Post-embedding cytochemistry with gold-labelled reagents: a review

Neutrophil extracellular traps in CSF and serum of dogs with steroid-responsive meningitis-arteritis

In steroid-responsive meningitis-arteritis (SRMA), inflammatory dysregulation is driven by neutrophilic granulocytes resulting in purulent leptomeningitis. Neutrophils can generate neutrophil extracellular traps (NET). Uncontrolled NET-formation or impaired NET-clearance evidently cause tissue and organ damage resulting in immune-mediated diseases. The aim of the study was to verify that NET-formation is detectable in ex vivo samples of acute diseased dogs with SRMA by visualizing and measuring NET-markers in serum and cerebrospinal fluid (CSF) samples. CSF-samples of dogs with acute SRMA (n = 5) and in remission (n = 4) were examined using immunofluorescence (IF)-staining of DNA-histone-1-complexes, myeloperoxidase and citrullinated Histone H3 (H3Cit). Immunogold-labeling of H3Cit and neutrophil elastase followed by transmission electron microscopy (TEM) were used to determine ultrastructural NET-formation in the CSF of one exemplary dog. H3Cit-levels and DNase-activity were measured in CSF and serum samples using an H3Cit-ELISA and a DNase-activity-assay, respectively in patients with the following diseases: acute SRMA (n = 34), SRMA in remission (n = 4), bacterial encephalitis (n = 3), meningioma with neutrophilic inflammation (n = 4), healthy dogs (n = 6). NET-formation was detectable with IF-staining in n = 3/5 CSF samples of dogs with acute SRMA but were not detectable during remission. Vesicular NET-formation was detectable in one exemplary dog using TEM. DNase-activity was significantly reduced in dogs suffering from acute SRMA compared to healthy control group (p < 0.0001). There were no statistical differences of H3Cit levels in CSF or serum samples of acute diseased dogs compared to dogs under treatment, dogs suffering from meningioma or bacterial encephalitis or the healthy control group. Our findings demonstrate that NET-formation and insufficient NET-clearance possibly drive the immunologic dysregulation and complement the pathogenesis of SRMA. The detection of NETs in SRMA offers many possibilities to explore the aetiopathogenetic influence of this defence mechanism of the innate immune system in infectious and non-infectious canine neuropathies.

Mycobacterium tuberculosis PE/PPE proteins enhance the production of reactive oxygen species and formation of neutrophil extracellular traps

Introduction

Neutrophil granulocytes predominate in the lungs of patients infected with Mycobacterium tuberculosis (Mtb) in earlier stages of the disease. During infection, neutrophils release neutrophil extracellular traps (NETs), an antimicrobial mechanism by which a DNA-backbone spiked with antimicrobial components traps the mycobacteria. However, the specific mycobacterial factors driving NET formation remain unclear. Proteins from the proline-glutamic acid (PE)/proline-proline-glutamic acid (PPE) family are critical to Mtb pathophysiology and virulence.

Methods

Here, we investigated NET induction by PE18, PPE26, and PE31 in primary human blood-derived neutrophils. Neutrophils were stimulated with the respective proteins for 3h, and NET formation was subsequently assessed using confocal fluorescence microscopy. Intracellular ROS levels and cell necrosis were estimated by flow cytometry. Additionally, the influence of phorbol-12-myristate-13-acetate (PMA), a known NADPH oxidase enhancer, on NET formation was examined. Neutrophil integrity following incubation with the PE/PPE proteins was evaluated using transmission electron microscopy.

Results

For the first time, we report that stimulation of primary human blood-derived neutrophils with Mtb proteins PE18, PPE26, and PE31 resulted in the formation of NETs, which correlated with an increase in intracellular ROS levels. Notably, the presence of PMA further amplified this effect. Following incubation with the PE/PPE proteins, neutrophils were found to remain viable and structurally intact, as verified through transmission electron microscopy, indicating the occurrence of vital NET formation.

Discussion

These findings offer valuable insights that contribute to a better understanding of host-pathogen interactions during Mtb infection. Moreover, they underscore the significance of these particular Mtb antigens in triggering NET formation, representing a distinctive and previously unrecognized function of PE/PPE antigens.

