Expression of C1q, a subcomponent of the rat complement system, is dramatically enhanced in brains of rats with either Borna disease or experimental allergic encephalomyelitis

Interaction Between the Complement System and Infectious Agents - A Potential Mechanistic Link to Neurodegeneration and Dementia

As part of the innate immune system, complement plays a critical role in the elimination of pathogens and mobilization of cellular immune responses. In the central nervous system (CNS), many complement proteins are locally produced and regulate nervous system development and physiological processes such as neural plasticity. However, aberrant complement activation has been implicated in neurodegeneration, including Alzheimer’s disease. There is a growing list of pathogens that have been shown to interact with the complement system in the brain but the short- and long-term consequences of infection-induced complement activation for neuronal functioning are largely elusive. Available evidence suggests that the infection-induced complement activation could be protective or harmful, depending on the context. Here we summarize how various infectious agents, including bacteria (e.g., Streptococcus spp.), viruses (e.g., HIV and measles virus), fungi (e.g., Candida spp.), parasites (e.g., Toxoplasma gondii and Plasmodium spp.), and prion proteins activate and manipulate the complement system in the CNS. We also discuss the potential mechanisms by which the interaction between the infectious agents and the complement system can play a role in neurodegeneration and dementia.

Role of intracellular complement activation in kidney fibrosis

Increased expression of complement C1r, C1s and C3 in kidney cells plays an important role in the pathogenesis of kidney fibrosis. Our studies suggest that activation of complement in kidney cells with increased generation of C3 and its fragments occurs by activation of classical and alternative pathways. Single nuclei RNA sequencing studies in kidney tissue from unilateral ureteral obstruction mice show that increased synthesis of complement C3 and C5 occurs primarily in renal tubular epithelial cells (proximal and distal), while increased expression of complement receptors C3ar1 and C5ar1 occurs in interstitial cells including immune cells like monocytes/macrophages suggesting compartmentalization of complement components during kidney injury. Although global deletion of C3 and macrophage ablation prevent inflammation and reduced kidney tissue scarring, the development of mice with cell-specific deletion of complement components and their regulators could bring further insights into the mechanisms by which intracellular complement activation leads to fibrosis and progressive kidney disease. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

The role of picornavirus infection in epileptogenesis

Picornaviridae are a family of small positive-strand RNA viruses, and transmitted via the respiratory or fecal-oral route. The neurotropic picornaviruses can induce acute or late recurrent seizures following central nervous system infection, by infecting the peripheral nerve, crossing the blood-brain barrier and migrating in the Trojan-horse method. Theiler’s murine encephalomyelitis virus (TMEV), as a member of Picornaviridae family, can cause encephalitis, leading to chronic spontaneous seizures. TMEV-infected C57BL/6 mice have been used as an animal model for exploring the mechanism of epileptogenesis and assessing new antiepileptic drugs. Astrogliosis, neuronal death and microglial recruitment have been detected in the hippocampus following the picornaviruse-induced encephalitis. The macrophages, monocytes, neutrophils, as well as IL-6 and TNF-α released by them, play an important role in the epileptogenesis. In this review, we summarize the clinical characteristics of picornavirus infection, and the immunopathology involved in the TMEV-induced epilepsy.

Transient increase of microglial C1q expression in the circumventricular organs of adult mouse during LPS-induced inflammation

The circumventricular organs (CVOs) are the brain regions that lack the blood-brain barrier and allow free entry of blood-derived molecules, offering specialized niche to initiate rapid and early neuroinflammatory responses in the brain. Complement component 1q (C1q) is shown to be the first recognition component of the complement pathway and has a crucial function in the brain under pathological conditions. In the present study, we found that C1q expression in CX3CR1-positive microglia was increased in the CVOs and their neighbouring brain regions of adult mice at 1 day after a single administration of 1 mg/kg lipopolysaccharide (LPS), whereas it returned to control levels at 3 days after LPS stimulation. C1q expression was also seen to localize at synapsin-positive presynaptic axonal terminals in various brain regions. Thus, the present study demonstrates a transient upregulation of microglial C1q expression in the CVOs and their adjacent brain regions, indicating that a transient upregulation of C1q is possibly concerned with physiological responses at early phase of brain inflammation. SIGNIFICANCE OF THE STUDY: The circumventricular organs (CVOs) are specialized brain regions that lack the blood-brain barrier (BBB) and initiate neuroinflammatory responses in the brains. The present study showed that the expression of complement protein C1q was highly increased in microglia of the CVOs and their adjacent brain regions. Moreover, C1q expression was observed to localize specifically at presynaptic axonal terminals in the CVOs and their neighbouring brain regions. Thus, the present study indicates that C1q is possibly correlated with physiological responses at early phase of brain inflammation.

Significance of Complement System in Ischemic Stroke: A Comprehensive Review

The complement system is an essential part of innate immunity, typically conferring protection via eliminating pathogens and accumulating debris. However, the defensive function of the complement system can exacerbate immune, inflammatory, and degenerative responses in various pathological conditions. Cumulative evidence indicates that the complement system plays a critical role in the pathogenesis of ischemic brain injury, as the depletion of certain complement components or the inhibition of complement activation could reduce ischemic brain injury. Although multiple candidates modulating or inhibiting complement activation show massive potential for the treatment of ischemic stroke, the clinical availability of complement inhibitors remains limited. The complement system is also involved in neural plasticity and neurogenesis during cerebral ischemia. Thus, unexpected side effects could be induced if the systemic complement system is inhibited. In this review, we highlighted the recent concepts and discoveries of the roles of different kinds of complement components, such as C3a, C5a, and their receptors, in both normal brain physiology and the pathophysiology of brain ischemia. In addition, we comprehensively reviewed the current development of complement-targeted therapy for ischemic stroke and discussed the challenges of bringing these therapies into the clinic. The design of future experiments was also discussed to better characterize the role of complement in both tissue injury and recovery after cerebral ischemia. More studies are needed to elucidate the molecular and cellular mechanisms of how complement components exert their functions in different stages of ischemic stroke to optimize the intervention of targeting the complement system.

Efficacy and mechanisms underlying the effects of allogeneic umbilical cord mesenchymal stem cell transplantation on acute radiation injury in tree shrews

Umbilical cord mesenchymal stem cells (UC-MSCs) exert strong immunomodulatory effects and can repair organs. However, their roles in radiation injury remain unclear. We show that in tree shrews with acute radiation injury, injected UC-MSCs significantly improved survival rates, reduced lung inflammation and apoptosis, prevented pulmonary fibrotic processes, recovered hematopoiesis, and increased blood counts. A protein microarray analysis showed that serum levels of the anti-inflammatory cytokines IL-10 and IL-13 and the growth factors BMP-5, BMP-7, HGF, insulin, NT-4, VEGFR3, and SCF were significantly higher, while those of the inflammatory cytokines IL-2, TIMP-2, TNF-α, IFN-γ, IL-1ra, and IL-8 and the fibrosis-related factors PDGF-BB, PDGF-AA, TGF-β1, IGFBP-2, and IGFBP-4 were significantly lower in UC-MSC-injected animals. A transcriptome analysis of PBMCs showed that the mRNA expression of C1q was upregulated, while that of HLA-DP was downregulated after UC-MSC injection. These results confirm the immunohistochemistry results. eGFP-labeled UC-MSCs were traced in vivo and found in the heart, liver, spleen, lungs, kidneys, thymus, small intestine and bone marrow. Our findings suggest that UC-MSC transplantation may be a novel therapeutic approach for treating acute radiation injury.

