Neuroinflammation induced by intracerebroventricular injection of microbial neuraminidase

Inducible miR-1224 silences cerebrovascular Serpine1 and restores blood flow to the stroke-affected site of the brain

The α-tocotrienol (TCT) form of natural vitamin E is more potent than the better known α-tocopherol against stroke. Angiographic studies of canine stroke have revealed beneficial cerebrovascular effects of TCT. This work seeks to understand the molecular basis of such effect. In mice, TCT supplementation improved perfusion at the stroke-affected site by inducing miR-1224. miRNA profiling of a laser-capture-microdissected stroke-affected brain site identified miR-1224 as the only vascular miR induced. Lentiviral knockdown of miR-1224 significantly blunted the otherwise beneficial effects of TCT on stroke outcomes. Studies on primary brain microvascular endothelial cells revealed direct angiogenic properties of miR-1224. In mice not treated with TCT, advance stereotaxic delivery of an miR-1224 mimic to the stroke site markedly improved stroke outcomes. Mechanistic studies identified Serpine1 as a target of miR-1224. Downregulation of Serpine1 augmented the angiogenic response of the miR-1224 mimic in the brain endothelial cells. The inhibition of Serpine1, by dietary TCT and pharmacologically, increased cerebrovascular blood flow at the stroke-affected site and protected against stroke. This work assigns Serpine1, otherwise known to be of critical significance in stroke, a cerebrovascular function that worsens stroke outcomes. miR-1224-dependent inhibition of Serpine1 can be achieved by dietary TCT as well as by the small-molecule inhibitor TM5441.

Microbial neuraminidase induces TLR4-dependent long-term immune priming in the brain

Innate immune memory explains the plasticity of immune responses after repeated immune stimulation, leading to either enhanced or suppressed immune responses. This process has been extensively reported in peripheral immune cells and also, although modestly, in the brain. Here we explored two relevant aspects of brain immune priming: its persistence over time and its dependence on TLR receptors. For this purpose, we used an experimental paradigm consisting in applying two inflammatory stimuli three months apart. Wild type, toll-like receptor (TLR) 4 and TLR2 mutant strains were used. The priming stimulus was the intracerebroventricular injection of neuraminidase (an enzyme that is present in various pathogens able to provoke brain infections), which triggers an acute inflammatory process in the brain. The second stimulus was the intraperitoneal injection of lipopolysaccharide (a TLR4 ligand) or Pam3CSK4 (a TLR2 ligand). One day after the second inflammatory challenge the immune response in the brain was examined. In wild type mice, microglial and astroglial density, as well as the expression of 4 out of 5 pro-inflammatory genes studied (TNFα, IL1β, Gal-3, and NLRP3), were increased in mice that received the double stimulus compared to those exposed only to the second one, which were initially injected with saline instead of neuraminidase. Such enhanced response suggests immune training in the brain, which lasts at least 3 months. On the other hand, TLR2 mutants under the same experimental design displayed an enhanced immune response quite similar to that of wild type mice. However, in TLR4 mutant mice the response after the second immune challenge was largely dampened, indicating the pivotal role of this receptor in the establishment of immune priming. Our results demonstrate that neuraminidase-induced inflammation primes an enhanced immune response in the brain to a subsequent immune challenge, immune training that endures and that is largely dependent on TLR4 receptor.

Anxiety-like behavior and microglial activation in the amygdala after acute neuroinflammation induced by microbial neuraminidase

Short-term behavioral alterations are associated with infection and aid the recovery from sickness. However, concerns have raised that sustained behavioral disturbances after acute neuroinflammation could relate to neurological diseases in the long run. We aimed to explore medium- and long-term behavioral disturbances after acute neuroinflammation in rats, using a model based on the intracerebroventricular administration of the enzyme neuraminidase (NA), which is part of some pathogenic bacteria and viruses. Neurological and behavioral assessments were performed 2 and 10 weeks after the injection of NA, and neuroinflammation was evaluated by gene expression and histology. No alterations were observed regarding basic neurological functions or locomotor capacity in NA-injected rats. However, they showed a reduction in unsupported rearing, and increased grooming and freezing behaviors, which indicate anxiety-like behavior. A principal component analysis including a larger set of parameters further supported such anxiety-like behavior. The anxiety profile was observed 2 weeks after NA-injection, but not after 10 weeks. Concomitantly, the amygdala presented increased number of microglial cells showing a morphologic bias towards an activated state. A similar but subtler tendency was observed in hypothalamic microglia located in the paraventricular nucleus. Also, in the hypothalamus the pattern recognition receptor toll-like receptor 4 (TLR4) was slightly overexpressed 2 weeks after NA injection. These results demonstrate that NA-induced neuroinflammation provokes anxiety-like behavior in the medium term, which disappears with time. Concurrent microgliosis in the amygdala could explain such behavior. Further experiments should aim to explore subtle but long-lasting alterations observed 10 weeks after NA injection, both in amygdala and hypothalamus, as well as mild behavioral changes.

