clinical and histopathologic documentation of vascular inflammation. Serum SC5b-9 was measured by a sensitive enzyme-linked immunoabsorbent assay. Total hemolytic complement assay, measurement of serum C3 and C4 by radial immunodiffusion, and determination of immune complexes were performed.

RESULTS

Fluid-phase terminal complement complexes (SC5b-9) were detected in the sera of 25 of 30 (83 percent) patients with focal central nervous system involvement, but in only seven of 21 (33 percent) patients with Sjögren's syndrome without focal central nervous system disease (p = 0.00084 by Yates' chi-square analysis). Four of these seven patients without focal central nervous system disease, but who had serum SC5b-9, had psychiatric or cognitive dysfunction. SC5b-9 was also detected in sera from 14 of 15 (93 percent) patients with active biopsy-documented peripheral vasculitis in contrast to 18 of 36 (50 percent) patients without clinical evidence of peripheral vasculitis (p = 0.0094). Serum SC5b-9 was a more sensitive indicator of complement activation than circulating immune complex or complement assays.

CONCLUSION

These findings suggest that terminal complement activation may participate in the pathophysiology of both central nervous system and peripheral vasculitis in Sjögren's syndrome. Serum SC5b-9 appears to be a useful diagnostic indicator of vascular inflammation in Sjögren's syndrome and appears to identify those patients at risk for central nervous system complications.

Intrathecal complement activation in neurological diseases evaluated by analysis of the terminal complement complex

The terminal complement complex (TCC) was determined in plasma and cerebrospinal fluid (CSF) from 208 neurological patients. Elevated CSF TCC levels were observed in higher frequencies in patients with infectious diseases (80%), radiculoneuritis (62%), multiple sclerosis (30%), and miscellaneous autoimmune diseases (27%) than in patients with miscellaneous non-inflammatory diseases (2-13%). The plasma level of TCC was significantly increased only in the infectious group. No positive correlation was observed between the plasma and the CSF TCC concentration in the whole patient population nor in subgroups divided according to blood-brain barrier function. Furthermore, the CSF TCC concentration did not correlate with the serum/CSF albumin ratio or with CSF total protein concentration when this was below 1.0 g/l. It is concluded that an elevated TCC concentration in CSF reflects intrathecal complement activation and that quantification of TCC in CSF may be a valuable supplement in the examination of neurological diseases.

Activation of complement by myelin: identification of C1-binding proteins of human myelin from central nervous tissue

Myelin isolated from central nervous tissue activates the classic pathway of complement by directly activating C1. Activation of C1 can proceed to form membrane attack complex, C5b-9, in the myelin. Such an interaction between myelin and complement may be important in diseases involving myelin damage, in view of the role of complement in membrane attack and inflammation. To identify the C1-activating protein, myelin was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot. The blots were incubated with C1 or with whole serum complement, followed by immunostaining for C1 or C3, respectively. A duplicate strip was stained with amido black or anti-myelin antibody to visualize the myelin proteins. The results showed that two major protein bands were capable of activating C1. An approximately 56-58-kilodalton band comigrated with the W2 protein and an approximately 45-47-kilodalton band migrated along with, but slightly behind, the W1 Wolfgram doublet.

Complement potentiates the degradation of myelin proteins by plasmin: implications for a mechanism of inflammatory demyelination

A previous finding, that the basic protein in lyophilized bovine myelin was degraded by macrophage-conditioned media in the presence of plasminogen, suggested that the macrophage-secreted plasminogen activator, along with plasminogen, might have a role in destruction of myelin during inflammatory demyelination. To approximate more closely the conditions expected in vivo, plasmin, or macrophage supernatants plus plasminogen, were incubated with freshly homogenized bovine white matter or freshly isolated myelin, as distinguished from lyophilized myelin. Under these conditions basic protein was not degraded. Phospholipase or lysolecithin potentiated the degradation of basic protein in fresh bovine myelin by plasmin; however, the cultured macrophages did not secrete significant amounts of phospholipase and plasminogen activator simultaneously into the culture media after activation with any of several different agents. Recently myelin was shown to activate complement. After preincubation of fresh myelin with guinea pig serum, as a source of complement, the basic and proteolipid proteins were vulnerable to plasmin or to macrophage-conditioned media plus plasminogen. C3-depleted and C4-deficient sera were not effective, suggesting that these complement components were required for the serum effect. Hypothetically, then, degradation of myelin proteins in the CNS could be initiated by plasminogen activator, secreted by infiltrating macrophages, plus complement and plasminogen, which could enter the CNS through lesions in the blood-brain barrier.