Avian Ganglioneuritis in Clinical Practice

Avian ganglioneuritis (AG) comprises one of the most intricate pathologies in avian medicine and is researched worldwide. Avian bornavirus (ABV) has been shown to be a causative agent of proventricular dilatation disease in birds. The avian Bornaviridae represent a genetically diverse group of viruses that are widely distributed in captive and wild populations around the world. ABV and other infective agents are implicated as a cause of the autoimmune pathology that leads to AG, similar to human Guillain Barrè syndrome. Management of affected birds is beneficial and currently centered at reducing neurologic inflammation, managing secondary complications, and providing nutritional support.

Cell specificity dictates similarities in gene expression in multiple sclerosis, Parkinson's disease, and Alzheimer's disease

Drug repurposing is an efficient approach in new treatment development since it leverages previous work from one disease to another. While multiple sclerosis (MS), Parkinson's disease (PD), and Alzheimer's disease (AD) are all neurodegenerative diseases of the central nervous system (CNS) and differ in many clinical and pathological aspects, it is possible that they may share some mechanistic features. We hypothesized that focusing on gene expression in a CNS cell type specific manner might uncover similarities between diseases that could be missed using whole tissue gene expression analyses. We found similarities and differences in gene expression in these three distinct diseases, depending upon cell type. Microglia genes were increased in all three diseases, and gene expression levels were correlated strongly among these three neurodegenerative diseases. In astrocytes and endothelia, upregulation and correlations were observed only between MS and PD, but not AD. Neuronal genes were down-regulated in all three diseases, but correlations of changes of individual genes between diseases were not strong. Oligodendrocyte showed gene expression changes that were not shared among the three diseases. Together these data suggest that treatments targeting microglia are most amenable to drug repurposing in MS, PD, and AD, while treatments targeting other CNS cells must be tailored to each disease.

Complement Components Are Expressed by Infiltrating Macrophages/Activated Microglia Early Following Viral Infection

The individual innate immune components, interleukin-6 and complement component C3, play a role in the development of acute seizures in the Theiler's murine encephalomyelitis virus-induced seizure model. We examined the mRNA expression of various other complement components, cytokines, chemokines, and major histocompatibility complex antigens both within brain and in isolated ramified microglial and infiltrating macrophage/activated microglial cell populations over a time course covering the first 3 days postinfection. We found that complement component C3 showed the greatest increase in expression in brain of all of the complement components assayed and its level of expression was higher in infiltrating macrophages/activated microglia than in ramified microglial cells.

CCAAT/enhancer binding protein β directly regulates the expression of the complement component 3 gene in neural cells: implications for the pro-inflammatory effects of this transcription factor

Background

The CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor, which was first identified as a regulator of differentiation and inflammatory processes mainly in adipose tissue and liver; however, its function in the brain was largely unknown for many years. Previous studies from our laboratory indicated that C/EBPβ is implicated in inflammatory process and brain injury, since mice lacking this gene were less susceptible to kainic acid-induced injury.

Methods

We first performed cDNA microarrays analysis using hippocampal RNA isolated from C/EBPβ^+/+ and C/EBPβ^−/− mice. Immunocytochemical and immunohistochemical studies were done to evaluate C/EBPβ and C3 levels. Transient transfection experiments were made to analyze transcriptional regulation of C3 by C/EBPβ. To knockdown C/EBPβ and C3 expression, mouse astrocytes were infected with lentiviral particles expressing an shRNA specific for C/EBPβ or an siRNA specific for C3.

Results

Among the genes displaying significant changes in expression was complement component 3 (C3), which showed a dramatic decrease in mRNA content in the hippocampus of C/EBPβ^−/− mice. C3 is the central component of the complement and is implicated in different brain disorders. In this work we have found that C/EBPβ regulates C3 levels in rodents glial in vitro and in the rat Substantia nigra pars compacta (SNpc) in vivo following an inflammatory insult. Analysis of the mouse C3 promoter showed that it is directly regulated by C/EBPβ through a C/EBPβ consensus site located at position −616/-599 of the gene. In addition, we show that depletion of C/EBPβ by a specific shRNA results in a significant decrease in the levels of C3 together with a reduction in the increased levels of pro-inflammatory agents elicited by lipopolysaccharide treatment.

Conclusions

Altogether, these results indicate that C3 is a downstream target of C/EBPβ, and it could be a mediator of the pro-inflammatory effects of this transcription factor in neural cells.

Complement modulation of T cell immune responses during homeostasis and disease

The complement system is an ancient and critical effector mechanism of the innate immune system as it senses, kills, and clears infectious and/or dangerous particles and alerts the immune system to the presence of the infection and/or danger. Interestingly, an increasing number of reports have demonstrated a clear role for complement in the adaptive immune system as well. Of note, a number of recent studies have identified previously unknown roles for complement proteins, receptors, and regulators in T cell function. Here, we will review recent data demonstrating the influence of complement proteins C1q, C3b/iC3b, C3a (and C3aR), and C5a (and C5aR) and complement regulators DAF (CD55) and CD46 (MCP) on T cell function during homeostasis and disease. Although new concepts are beginning to emerge in the field of complement regulation of T cell function, future experiments should focus on whether complement is interacting directly with the T cell or is having an indirect effect on T cell function via APCs, the cytokine milieu, or downstream complement activation products. Importantly, the identification of the pivotal molecular pathways in the human systems will be beneficial in the translation of concepts derived from model systems to therapeutic targeting for treatment of human disorders.

Minocycline effects on the cerebrospinal fluid proteome of experimental autoimmune encephalomyelitis rats

To identify response biomarkers for pharmaceutical treatment of multiple sclerosis, we induced experimental autoimmune encephalomyelitis (EAE) in rats and treated symptomatic animals with minocycline. Cerebrospinal fluid (CSF) samples were collected 14 days after EAE induction at the peak of neurological symptoms, and proteomics analysis was performed using nano-LC-Orbitrap mass spectrometry. Additionally, the minocycline concentration in CSF was determined using quantitative matrix-assisted laser desorption/ionization-triple-quadrupole tandem mass spectrometry (MALDI-MS/MS) in the selected reaction monitoring (SRM) mode. Fifty percent of the minocycline-treated EAE animals did not show neurological symptoms on day 14 ("responders"), while the other half displayed neurological symptoms ("nonresponders"), indicating that minocycline delayed disease onset and attenuated disease severity in some, but not all, animals. Neither CSF nor plasma minocycline concentrations correlated with the onset of symptoms or disease severity. Analysis of the proteomics data resulted in a list of 20 differentially abundant proteins between the untreated animals and the responder group of animals. Two of these proteins, complement C3 and carboxypeptidase B2, were validated by quantitative LC-MS/MS in the SRM mode. Differences in the CSF proteome between untreated EAE animals and minocycline-treated responders were similar to the differences between minocycline-treated responders and nonresponders (70% overlap). Six proteins that remained unchanged in the minocycline-treated animals but were elevated in untreated EAE animals may be related to the mechanism of action of minocycline.