Long-term priming of hypothalamic microglia is associated with energy balance disturbances under diet-induced obesity

Exposure of microglia to an inflammatory environment may lead to their priming and exacerbated response to future inflammatory stimuli. Here we aimed to explore hypothalamic microglia priming and its consequences on energy balance regulation. A model of intracerebroventricular administration of neuraminidase (NA, which is present in various pathogens such as influenza virus) was used to induce acute neuroinflammation. Evidences of primed microglia were observed 3 months after NA injection, namely (1) a heightened response of microglia located in the hypothalamic arcuate nucleus after an in vivo inflammatory challenge (high fat diet [HFD] feeding for 10 days), and (2) an enhanced response of microglia isolated from NA‐treated mice and challenged in vitro to LPS. On the other hand, the consequences of a previous NA‐induced neuroinflammation were further evaluated in an alternative inflammatory and hypercaloric scenario, such as the obesity generated by continued HDF feeding. Compared with sham‐injected mice, NA‐treated mice showed increased food intake and, surprisingly, reduced body weight. Besides, NA‐treated mice had enhanced microgliosis (evidenced by increased number and reactive morphology of microglia) and a reduced population of POMC neurons in the basal hypothalamus. Thus, a single acute neuroinflammatory event may elicit a sustained state of priming in microglial cells, and in particular those located in the hypothalamus, with consequences in hypothalamic cytoarchitecture and its regulatory function upon nutritional challenges.

Cellular distribution of C-C motif chemokine ligand 2 like immunoreactivities in frontal cortex and corpus callosum of normal and lipopolysaccharide treated animal

BACKGROUND

C-C motif chemokine ligand 2 (CCL2) is reported to be involved in the pathogenesis of various neurological and/or psychiatric diseases. Tissue or cellular expression of CCL2, in normal or pathological condition, may play an essential role in recruiting monocytes or macrophages into targeted organs, and be involved in a certain pathogenic mechanism. However, few studies focused on tissue and cellular distribution of the CCL2 peptide in brain grey and white matters (GM, WM), and the changes of the GM and WM cellular CCL2 level in septic or endotoxic encephalopathy was not explored. Hence, the CCL2 cellular distribution in the front brain cortex and the corpus callosum (CC) was investigated in the present work by using immunofluorescent staining.

RESULTS

(1) CCL2 like immunoreactivity (CCL2-ir) in the CC is evidently higher than the cortex. When the measurement includes ependymal layer attached to the CC, CCL2-ir intensity is significantly higher than cortex. (2) Structures in perivascular areas, most of them are GFAP positive, contribute major CCL2-ir positive profiles in both GM and WM, but apparently more in the CC, where they are bilaterally distributed in the lateral CC between the cingulate cortex and ventricles. (3) The neuron-like CCL2-ir positive cells in cortex are significantly more than in the CC, and that number is significantly increased in the cortex following systemic lipopolysaccharide (LPS), but not in the CC. (4) In addition to CCL2-ir positive perivascular rings, more CCL2-ir filled cashew shape elements are observed, probably inside of microvasculature, especially in the CC following systemic LPS. (5) Few macrophage/microglia marker-Iba-1 and CCL2-ir co-labeled structures especially the soma is found in normal cortex and CC; the co-localizations are significantly augmented following systemic LPS, and co-labeled amoeba like somata are presented. (6) CCL2-ir and astrocyte marker GFAP or Iba-1 double labeled structures are also observed within the ependymal layer. No accumulation of neutrophils was detected.

CONCLUSION

There exist differences in the cellular distribution of the CCL2 peptide in frontal cortex GM and subcortical WM-CC, in both the physiological condition and experimental endotoxemia. Which might cause different pathological change in the GM and WM.