Purification and characterization of complement activating-acidic polysaccharide from the root of Lithospermum euchromum Royle

An extraordinary potent anti-complementary substance was isolated from the root of Lithospermum euchromum Royle (Japanese name: Nan-shikon) which activates the complement system in vitro, and the active principle was shown to be acidic polysaccharide (LR-polysaccharide IIa). LR-polysaccharide IIa was purified by chromatographies on DEAE-Sepharose, Sephadex G-100, concanavalin A-Sepharose, Ricinus communis agglutinin conjugated Sepharose, Sepharose CL-6B and Sepharose CL-2B. LR-polysaccharide IIa was found to be composed of rhamnose, fucose, arabinose, xylose, mannose, galactose and glucose in the molar ratios of 2.0:2.5:3.4:2.8:5.6:9.6:14.4. The polysaccharide also contained 15% of galacturonic acid and 3.8% of protein. The methylation analysis of the polysaccharide showed that rhamnose, arabinofuranose, xylose, glucose and galactose are present as a part of the nonreducing terminal residues. The main chain and side chains are composed of ----3Glc1----,----3Gal1----,----6Man1----,----4Gal1, [corrected] and the branching points consist of (formula; see erratum) These results indicated that LR-polysaccharide IIa has a highly complicated structure. A marked consumption of C4 was observed after the incubation of the serum with LR-polysaccharide IIa in the presence of the Ca++ ion. The anti-complementary activity of LR-polysaccharide IIa was reduced partially in the absence of the Ca++ ion. After the incubation of the serum with LR-polysaccharide IIa in the absence of Ca++ ion, a cleavage of C3 in the serum was found to have occurred through immunoelectrophoresis as well as from the consumption of the complement when rabbit erythrocytes were used in the assay system. These results indicate that the mode of complement activation by LR-polysaccharide IIa is via both the alternative and classical pathways. Complement titer also decreased in guinea pigs upon i.p. injection of LR-polysaccharide IIa.

Complement in the pathophysiology and diagnosis of human diseases

Complement is a humoral effector system composed of 21 plasma proteins that was identified initially because of its cytolytic effects. In addition to cytolysis, complement has a number of different functions related to inflammatory and other host defense processes. The description of the reaction mechanism includes: (1) activation of the classical pathway through recognition of IgG and IgM antibodies by C1q, (2) activation of the alternative pathway which is usually achieved without participation of immunoglobulins, (3) generation of proteolytic enzymes composed of heteropolymers that cleave certain precursor proteins, (4) formation of the membrane attack complex (MAC), and (5) participation of control mechanisms. Methodologies for studying protein concentration and functional activities of complement components include not only the classical hemolytic techniques but also the extremely sensitive new radioimmunoassays and enzyme immunoassays for measuring the products of complement activation that are generated in vivo. Examples of genetically controlled complement deficiencies have been published for most complement components. The symptomatology of some of these patients serves to emphasize the protective role of complement. Acquired deficiencies are significant not only as laboratory aids in diagnosis and to evaluate the course of certain diseases, but also to indicate possible pathogenic disease mechanisms. Recently, it has been recognized that the complement proteins with genes located in the HLA region are polymorphic. Certain variants of proteins C2, C4, and factor B occur with higher frequencies in certain diseases than in the general population, which appears to be of great practical importance in laboratory medicine.

The development of complement activating ability as an age related factor in murine brains

We recently reported on the ability of the myelin fraction of the murine brain to activate the complement system through the classical pathway, which might be important in the induction of secondary inflammation in various pathological conditions where brain tissue has been exposed to the complement. The present study was undertaken to investigate the relationship between the appearance of complement activity in the mouse brain and the synthesis of myelin in ICR mice up to ninety days of age. Here, we show that anti-complementary activity in the murine brain is closely related to murine brain weight and that its activity seems to be dependent on the amount of myelin in the murine brain. Myelin was isolated from brains of equal weight taken from both two-day old and ninety-day-old mice, and we found that ninety-day-old myelin consumed a much greater amount of complement (C) than two-day-old myelin. However, for equal concentrations of myelin, almost an equal amount of C was consumed by the myelin of the two-day-old mice and by that of the ninety-day-old mice. It was suggested that the difference of anti-complementary activity was caused by the myelin contents of the murine brains, but the possibility of maturation of myelin was not excluded. The mechanism involved in the anticomplementary activity of the myelin was found to be related to the consumption of complement, mainly via the classical pathway but also less activity via the alternative pathway.