Complement protein C1q directs macrophage polarization and limits inflammasome activity during the uptake of apoptotic cells

Deficiency in C1q, the recognition component of the classical complement cascade and a pattern recognition receptor involved in apoptotic cell clearance, leads to lupus-like autoimmune diseases characterized by auto-antibodies to self proteins and aberrant innate immune cell activation likely due to impaired clearance of apoptotic cells. In this study, we developed an autologous system using primary human lymphocytes and human monocyte-derived macrophages (HMDMs) to characterize the effect of C1q on macrophage gene expression profiles during the uptake of apoptotic cells. C1q bound to autologous apoptotic lymphocytes modulated expression of genes associated with JAK/STAT signaling, chemotaxis, immunoregulation, and NLRP3 inflammasome activation in LPS-stimulated HMDMs. Specifically, C1q sequentially induced type I IFNs, IL-27, and IL-10 in LPS-stimulated HMDMs and IL-27 in HMDMs when incubated with apoptotic lymphocyte conditioned media. Coincubation with C1q tails prevented the induction of type I IFNs and IL-27 in a dose-dependent manner, and neutralization of type I IFNs partially prevented IL-27 induction by C1q. Finally, C1q decreased procaspase-1 cleavage and caspase-1-dependent cleavage of IL-1β suggesting a potent inhibitory effect of C1q on inflammasome activation. These results identify specific molecular pathways induced by C1q to suppress macrophage inflammation and provide potential therapeutic targets to control macrophage polarization and thus inflammation and autoimmunity.

Neurotropic viral infections leading to epilepsy: focus on Theiler's murine encephalomyelitis virus

Neurotropic viruses cause viral encephalitis and are associated with the development of seizures/epilepsy. The first infection-driven animal model for epilepsy, the Theiler's murine encephalomyelitis virus-induced seizure model is described herein. Intracerebral infection of C57BL/6 mice with Theiler's murine encephalomyelitis virus induces acute seizures from which the animals recover. However, once the virus is cleared, a significant portion of the animals that experienced acute seizures later develop epilepsy. Components of the innate immune response to viral infection, including IL-6 and complement component 3, have been implicated in the development of acute seizures. Multiple mechanisms, including neuronal cell destruction and cytokine activation, play a role in the development of acute seizures. Future studies targeting the innate immune response will lead to new therapies for seizures/epilepsy.

Complement protein C1q-mediated neuroprotection is correlated with regulation of neuronal gene and microRNA expression

Activation of the complement cascade, a powerful effector mechanism of the innate immune system, is associated with neuroinflammation but also with elimination of inappropriate synapses during development. Synthesis of C1q, a recognition component of the complement system, occurs in brain during ischemia/reperfusion and Alzheimer's disease, suggesting that C1q may be a response to injury. In vitro, C1q, in the absence of other complement proteins, improves neuronal viability and neurite outgrowth and prevents β-amyloid-induced neuronal death, suggesting that C1q may have a direct neuroprotective role. Here, investigating the molecular basis for this neuroprotection in vitro, addition of C1q to rat primary cortical neurons significantly upregulated expression of genes associated with cholesterol metabolism, such as cholesterol-25-hydroxylase and insulin induced gene 2, and transiently decreased cholesterol levels in neurons, known to facilitate neurite outgrowth. In addition, the expression of syntaxin-3 and its functional association with synaptosomal-associated protein 25 was increased. C1q also increased the nuclear translocation of cAMP response element-binding protein and CCAAT/enhancer-binding protein-δ (C/EBP-δ), two transcription factors involved in nerve growth factor (NGF) expression and downregulated specific microRNAs, including let-7c that is predicted to target (and thus inhibit) NGF and neurotrophin-3 (NT-3) mRNA. Accordingly, C1q increased expression of NGF and NT-3, and small interfering RNA inhibition of C/EBP-δ, NGF, or NT-3 expression prevented the C1q-dependent neurite outgrowth. No such neuroprotective effect is seen in the presence of C3a or C5a. Finally, the induced neuronal gene expression required conformationally intact C1q. These results show that C1q can directly promote neuronal survival, thereby demonstrating new interactions between immune proteins and neuronal cells that may facilitate neuroprotection.

Possible involvement of complement factor C1q in the clearance of extracellular neuromelanin from the substantia nigra in Parkinson disease

Activation of the complement system promotes the removal of pathogens and tissue damage products from the brain and may also be involved in neuronal cell death in neurodegenerative diseases. Here, we analyzed the expression of C1q, the initial recognition subcomponent of the classic complement cascade, in the substantia nigra pars compacta (SNc) in Parkinson disease (PD) and control cases using immunohistochemistry and in situ hybridization. Microglia were determined to be the only cells that expressed C1q in the SNc and other brain areas. In the SNc of PD cases, there was increased deposition of extracellular neuromelanin in the parenchyma, resulting from degeneration of dopaminergic neurons. Neuromelanin granules and blebs of degenerated neurons seemed to be opsonized by C1q and phagocytosed by C1q-positive microglia and macrophages in the parenchyma and in the perivascular spaces. Neuromelanin-laden C1q-positive cells were also attached to the luminal surfaces of blood vessels in the SNc in PD. Thus, we present evidence suggesting that microglia are capable of phagocytosing and clearing cellular debris of degenerating neurons from the SNc through a C1q-mediated pathway in PD.

Role for complement in the development of seizures following acute viral infection

Complement, part of the innate immune system, acts to remove pathogens and unwanted host material. Complement is known to function in all tissues, including the central nervous system (CNS). In this study, we demonstrated the importance of the complement system within the CNS in the development of behavioral seizures following Theiler's murine encephalomyelitis virus (TMEV) infection. C57BL/6 mice, deficient in complement component C3, developed significantly fewer behavioral seizures following TMEV infection, whereas mice depleted of complement component C3 in the periphery through treatment with cobra venom factor had a seizure rate comparable to that of control mice. These studies indicate that C3 participates in the induction of acute seizures during viral encephalitis.

C1q, the recognition subcomponent of the classical pathway of complement, drives microglial activation

Microglia, central nervous system (CNS) resident phagocytic cells, persistently police the integrity of CNS tissue and respond to any kind of damage or pathophysiological changes. These cells sense and rapidly respond to danger and inflammatory signals by changing their cell morphology; by release of cytokines, chemokines, or nitric oxide; and by changing their MHC expression profile. We have shown previously that microglial biosynthesis of the complement subcomponent C1q may serve as a reliable marker of microglial activation ranging from undetectable levels of C1q biosynthesis in resting microglia to abundant C1q expression in activated, nonramified microglia. In this study, we demonstrate that cultured microglial cells respond to extrinsic C1q with a marked intracellular Ca(2+) increase. A shift toward proinflammatory microglial activation is indicated by the release of interleukin-6, tumor necrosis factor-alpha, and nitric oxide and the oxidative burst in rat primary microglial cells, an activation and differentiation process similar to the proinflammatory response of microglia to exposure to lipopolysaccharide. Our findings indicate 1) that extrinsic plasma C1q is involved in the initiation of microglial activation in the course of CNS diseases with blood-brain barrier impairment and 2) that C1q synthesized and released by activated microglia is likely to contribute in an autocrine/paracrine way to maintain and balance microglial activation in the diseased CNS tissue.