Roles of Ependymal Cells in the Physiology and Pathology of the Central Nervous System

Ependymal cells are indispensable components of the central nervous system (CNS). They originate from neuroepithelial cells of the neural plate and show heterogeneity, with at least three types that are localized in different locations of the CNS. As glial cells in the CNS, accumulating evidence demonstrates that ependymal cells play key roles in mammalian CNS development and normal physiological processes by controlling the production and flow of cerebrospinal fluid (CSF), brain metabolism, and waste clearance. Ependymal cells have been attached to great importance by neuroscientists because of their potential to participate in CNS disease progression. Recent studies have demonstrated that ependymal cells participate in the development and progression of various neurological diseases, such as spinal cord injury and hydrocephalus, raising the possibility that they may serve as a potential therapeutic target for the disease. This review focuses on the function of ependymal cells in the developmental CNS as well as in the CNS after injury and discusses the underlying mechanisms of controlling the functions of ependymal cells.

In vitro Immunomodulatory Effects of Human Umbilical Cord-Derived Mesenchymal Stem Cells on Peripheral Blood Cells from Warm Autoimmune Hemolytic Anemia Patients

INTRODUCTION

Autoimmune hemolytic anemia is a potentially lethal disease characterized by autoimmune hemolysis. Although human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) have been reported as a promising therapy, there is limited evidence regarding warm autoimmune hemolytic anemia (wAIHA) patients. This study aimed to investigate the potential therapeutic effects of hUC-MSCs via immune regulation in wAIHA patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) from 10 wAIHA patients and 8 healthy controls were isolated from peripheral blood and cultured for 3 days with or without the presence of hUC-MSCs; PBMCs were co-cultured with hUC-MSCs using Transwell assays. The supernatant cytokine levels were measured after culture through AimPlex Multiple Immunoassays for Flow, including IL-2, IL-4, IL-10, IFN-γ, TNF-α, and IL-17A. The percentages of regulatory T cells, regulatory B cells, and Th1/Th2 in PBMCs were also assessed before and after culturing.

RESULTS

In the wAIHA group, hUC-MSCs could upregulate the Treg and Breg proportions after culturing for 3 days, and the Treg and Breg percentages increased after co-culturing with hUC-MSCs in the wAIHA group compared with PBMC cultured alone for 3 days (8.29 ± 8.59 vs. 6.82 ± 1.32, 3.82 ± 1.87 vs. 1.75 ± 1.20, respectively). Compared with the PBMC wAIHA group, the levels of TNF-α (2.13 ± 2.07 vs. 16.20 ± 21.13 pg/mL, p = 0.019) and IL-10 (10.51 ± 18.42 vs. 37.78 ± 44.20 pg/mL, p = 0.012) were significantly elevated in the PBMC + hUC-MSCs wAIHA group.

CONCLUSION

The hUC-MSCs contributed to the increasing proportion of regulatory cell populations in PBMCs of wAIHA patients, thereby potentially regulating autoimmune response; thus, hUC-MSCs may be a promising approach for wAIHA treatment.

Microglia activated by microbial neuraminidase contributes to ependymal cell death

The administration of microbial neuraminidase into the brain ventricular cavities of rodents represents a model of acute aseptic neuroinflammation. Ependymal cell death and hydrocephalus are unique features of this model. Here we demonstrate that activated microglia participates in ependymal cell death. Co-cultures of pure microglia with ependymal cells (both obtained from rats) were performed, and neuraminidase or lipopolysaccharide were used to activate microglia. Ependymal cell viability was unaltered in the absence of microglia or inflammatory stimulus (neuraminidase or lipopolysaccharide). The constitutive expression by ependymal cells of receptors for cytokines released by activated microglia, such as IL-1β, was demonstrated by qPCR. Besides, neuraminidase induced the overexpression of both receptors in ventricular wall explants. Finally, ependymal viability was evaluated in the presence of functional blocking antibodies against IL-1β and TNFα. In the co-culture setting, an IL-1β blocking antibody prevented ependymal cell death, while TNFα antibody did not. These results suggest that activated microglia are involved in the ependymal damage that occurs after the administration of neuraminidase in the ventricular cavities, and points to IL-1β as possible mediator of such effect. The relevance of these results lies in the fact that brain infections caused by neuraminidase-bearing pathogens are frequently associated to ependymal death and hydrocephalus.