Complement component C1q inhibits beta-amyloid- and serum amyloid P-induced neurotoxicity via caspase- and calpain-independent mechanisms

Alzheimer's disease is a neurodegenerative disorder characterized by neuronal loss, beta-amyloid (Abeta) plaques, and neurofibrillary tangles. Complement protein C1q has been found associated with fibrillar Abeta deposits, however the exact contributions of C1q to Alzheimer's disease is still unknown. There is evidence that C1q, as an initiator of the inflammatory complement cascade, may accelerate disease progression. However, neuronal C1q synthesis is induced after injury/infection suggesting that it may be a beneficial response to injury. In this study, we report that C1q enhances the viability of neurons in culture and protects neurons against Abeta- and serum amyloid P (SAP)-induced neurotoxicity. Investigation of potential signaling pathways indicates that caspase and calpain are activated by Abeta, but C1q had no effect on either of these pathways. Interestingly, SAP did not induce caspase and calpain activation, suggesting that C1q neuroprotection is in distinct from caspase and calpain pathways. In contrast to Abeta- and SAP-induced neurotoxicity, neurotoxicity induced by etoposide or FCCP was unaffected by the addition of C1q, indicating pathway selectivity for C1q neuroprotection. These data support a neuroprotective role for C1q which should be further investigated to uncover mechanisms which may be therapeutically targeted to slow neurodegeneration via direct inhibition of neuronal loss.

The Double-Edged Flower: Roles of Complement Protein C1q in Neurodegenerative Diseases

A role for the complement cascade in AD neuropathology was hypothesized over a decade ago, and the results of a significant number of in vitro studies are consistent with the involvement of this pathway in AD pathogenesis (reviewed in). Since C1q is colocalized with thioflavine-positive plaques and the C5b-9 complement membrane attack complex is detected in AD brain at autopsy, it is reasonable to hypothesize that complement activation has a role in the manifestation of AD either by its lytic capacity or as a trigger of glial infiltration and initiation of potentially damaging inflammation. The observed diminished glial activation and reduced loss of neuronal integrity in a murine model overexpressing mutant human APP but lacking the ability to activate the classical complement cascade provide the first direct evidence for a detrimental role of C1q, and presumably activation of the classical complement pathway in an animal model of AD. Research is now focused on generating mouse models that more closely mimic the human disease, so that the role of complement activation and inflammation on the behavioral/learning and memory dysfunction that occurs in this disease can be assessed. In addition, candidate therapies such as targeted inhibition of complement activation will need to be tested in these animal models as a step toward treatment of humans with the disease. However, it is important that the potential for a protective effect of C1q early on in disease progression should not be overlooked. Rather, strategies that enhance or mimic the protective effects of C1q as well as strategies that inhibit the detrimental processes should be fully investigated.

Generation of inhibitory NFkappaB complexes and phosphorylated cAMP response element-binding protein correlates with the anti-inflammatory activity of complement protein C1q in human monocytes

The interaction of C1q with specific cells of the immune system induces activities, such as enhancement of phagocytosis in monocytes and stimulation of superoxide production in neutrophils. In contrast to some other monocyte activators, C1q itself does not induce pro-inflammatory cytokine production, but rather inhibits the lipopolysaccharide (LPS)-stimulated induction of certain pro-inflammatory cytokines and induces expression of interleukin-10. To investigate the molecular mechanism by which C1q exerts this effect on gene expression, the influence of C1q on the activation of transcription factors of the NFkappaB family and cAMP response element-binding protein (CREB) was assessed. C1q treatment increased kappaB binding activity in freshly isolated human monocytes in a time-dependent fashion as assessed by electrophoretic mobility shift assays. In antibody supershift experiments, anti-p50 antibody supershifted the C1q-induced NFkappaB complex, whereas anti-p65 antibody had little effect, suggesting that C1q induced the translocation of NFkappaB p50p50 homodimers. This is in contrast to the dominant induction of p65 containing complexes in parallel monocyte cultures stimulated with LPS. C1q treatment also induced cAMP response element (CRE)-binding activity as demonstrated by electrophoretic mobility shift assay, increased phosphorylation of CREB, and induction of CRE driven gene expression. In contrast, CREB activation was not detected in LPS-treated monocytes. These results suggest that C1q may modulate the cytokine profile expressed in response to inflammatory stimuli (e.g. LPS), by triggering inhibitory and/or competing signals. Because C1q and other defense collagens have been shown to enhance clearance of apoptotic cells, this regulatory pathway may be beneficial in avoiding autoimmunity and/or resolving inflammation.

The role of astrocytes and complement system in neural plasticity

In neurotrauma, brain ischemia or neurodegenerative diseases, astrocytes become reactive (which is known as reactive gliosis) and this is accompanied by an altered expression of many genes. Two cellular hallmarks of reactive gliosis are hypertrophy of astrocyte processes and the upregulation of the part of the cytoskeleton known as intermediate filaments, which are composed of nestin, vimentin, and GFAP. Our aim has been to better understand the function of reactive astrocytes in CNS diseases. Using mice deficient for astrocyte intermediate filaments (GFAP(-/-)Vim(-/-)), we were able to attenuate reactive gliosis and slow down the healing process after neurotrauma. We demonstrated the key role of reactive astrocytes in neurotrauma-at an early stage after neurotrauma, reactive astrocytes have a neuroprotective effect; at a later stage, they facilitate the formation of posttraumatic glial scars and inhibit CNS regeneration, specifically, they seem to compromise neural graft survival and integration, reduce the extent of synaptic regeneration, inhibit neurogenesis in the old age, and inhibit regeneration of severed CNS axons. We propose that reactive astrocytes are the future target for the therapeutic strategies promoting regeneration and plasticity in the brain and spinal cord in various disease conditions. Through its involvement in inflammation, opsonization, and cytolysis, complement protects against infectious agents. Although most of the complement proteins are synthesized in CNS, the role of the complement system in the normal or ischemic CNS remains unclear. Complement activiation in the CNS has been generally considered as contributing to tissue damage. However, growing body of evidence suggests that complement may be a physiological neuroprotective mechanism as well as it may participate in maintenance and repair of the adult brain.

Viral-induced inflammation is accompanied by beta-amyloid plaque reduction in brains of amyloid precursor protein transgenic Tg2576 mice

Amyloid plaques, one of the neuropathological hallmarks of Alzheimer's disease, and their main constituent, the amyloid beta-peptide (Abeta), are triggers of the activation of innate inflammatory mechanisms involving the activation of microglia. To dissect the effects of a non-Abeta-specific microglial activation on the Abeta metabolism, we employed a viral infection-based model. Transgenic mice expressing a mutated form of the human amyloid precursor protein (Tg2576) were used. In preceding experiments, 2-week-old transgenic mice and non-transgenic littermates were infected intracerebrally with the neurotropic Borna disease virus and investigated at 2, 4 and 14 weeks post-infection. The Borna disease virus-inoculated mice showed a persisting, subclinical infection of cortical and limbic brain areas characterized by slight T-cell infiltrates, expression of cytokines and a massive microglial activation in the hippocampus and neocortex. Viral-induced effects reached their peak at 4 weeks post-infection. In 14-month-old Tg2576 mice, characterized by the deposition of diffuse and dense-core amyloid plaques in cortical brain regions, Borna disease virus-induced microglial activation in the vicinity of Abeta deposits was used to investigate the influence of a local inflammatory response on these deposits. At 4 weeks post-infection, histometric analyses employing Abeta immunohistochemistry revealed a decrease of the cortical and hippocampal Abeta-immunopositive area. This overall decrease was accompanied by a decrease of parenchymal thioflavin-S-positive amyloid deposits and an increase of such deposits in the walls of cerebral vessels, which indicates that the elicitation of a non-Abeta-specific microglial activation may contribute to a reduction of Abeta in the brain parenchyma.