Microglial activation by microbial neuraminidase through TLR2 and TLR4 receptors

Background

Neuraminidase (NA) is a sialidase present, among various locations, in the envelope/membrane of some bacteria/viruses (e.g., influenza virus), and is involved in infectiveness and/or dispersion. The administration of NA within the brain lateral ventricle represents a model of acute sterile inflammation. The relevance of the Toll-like receptors TLR2 and TLR4 (particularly those in microglial cells) in such process was investigated.

Methods

Mouse strains deficient in either TLR2 (TLR2^-/-) or TLR4 (TLR4^-/-) were used. NA was injected in the lateral ventricle, and the inflammatory reaction was studied by immunohistochemistry (IBA1 and IL-1β) and qPCR (cytokine response). Also, microglia was isolated from those strains and in vitro stimulated with NA, or with TLR2/TLR4 agonists as positive controls (P3C and LPS respectively). The relevance of the sialidase activity of NA was investigated by stimulating microglia with heat-inactivated NA, or with native NA in the presence of sialidase inhibitors (oseltamivir phosphate and N-acetyl-2,3-dehydro-2-deoxyneuraminic acid).

Results

In septofimbria and hypothalamus, IBA1-positive and IL-1β-positive cell counts increased after NA injection in wild type (WT) mice. In TLR4^-/- mice, such increases were largely abolished, while were only slightly diminished in TLR2^-/- mice. Similarly, the NA-induced expression of IL-1β, TNFα, and IL-6 was completely blocked in TLR4^-/- mice, and only partially reduced in TLR2^-/- mice. In isolated cultured microglia, NA induced a cytokine response (IL-1β, TNFα, and IL-6) in WT microglia, but was unable to do so in TLR4^-/- microglia; TLR2 deficiency partially affected the NA-induced microglial response. When WT microglia was exposed in vitro to heat-inactivated NA or to native NA along with sialidase inhibitors, the NA-induced microglia activation was almost completely abrogated.

Conclusions

NA is able to directly activate microglial cells, and it does so mostly acting through the TLR4 receptor, while TLR2 has a secondary role. Accordingly, the inflammatory reaction induced by NA in vivo is partially dependent on TLR2, while TLR4 plays a crucial role. Also, the sialidase activity of NA is critical for microglial activation. These results highlight the relevance of microbial NA in the neuroinflammation provoked by NA-bearing pathogens and the possibility of targeting its sialidase activity to ameliorate its impact.

Microglial Morphometric Parameters Correlate With the Expression Level of IL-1β, and Allow Identifying Different Activated Morphotypes

Microglia are the resident macrophages in the brain. Traditionally, two forms of microglia have been described: one considered as a resting/surveillant state in which cells have a highly branched morphology, and another considered as an activated state in which they acquire a de-ramified or amoeboid form. However, many studies describe intermediate microglial morphologies which emerge during pathological processes. Since microglial form and function are closely related, it is of interest to correlate microglial morphology with the extent of its activation. To address this issue, we used a rat model of neuroinflammation consisting in a single injection of the enzyme neuraminidase (NA) within the lateral ventricle. Sections from NA-injected animals were co-immunolabeled with the microglial marker IBA1 and the cytokine IL-1β, which highlight features of the cell’s shape and inflammatory activation, respectively. Activated (IL-1β positive) microglial cells were sampled from the dorsal hypothalamus nearby the third ventricle. Images of single microglial cells were processed in two different ways to obtain (1) an accurate measure of the level of expression of IL-1β (indicating the degree of activation), and (2) a set of 15 morphological parameters to quantitatively and objectively describe the cell’s shape. A simple regression analysis revealed a dependence of most of the morphometric parameters on IL-1β expression, demonstrating that the morphology of microglial cells changes progressively with the degree of activation. Moreover, a hierarchical cluster analysis pointed out four different morphotypes of activated microglia, which are characterized not only by morphological parameters values, but also by specific IL-1β expression levels. Thus, these results demonstrate in an objective manner that the activation of microglial cells is a gradual process, and correlates with their morphological change. Even so, it is still possible to categorize activated cells according to their morphometric parameters, each category presenting a different activation degree. The physiological relevance of those activated morphotypes is an issue worth to be assessed in the future.