Early hypothalamic response to age-dependent gene expression by calorie restriction

Molecular events linking the initial detection of calorie restriction (CR) to changes in gene expression throughout the organism that ultimately retard aging in CR animals are unknown. This study measured changes in gene expression induced by CR and by aging in the hypothalamus, which likely plays a central role in the initial perception of and response to CR. Hypothalamic expression profiling was done in young (4-6 months) ad libitum fed (AL), young CR (2.5-4.5 months of CR), and old (26-28 months) AL male C57BL/6 mice. CR altered the expression of 137 genes and aging altered 1222. Only 8 age-related genes were oppositely regulated by CR. To test whether reduced plasma glucose is a signal in altering hypothalamic gene expression, we examined GLUT4 transgenic mice (C57BL/6 background; 4-6 months), which have reduced plasma glucose similar to that of CR mice. Twenty-seven genes differed between transgenic and non-transgenic mice; nine of these were only altered by CR. The decreased plasma glucose had a limited role in CR mediated hypothalamic gene expression.

Complement proteins C1q and MBL are pattern recognition molecules that signal immediate and long-term protective immune functions

C1q and mannose binding lectin, members of the "defense collagen" family, are pattern recognition molecules that can trigger rapid enhanced phagocytosis resulting in efficient containment of pathogens or clearance of cellular debris, apoptotic cells and immune complexes. In addition, interaction of C1q and mannose binding lectin with the phagocyte alters subsequent phagocyte cytokine synthesis, and thus may have important implications in directing acute inflammation as well as long-term protective immunity. The importance of the role of defense collagens in phagocytosis of apoptotic cells is highlighted by studies in vivo of mice deficient in C1q, pulmonary surfactant D and mannose binding lectin in which there is delayed clearance of apoptotic cells. Indeed, deficiency of C1q is a risk factor for the development of autoimmunity in both humans and mice, consistent with the hypothesis that inefficient clearance of apoptotic cells results in release of autoantigens and contributes to the pathology associated with autoimmune diseases such as systemic lupus erythematosus. Further understanding of the importance of C1q and mannose binding lectin in the clearance of apoptotic cells and regulation of cytokine synthesis and identification of the receptors implicated in mediating these processes should provide novel targets for therapeutic intervention in the control and manipulation of the immune response in terms of both host defense against infectious disease and tissue repair and remodeling.

Attenuated rabies virus activates, while pathogenic rabies virus evades, the host innate immune responses in the central nervous system

Rabies virus (RV) induces encephalomyelitis in humans and animals. However, the pathogenic mechanism of rabies is not fully understood. To investigate the host responses to RV infection, we examined and compared the pathology, particularly the inflammatory responses, and the gene expression profiles in the brains of mice infected with wild-type (wt) virus silver-haired bat RV (SHBRV) or laboratory-adapted virus B2C, using a mouse genomic array (Affymetrix). Extensive inflammatory responses were observed in animals infected with the attenuated RV, but little or no inflammatory responses were found in mice infected with wt RV. Furthermore, attenuated RV induced the expression of the genes involved in the innate immune and antiviral responses, especially those related to the alpha/beta interferon (IFN-alpha/beta) signaling pathways and inflammatory chemokines. For the IFN-alpha/beta signaling pathways, many of the interferon regulatory genes, such as the signal transduction activation transducers and interferon regulatory factors, as well as the effector genes, for example, 2'-5'-oligoadenylate synthetase and myxovirus proteins, are highly induced in mice infected with attenuated RV. However, many of these genes were not up-regulated in mice infected with wt SHBRV. The data obtained by microarray analysis were confirmed by real-time PCR. Together, these data suggest that attenuated RV activates, while pathogenic RV evades, the host innate immune and antiviral responses.

Attenuated rabies virus activates, while pathogenic rabies virus evades, the host innate immune responses in the central nervous system

Rabies virus (RV) induces encephalomyelitis in humans and animals. However, the pathogenic mechanism of rabies is not fully understood. To investigate the host responses to RV infection, we examined and compared the pathology, particularly the inflammatory responses, and the gene expression profiles in the brains of mice infected with wild-type (wt) virus silver-haired bat RV (SHBRV) or laboratory-adapted virus B2C, using a mouse genomic array (Affymetrix). Extensive inflammatory responses were observed in animals infected with the attenuated RV, but little or no inflammatory responses were found in mice infected with wt RV. Furthermore, attenuated RV induced the expression of the genes involved in the innate immune and antiviral responses, especially those related to the alpha/beta interferon (IFN-alpha/beta) signaling pathways and inflammatory chemokines. For the IFN-alpha/beta signaling pathways, many of the interferon regulatory genes, such as the signal transduction activation transducers and interferon regulatory factors, as well as the effector genes, for example, 2'-5'-oligoadenylate synthetase and myxovirus proteins, are highly induced in mice infected with attenuated RV. However, many of these genes were not up-regulated in mice infected with wt SHBRV. The data obtained by microarray analysis were confirmed by real-time PCR. Together, these data suggest that attenuated RV activates, while pathogenic RV evades, the host innate immune and antiviral responses.

Expression of allograft inflammatory factor-1 and haeme oxygenase-1 in brains of rats infected with the neurotropic Borna disease virus

Experimental infection of Lewis rats with Borna disease virus (BDV) causes an immune-mediated nonpurulent meningoencephalitis. Viral persistence in the central nervous system is accompanied by mononuclear infiltrates, activated monocytic/microglial cells and reactive astrocytes. The immune-mediated process was further characterized by expression analysis of allograft inflammatory factor-1 (AIF-1), a novel marker of monocyte/microglial activation and of glial fibrillary acid protein (GFAP) between day 3 and day 50 post infection (p.i.). Potential neuroprotective effects of these cells were studied by the induction of haeme oxygenase-1 (HO-1), a defensive molecule against oxidative stress in various brain insults. In BDV-infected rat brains, mononuclear infiltrates and AIF-1 expression increased up to day 28 p.i. During early time points p.i., AIF-1 expression was mainly found in inflammatory lesions and adjacent brain parenchyma. Already 24 days p.i., a widespread upregulation of AIF-1 was observed which declined only moderately beyond day 28 p.i. HO-1 induction was maximal between days 18 and 28 p.i. Increased amounts of GFAP-positive astrocytes were present beyond 24 days p.i. Viral antigen expression increased simultaneously to the inflammatory reaction and persisted up to 50 days p.i. Widespread upregulation of AIF-1 indicates an early, long-lasting microglial activation, which might be involved in the immunesurveillance of the immune-mediated inflammatory events. The early peak of HO-1 most likely represents a neuroprotective, anti-inflammatory response by invading monocytes, microglial cells and astrocytes during the formation of encephalitic lesions and acute viral replication.