SVCT2 Expression and Function in Reactive Astrocytes Is a Common Event in Different Brain Pathologies

Ascorbic acid (AA), the reduced form of vitamin C, acts as a neuroprotector by eliminating free radicals in the brain. Sodium/vitamin C co-transporter isoform 2 (SVCT2) mediates uptake of AA by neurons. It has been reported that SVCT2 mRNA is induced in astrocytes under ischemic damage, suggesting that its expression is enhanced in pathological conditions. However, it remains to be established if SVCT expression is altered in the presence of reactive astrogliosis generated by different brain pathologies. In the present work, we demonstrate that SVCT2 expression is increased in astrocytes present at sites of neuroinflammation induced by intracerebroventricular injection of a GFP-adenovirus or the microbial enzyme, neuraminidase. A similar result was observed at 5 and 10 days after damage in a model of traumatic injury and in the hippocampus and cerebral cortex in the in vivo kindling model of epilepsy. Furthermore, we defined that cortical astrocytes maintained in culture for long periods acquire markers of reactive gliosis and express SVCT2, in a similar way as previously observed in situ. Finally, by means of second harmonic generation and 2-photon fluorescence imaging, we analyzed brain necropsied material from patients with Alzheimer's disease (AD), which presented with an accumulation of amyloid plaques. Strikingly, although AD is characterized by focalized astrogliosis surrounding amyloid plaques, SVCT2 expression at the astroglial level was not detected. We conclude that SVCT2 is heterogeneously induced in reactive astrogliosis generated in different pathologies affecting the central nervous system (CNS).

Microglia Morphological Categorization in a Rat Model of Neuroinflammation by Hierarchical Cluster and Principal Components Analysis

It is known that microglia morphology and function are closely related, but only few studies have objectively described different morphological subtypes. To address this issue, morphological parameters of microglial cells were analyzed in a rat model of aseptic neuroinflammation. After the injection of a single dose of the enzyme neuraminidase (NA) within the lateral ventricle (LV) an acute inflammatory process occurs. Sections from NA-injected animals and sham controls were immunolabeled with the microglial marker IBA1, which highlights ramifications and features of the cell shape. Using images obtained by section scanning, individual microglial cells were sampled from various regions (septofimbrial nucleus, hippocampus and hypothalamus) at different times post-injection (2, 4 and 12 h). Each cell yielded a set of 15 morphological parameters by means of image analysis software. Five initial parameters (including fractal measures) were statistically different in cells from NA-injected rats (most of them IL-1β positive, i.e., M1-state) compared to those from control animals (none of them IL-1β positive, i.e., surveillant state). However, additional multimodal parameters were revealed more suitable for hierarchical cluster analysis (HCA). This method pointed out the classification of microglia population in four clusters. Furthermore, a linear discriminant analysis (LDA) suggested three specific parameters to objectively classify any microglia by a decision tree. In addition, a principal components analysis (PCA) revealed two extra valuable variables that allowed to further classifying microglia in a total of eight sub-clusters or types. The spatio-temporal distribution of these different morphotypes in our rat inflammation model allowed to relate specific morphotypes with microglial activation status and brain location. An objective method for microglia classification based on morphological parameters is proposed.

Main points

Microglia undergo a quantifiable morphological change upon neuraminidase induced inflammation.

Hierarchical cluster and principal components analysis allow morphological classification of microglia.

Brain location of microglia is a relevant factor.

Microbial Neuraminidase Induces a Moderate and Transient Myelin Vacuolation Independent of Complement System Activation

AIMS

Some central nervous system pathogens express neuraminidase (NA) on their surfaces. In the rat brain, a single intracerebroventricular (ICV) injection of NA induces myelin vacuolation in axonal tracts. Here, we explore the nature, the time course, and the role of the complement system in this damage.

METHODS

The spatiotemporal analysis of myelin vacuolation was performed by optical and electron microscopy. Myelin basic protein-positive area and oligodendrocyte transcription factor (Olig2)-positive cells were quantified in the damaged bundles. Neuronal death in the affected axonal tracts was assessed by Fluoro-Jade B and anti-caspase-3 staining. To evaluate the role of the complement, membrane attack complex (MAC) deposition on damaged bundles was analyzed using anti-C5b9. Rats ICV injected with the anaphylatoxin C5a were studied for myelin damage. In addition, NA-induced vacuolation was studied in rats with different degrees of complement inhibition: normal rats treated with anti-C5-blocking antibody and C6-deficient rats.