Genetic study of the myelin oligodendrocyte glycoprotein (MOG) gene in schizophrenia

Schizophrenia (SCZ) is a neuropsychiatric disorder that affects approximately 1% of the general population. The human leukocyte antigen (HLA) system has been implicated in several genetic studies of SCZ. The myelin oligodendrocyte glycoprotein (MOG) gene, which is located close to the HLA region, is considered a candidate for SCZ due to its association with white matter abnormalities and its importance in mediating the complement cascade. Four polymorphisms in the MOG gene (CA)n (TAAA)n, and two intronic polymorphisms, C1334T and C10991T, were investigated for the possibility of association with SCZ using 111 SCZ proband and their families. We examined the transmission of the alleles of each of these polymorphisms with the transmission disequilibrium test. We did not observe significant evidence for biased transmission of alleles at the (CA)n (chi2=2.430, 6 df, P=0.876) (TAAA)n (chi2=3.550, 5 df, P=0.616), C1334T (chi2=0.040, 1 df, P=0.841) and C10991T (chi2=0.154, 1 df, P=0.695) polymorphisms. Overall haplotype analysis using the TRANSMIT program was also not significant (chi2=7.954, 9 df, P=0.539). Furthermore, our results comparing mean age at onset in the genotype groups using the Kruskal-Wallis Test were not significant. Our case-control analyses (182 cases age-, sex- and ethnicity-matched with healthy controls) and combined z-score [(CA)n: z-score=-1.126, P=0.130; (TAAA)n: z-score=-0.233, P=0.408; C1334T: z-score=0.703, P=0.241; C10991T: z-score=0.551, P=0.291] were also not significant. Although our data are negative, the intriguing hypothesis for MOG in SCZ may warrant further investigation of this gene.

Absence of C1q leads to less neuropathology in transgenic mouse models of Alzheimer's disease

C1q, the recognition component of the classical complement activation pathway, is a multifunctional protein known to be expressed in brain of Alzheimer's disease (AD) patients. To experimentally address the role of C1q in AD, a mouse model lacking C1q (APPQ-/-) was generated by crossing Tg2576 animals (APP) with C1q-deficient mice. The pathology of APPQ-/- was compared with that of APP mice and B6SJL controls at 3-16 months of age by immunohistochemistry and Western blot analysis. At younger ages (3-6 months), when no plaque pathology was present, no significant differences were seen in any of the neuronal or glial markers tested. At older ages (9-16 months), the APP and APPQ-/- mice developed comparable total amyloid and fibrillar beta-amyloid in frontal cortex and hippocampus; however, the level of activated glia surrounding the plaques was significantly lower in the APPQ-/- mice at 12 and 16 months. In addition, although Tg2576 mice showed a progressive decrease in synaptophysin and MAP2 in the CA3 area of hippocampus compared with control B6SJL at 9, 12, and 16 months, the APPQ-/- mice had significantly less of a decrease in these markers at 12 and 16 months. In a second murine model for AD containing transgenes for both APP and mutant presenilin 1 (APP/PS1), a similar reduction of pathology was seen in the APPPS1Q-/- mice. These data suggest that at ages when the fibrillar plaque pathology is present, C1q exerts a detrimental effect on neuronal integrity, most likely through the activation of the classical complement cascade and the enhancement of inflammation.

Brain microglia and blood-derived macrophages: molecular profiles and functional roles in multiple sclerosis and animal models of autoimmune demyelinating disease

Microglia and macrophages, one a brain-resident, the other a mostly hematogenous cell type, represent two related cell types involved in the brain pathology in multiple sclerosis and its autoimmune animal model, the experimental allergic encephalomyelitis. Together, they perform a variety of different functions: they are the primary sensors of brain pathology, they are rapidly recruited to sites of infection, trauma or autoimmune inflammation in experimental allergic encephalomyelitis and multiple sclerosis and they are competent presenters of antigen and interact with T cells recruited to the inflamed CNS. They also synthesise a variety of molecules, such as cytokines (TNF, interleukins), chemokines, accessory molecules (B7, CD40), complement, cell adhesion glycoproteins (integrins, selectins), reactive oxygen radicals and neurotrophins, that could exert a damaging or a protective effect on adjacent axons, myelin and oligodendrocytes. The current review will give a detailed summary on their cellular response, describe the different classes of molecules expressed and their attribution to the blood derived or brain-resident macrophages and then discuss how these molecules contribute to the neuropathology. Recent advances using chimaeric and genetically modified mice have been particularly telling about the specific, overlapping and nonoverlapping roles of macrophages and microglia in the demyelinating disease. Interestingly, they point to a crucial role of hematogenous macrophages in initiating inflammation and myelin removal, and that of microglia in checking excessive response and in the induction and maintenance of remission.

Decay-Accelerating Factor (CD55) Is Expressed by Neurons in Response to Chronic but Not Acute Autoimmune Central Nervous System Inflammation Associated with Complement Activation

There is compelling evidence that a unique innate immune response in the CNS plays a critical role in host defense and clearance of toxic cell debris. Although complement has been implicated in neuronal impairment, axonal loss, and demyelination, some preliminary evidence suggests that the initial insult consequently activates surrounding cells to signal neuroprotective activities. Using two different models of experimental autoimmune encephalomyelitis, we herein demonstrate selective C1q complement activation on neuron cell bodies and axons. Interestingly, in brains with chronic but not acute experimental autoimmune encephalomyelitis, C3b opsonization of neuronal cell bodies and axons was consistently associated with robust neuronal expression of one of the most effective complement regulators, decay-accelerating factor (CD55). In contrast, levels of other complement inhibitors, complement receptor 1 (CD35), membrane cofactor protein (CD46), and CD59 were largely unaffected on neurons and reactive glial cells in both conditions. In vitro, we found that proinflammatory stimuli (cytokines and sublytic doses of complement) failed to up-regulate CD55 expression on cultured IMR32 neuronal cells. Interestingly, overexpression of GPI-anchored CD55 on IMR32 was capable of modulating raft-associated protein kinase activities without affecting MAPK activities and neuronal apoptosis. Critically, ectopic expression of decay-accelerating factor conferred strong protection of neurons against complement attack (opsonization and lysis). We conclude that increased CD55 expression by neurons may represent a key protective signaling mechanism mobilized by brain cells to withstand complement activation and to survive within an inflammatory site.

Restoration of C1q levels by bone marrow transplantation attenuates autoimmune disease associated with C1q deficiency in mice

C1q deficiency in both humans and mice is strongly associated with autoimmunity. We have previously shown that bone marrow transplantation (BMT) restored C1q levels in C1q-deficient (C1qa(-/-)) mice. Here, we studied the effect of BMT on autoimmunity in C1qa(-/-) mice. Following irradiation, young C1qa(-/-) or wild-type MRL/Mp mice received bone marrow cells (BMC) from strain-matched wild-type or C1qa(-/-) animals. C1q levels increased rapidly when C1qa(-/-) mice received BMC from wild-type mice. Conversely, they decreased slowly in wild-type mice transplanted with C1qa(-/-) BMC. C1qa(-/-) animals transplanted with C1qa(-/-) BMC demonstrated accelerated disease when compared with wild-type mice given wild-type BMC. In contrast, a significant delay in the development of autoantibodies and glomerulonephritis was observed in C1qa(-/-) mice reconstituted with wild-type BMC, and the impaired clearance of apoptotic cells, previously described in C1qa(-/-) mice, was rectified. Moreover, the autoimmune disease was accelerated in wild-type mice given C1qa(-/-) BMC compared to animals transplanted with wild-type cells. These results provide supporting evidence that BMT may be a therapeutic option in the treatment of autoimmunity associated with human C1q deficiency.

Myelin oligodendrocyte glycoprotein (MOG) gene is associated with obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a severe neuropsychiatric disorder with a strong genetic component, and may involve autoimmune processes. Support for this latter hypothesis comes from the identification of a subgroup of children, described by the term pediatric autoimmune neuropsychiatric disorder associated with streptococcal infections (PANDAS), with onset of OCD symptoms following streptococcal infections. Genes involved in immune response therefore represent possible candidate genes for OCD, including the myelin oligodendrocyte glycoprotein (MOG) gene, which plays an important role in mediating the complement cascade in the immune system. Four polymorphisms in the MOG gene, a dinucleotide CA repeat (MOG2), a tetranucleotide TAAA repeat (MOG4), and 2 intronic single nucleotide polymorphisms, C1334T and C10991T, were investigated for the possibility of association with OCD using 160 nuclear families with an OCD proband. We examined the transmission of alleles of these four polymorphisms with the transmission disequilibrium test (TDT). A biased transmission of the 459-bp allele (allele 2: chi2 = 5.255, P = 0.022) of MOG4 was detected, while MOG2, C1334T, and C10991T showed no statistically significant bias in the transmission of alleles. The transmission of the C1334T.MOG2.C10991T.MOG4 haplotype 1.13.2.2 (chi2 = 6.426, P = 0.011) was also significant. Quantitative analysis using the family-based association test (FBAT) was significant for MOG4 in total Yale-Brown Obsessive-Compulsive Scale severity score (allele 2: z = 2.334, P = 0.020). Further investigations combining genetic, pathological, and pharmacological strategies, are warranted.

Microglial activation and increased synthesis of complement component C1q precedes blood-brain barrier dysfunction in rats

A reliable way to visualise the state of microglial activation is to monitor the microglial gene expression profile. Microglia are the only CNS resident cells that synthesise C1q, the recognition sub-component of the classical complement pathway, in vivo. C1q biosynthesis in resting ramified microglia is often low, but it increases dramatically in activated microglia. In this study, the expression of C1q was used to monitor microglial activation at all stages of 3-chloropropanediol-induced neurotoxicity, a new model of blood-brain barrier (BBB) breakdown. In rats, 3-chloropropanediol produces very focused lesions in the brain, characterised by early astrocyte swelling and loss, followed by neuronal death and barrier dysfunction. Using in situ hybridisation, immunohistochemistry, and real-time RT-PCR, we found that increased C1q biosynthesis and microglial activation precede BBB dysfunction by at least 18 and peak 48 h after injection of 3-chloropropanediol, which coincides with the onset of active haemorrhage. Microglial activation is biphasic; an early phase of global activation is followed by a later phase in which microglial activation becomes increasingly focused in the lesions. During the early phase, expression of the pro-inflammatory mediators interleukin-1beta (IL1beta), tumour necrosis factor alpha (TNFalpha) and early growth response-1 (Egr-1) increased in parallel with C1q, but was restricted to the lesions. Expression of C1q (but not IL1beta, TNFalpha or Egr-1) remains high after BBB function is restored, and is accompanied by late up-regulation of the C1q-associated serine proteases, C1r and C1s, suggesting that microglial biosynthesis of the activation complex of the classical pathway may support the removal of cell debris by activation of complement.

Complement C1q expression induced by Aβ in rat hippocampal organotypic slice cultures

Amyloid beta peptide (Abeta) is a major component of senile plaques, one of the principle pathological features in Alzheimer's disease (AD) brains. Fibrillar Abeta has been shown to bind C1 via C1q, the recognition component of the classical complement pathway, resulting in the activation of the complement pathway, thereby initiating an inflammatory cascade in the brain. C1q has also been shown to enhance phagocytic activities of microglia, which could benefit in clearance of apoptotic cells or cellular debris. To begin to define the role of C1q in tissue injury mediated by Abeta, we assessed the appearance of C1q in hippocampal slice cultures treated with freshly solubilized or fibrillar Abeta 1-42. Here we demonstrate a dose- and time-dependent uptake of exogenously applied Abeta by pyramidal neurons in organotypic slice cultures from rat hippocampus. Importantly, when slices were immunostained with antibody against rat C1q, a distinct reactivity for C1q in cells within the neuronal cell layer of cornu ammonis (CA) of hippocampus, primarily the CA1/CA2, was observed in the Abeta-treated slices. No such immunoreactivity was detected in untreated cultures or upon addition of control peptides. ELISA assays also showed an increase in C1q in tissue extracts from slices of the treated group. Similarly, the mRNA level of C1q in slices was increased within 24 h after Abeta treatment. These data demonstrate that upon exposure to Abeta, C1q is expressed in neurons in this organotypic system. The induction of C1q may be an early, perhaps beneficial, tissue or cellular response to injury triggered by particular pathogenic stimuli.

Neuronal localization of C1q in preclinical Alzheimer's disease

Complement has been postulated to contribute to inflammatory reactions associated with the neuropathology of Alzheimer's disease (AD). C1q, an initial component of the complement cascade, is associated with neuritic plaques and with neurons in the hippocampus of AD brain. Here, we report the presence of C1q in a cognitively intact subject, previously identified as preclinical AD. We compared in detail brain tissue of this preclinical case with a genetically related late-onset AD case. In the AD brain, C1q was typically associated with fibrillar Abeta plaques in frontal cortex and with plaques and neurons in the hippocampus. In the preclinical subject, C1q was abundantly present but it was cell-associated only, being primarily colocalized with neurons in both frontal cortex and hippocampus. However, no predominant cortical neuronal C1q localization was found in other preclinical cases or in Down's cases of different ages. Thus, it is possible that this neuronal-associated C1q reflects an early, but transient, response to injury that may modulate the progression of neurological dysfunction in AD.