RESULTS

The stria medullaris, the optic chiasm, and the fimbria were the most consistently damaged axonal tracts. Vacuolation peaked 7 days after NA injection and reverted by day 15. Olig2+ cell number in the damaged tracts was unaltered, and neurodegeneration associated with myelin alterations was not detected. MAC was absent on damaged axonal tracts, as revealed by C5b9 immunostaining. Rats ICV injected with the anaphylatoxin C5a displayed no myelin injury. When the complement system was experimentally or constitutively inhibited, NA-induced myelin vacuolation was similar to that observed in normal rats.

CONCLUSION

Microbial NA induces a moderate and transient myelin vacuolation that is not caused either by neuroinflammation or complement system activation.

The Effect of Stereotactic Injections on Demyelination and Remyelination: a Study in the Cuprizone Model

Remyelination is the natural repair mechanism in demyelinating disorders of the central nervous system (CNS) such as multiple sclerosis. Several animal models have been used to study demyelination and remyelination. Among toxic animal models, oral administration of the toxin cuprizone leads to white and gray matter demyelination. In contrast, focal demyelination models include the stereotactic application of a toxin such as lysolecithin or ethidium bromide. The injection procedure generates a local disruption of the blood-brain barrier (BBB) and might thus trigger a local inflammatory reaction and consequently may influence demyelination and remyelination. In order to study such consequences, we applied stereotactic injections in the cuprizone model where demyelination and remyelination are mediated independent of this procedure. Immunohistochemistry was performed to detect the presence of lymphocytes and activated glial cells in the injection area. Blood protein stainings were used to assess the integrity of the BBB and myelin staining to evaluate demyelination and remyelination processes. Stereotactic injection led to a local disruption of the BBB as shown by local extravasation of blood proteins. Along the injection canal, T and B lymphocytes could be detected and there was a tendency of a higher microgliosis and astrocytosis. However, these changes did not influence demyelination and remyelination processes at the site of injection, in the corpus callosum, or in the cerebral cortex. Our results suggest that a local stereotactic injection has no major impact on CNS demyelination and remyelination.

Complement system activation contributes to the ependymal damage induced by microbial neuraminidase

Background

In the rat brain, a single intracerebroventricular injection of neuraminidase from Clostridium perfringens induces ependymal detachment and death. This injury occurs before the infiltration of inflammatory blood cells; some reports implicate the complement system as a cause of these injuries. Here, we set out to test the role of complement.

Methods

The assembly of the complement membrane attack complex on the ependymal epithelium of rats injected with neuraminidase was analyzed by immunohistochemistry. Complement activation, triggered by neuraminidase, and the participation of different activation pathways were analyzed by Western blot. In vitro studies used primary cultures of ependymal cells and explants of the septal ventricular wall. In these models, ependymal cells were exposed to neuraminidase in the presence or absence of complement, and their viability was assessed by observing beating of cilia or by trypan blue staining. The role of complement in ependymal damage induced by neuraminidase was analyzed in vivo in two rat models of complement blockade: systemic inhibition of C5 by using a function blocking antibody and testing in C6-deficient rats.

Results

The complement membrane attack complex immunolocalized on the ependymal surface in rats injected intracerebroventricularly with neuraminidase. C3 activation fragments were found in serum and cerebrospinal fluid of rats treated with neuraminidase, suggesting that neuraminidase itself activates complement. In ventricular wall explants and isolated ependymal cells, treatment with neuraminidase alone induced ependymal cell death; however, the addition of complement caused increased cell death and disorganization of the ependymal epithelium. In rats treated with anti-C5 and in C6-deficient rats, intracerebroventricular injection of neuraminidase provoked reduced ependymal alterations compared to non-treated or control rats. Immunohistochemistry confirmed the absence of membrane attack complex on the ependymal surfaces of neuraminidase-exposed rats treated with anti-C5 or deficient in C6.

Conclusions

These results demonstrate that the complement system contributes to ependymal damage and death caused by neuraminidase. However, neuraminidase alone can induce moderate ependymal damage without the aid of complement.