Spinal cord involvement in the nonhuman primate model of Lyme disease

Lyme borreliosis is a multisystemic disease caused by infection with various genospecies of the spirochete Borrelia burgdorferi. The organs most often affected are the skin, joints, the heart, and the central and peripheral nervous systems. Multiple neurological complications can occur, including aseptic meningitis, encephalopathy, facial nerve palsy, radiculitis, myelitis, and peripheral neuropathy. To investigate spinal cord involvement in the nonhuman primate (NHP) model of Lyme borreliosis, we inoculated 25 adult Macaca mulatta with B. burgdorferi sensu strictu strains N40 by needle (N=9) or by tick (N=4) or 297 by needle (N=2), or with B. burgdorferi genospecies garinii strains Pbi (N=4), 793 (N=2), or Pli (N=4) by needle. Immunosuppression either transiently (TISP) or permanently (IS) was used to facilitate establishment of infection. Tissues and fluids were collected at necropsy 7-24 weeks later. Hematoxylin and eosin staining was used to study inflammation, and immunohistochemistry and digital image analysis to measure inflammation and localize spirochetes. The spirochetal load and C1q expression were measured by TaqMan RT-PCR. The results showed meningoradiculitis developed in only one of the 25 NHP's examined, TISP NHP 321 inoculated with B. garinii strain Pbi. Inflammation was localized to nerve roots, dorsal root ganglia, and leptomeninges but rarely to the spinal cord parenchyma itself. T cells and plasma cells were the predominant inflammatory cells. Significantly increased amounts of IgG, IgM, and C1q were found in inflamed spinal cord. Taqman RT-PCR found spirochetes in the spinal cord only in IS-NHP's, mostly in nerve roots and ganglia rather than in the cord parenchyma. C1q mRNA expression was significantly increased in inflamed spinal cord. This is the first comprehensive study of spinal cord involvement in Lyme borreliosis.

CNS gene expression pattern associated with spontaneous experimental autoimmune encephalomyelitis

Transgenic mice with T-cell receptor (TCR) specific for myelin basic protein (MBP)-Ac1-11 peptide and homozygous for the RAG-1 mutation (T/R- mice) spontaneously develop acute progressive experimental autoimmune encephalomyelitis (Sp-EAE) mediated by CD4+ T cells. Microarray analysis of spinal cord tissue obtained from symptomatic versus non-symptomatic T/R- mice revealed strongly upregulated transcripts for genes involved in antigen presentation and processing, signal transduction, transcription regulation, metabolism, development, cell cycle, and many other processes involved in the induction of clinical and pathological signs of Sp-EAE. Several highly expressed genes were related directly to inflammation, including cytokines/receptors, chemokines/receptors, acute phase, complement molecules, and others. Many CNS-specific genes were also upregulated in sick mice. Abundance of message for the Tg TCR BV8S2 gene as well as several monocyte/macrophage-associated genes would suggest that both components play a crucial role in the pathogenesis of Sp-EAE. The profile of transcriptional changes found during the development of Sp-EAE provides the first description of the encephalitogenic process in the absence of purposeful immunization with myelin peptides and immune-enhancing adjuvants. This unique approach is the first to implicate molecules and pathways that contribute naturally to onset of paralysis and demyelination, and thus may provide unique insights and novel treatment strategies for human diseases such as multiple sclerosis.

Activation of complement in the central nervous system: roles in neurodegeneration and neuroprotection

The complement system is an essential effector of the humoral and cellular immunity involved in cytolysis and immune/inflammatory responses. Complement participates in host defense against pathogens by triggering the formation of the membrane attack complex. Complement opsonins (C1q, C3b, and iC3b) interact with surface complement receptors to promote phagocytosis, whereas complement anaphylatoxins C3a and C5a initiate local inflammatory responses that ultimately contribute to the protection and healing of the host. However, activation of complement to an inappropriate extent has been proposed to promote tissue injury. There is now compelling evidence that complement activation in the brain is a double-edged sword in that it can exert beneficial or detrimental effects depending on the pathophysiological context. This review focuses on the roles of the complement system in the pathogenesis of acute brain injury (cerebral ischemia and trauma) and chronic neurodegeneration (Alzheimer's disease). Because many effects of the complement appear to promote neuronal survival and tissue remodeling, directing activation of the complement system in the brain may provide a better therapeutic rationale than inhibiting it.

Differential expression of the murine mannose-binding lectins A and C in lymphoid and nonlymphoid organs and tissues

Mannose-binding lectin (MBL), a member of the collectin family, binds to carbohydrate structures on the surfaces of micro-organisms and may serve as a recognition molecule of the lectin pathway of complement activation. In rodents two forms, MBL-A and MBL-C, were described and shown to be products of two related, but uncoupled, genes. The liver is the main source of MBL biosynthesis. For rat MBL-A, expression has also been described in the kidney. Here we report that the two forms of murine MBL are differentially expressed in a number of nonhepatic tissues. Real-time RT-PCR revealed that the liver is the major site of expression for both MBL genes. Lower copy numbers were found in kidney, brain, spleen, and muscle. In testis, only the MBL-A gene is expressed, whereas MBL-C is exclusively expressed in small intestine. Using in situ hybridization and immunohistochemistry, we demonstrate that both MBLs are synthesized by hepatocytes and show MBL expression in cells of the monocyte/macrophage lineage. In the kidney MBL-A, but not MBL-C, was found to be synthesized. Vice versa, only MBL-C biosynthesis was detected in endothelial cells of the small intestine. The latter finding may support the view that MBL-C, as part of the innate immune system, may be a counterpart of secretory IgA of the acquired immune system in preventing, for example, microbial invasion and colonization. Our findings demonstrate that MBL-A and MBL-C are differentially expressed, implying distinct biological roles for both recognition molecules of the murine lectin pathway of complement.

Innate immunity in viral encephalitis: role of C5

The complement system is a critical component of both the innate and acquired immune systems. It is important in host defense against viruses, bacteria, and fungi for opsonization and for lysis of pathogens. However, activated complement can also cause tissue damage. There is compelling evidence that complement factors are presented in the central nervous system (CNS). Complement activation (by any of the three pathways: classical, alternate, and lectin) can lead to inflammation and tissue damage, while at the same time may also restrict certain pathogens in the CNS. C5a is formed by proteolytic cleavage C5. C5a is considered the most potent proinflammatory mediator, often called an anaphylotoxin. In this communication, we examine the roles of C5 (C5a) in vesicular stomatitis virus (VSV)-induced encephalitis. We found that C5a is produced during VSV infection, but C5-deficient mice had similar pathology as their controls. We concluded that C5 is not a critical factor in mediating the host response during VSV encephalitis.

In vivo biosynthesis of endogenous and of human C1 inhibitor in transgenic mice: tissue distribution and colocalization of their expression

We have produced transgenic mice expressing human C1 inhibitor mRNA and protein under the control of the human promoter and regulatory elements. The transgene was generated using a minigene construct in which most of the human C1 inhibitor gene (C1NH) was replaced by C1 inhibitor cDNA. The construct retained the promoter region extending 1.18 kb upstream of the transcription start site, introns 1 and 2 as well as a stretch of 2.5 kb downstream of the polyadenylation site, and therefore carried all known elements involved in transcriptional regulation of the C1NH gene. Mice with high serum levels of human C1 inhibitor, resulting from multiple tandem integrations of the C1 inhibitor transgene, were selected. Immunohistochemistry in combination with in situ hybridization was applied to localize the sites of C1 inhibitor biosynthesis and to demonstrate its local production in brain, spleen, liver, heart, kidney, and lung. The distribution of human C1 inhibitor-expressing cells was qualitatively indistinguishable from that of its mouse counterpart, but expression levels of the transgene were significantly higher. In the spleen, production of C1 inhibitor was colocalized with that of a specific marker for white pulp follicular dendritic cells. This study demonstrates a stringently regulated expression of both the endogenous and the transgenic human C1 inhibitor gene and reveals local biosynthesis of C1 inhibitor at multiple sites in which the components of the macromolecular C1 complex are also produced.