The dynamic nature of netrin-1 and the structural basis for glycosaminoglycan fragment-induced filament formation

Netrin-1 is a bifunctional chemotropic guidance cue that plays key roles in diverse cellular processes including axon pathfinding, cell migration, adhesion, differentiation, and survival. Here, we present a molecular understanding of netrin-1 mediated interactions with glycosaminoglycan chains of diverse heparan sulfate proteoglycans (HSPGs) and short heparin oligosaccharides. Whereas interactions with HSPGs act as platform to co-localise netrin-1 close to the cell surface, heparin oligosaccharides have a significant impact on the highly dynamic behaviour of netrin-1. Remarkably, the monomer-dimer equilibrium of netrin-1 in solution is abolished in the presence of heparin oligosaccharides and replaced with highly hierarchical and distinct super assemblies leading to unique, yet unknown netrin-1 filament formation. In our integrated approach we provide a molecular mechanism for the filament assembly which opens fresh paths towards a molecular understanding of netrin-1 functions.

New Insights into Neutrophil Extracellular Trap (NETs) Formation from Porcine Neutrophils in Response to Bacterial Infections

Actinobacillus pleuropneumoniae (A.pp, Gram negative) and Streptococcus (S.) suis (Gram positive) can cause severe diseases in pigs. During infection, neutrophils infiltrate to counteract these pathogens with phagocytosis and/or neutrophil extracellular traps (NETs). NETs consist of a DNA-backbone spiked with antimicrobial components. The NET formation mechanisms in porcine neutrophils as a response to both of the pathogens are not entirely clear. The aim of this study was to investigate whether A.pp (serotype 2, C3656/0271/11) and S. suis (serotype 2, strain 10) induce NETs by NADPH oxidase- or CD18-dependent mechanisms and to characterize phenotypes of NETs in porcine neutrophils. Therefore, we investigated NET induction in porcine neutrophils in the presence and absence of NET inhibitors and quantified NETs after 3 h. Furthermore, NETosis and phagocytosis were investigated by transmission electron microscopy after 30 min to characterize different phenotypes. A.pp and S. suis induce NETs that are mainly ROS-dependent. A.pp induces NETs that are partially CD18-dependent. Thirty minutes after infection, both of the pathogens induced a vesicular NET formation with only slight differences. Interestingly, some neutrophils showed only NET-marker positive phagolysosomes, but no NET-marker positive vesicles. Other neutrophils showed vesicular NETs and only NET-marker negative phagolysosomes. In conclusion, both of the pathogens induce ROS-dependent NETs. Vesicular NETosis and phagocytosis occur in parallel in porcine neutrophils in response to S. suis serotype 2 and A.pp serotype 2.

Immuno-gold Techniques in Biomedical Sciences

Since their development in the 1960s, immuno-gold techniques have been steadily used in biomedical science, because these techniques are applicable to all kinds of antigens, from viruses to animal tissues. Immuno-gold staining exploits antigen-antibody reactions and is used to investigate locations and interactions of components in the ultrastructure of tissues, cells, and particles. These methods are increasingly used with advanced technologies, such as correlative light and electron microscopy and cryo-techniques. In this protocol, we introduce the principles and technical details of recent advances in this area and discuss their advantages and limitations.

Neutrophil Extracellular Traps in the Pathogenesis of Equine Recurrent Uveitis (ERU)

Equine recurrent uveitis (ERU) is considered one of the most important eye diseases in horses and typically appears with relapsing inflammatory episodes without systemic effects. Various disorders have been described as an initial trigger, including infections. Independent of the initiating cause, there are numerous indications that ERU is an immune-mediated disease. We investigated whether neutrophil extracellular traps (NETs) are part of the ERU pathogenesis. Therefore, vitreous body fluids (VBF), sera, and histological sections of the eye from ERU-diseased horses were analyzed for the presence of NET markers and compared with horses with healthy eyes. In addition, NET formation by blood derived neutrophils was investigated in the presence of VBF derived from horses with healthy eyes versus ERU-diseased horses using immunofluorescence microscopy. Interestingly, NET markers like free DNA, histone-complexes, and myeloperoxidase were detected in higher amounts in samples from ERU-diseased horses. Furthermore, in vitro NET formation was higher in neutrophils incubated with VBF from diseased horses compared with those animals with healthy eyes. Finally, we characterized the ability of equine cathelicidins to induce NETs, as potential NET inducing factors in ERU-diseased horses. In summary, our findings lead to the hypothesis that ERU-diseased horses develop more NETs and that these may contribute to the pathogenesis of ERU.

The heme and radical scavenger α1-microglobulin (A1M) confers early protection of the immature brain following preterm intraventricular hemorrhage

Background

Germinal matrix intraventricular hemorrhage (GM-IVH) is associated with cerebro-cerebellar damage in very preterm infants, leading to neurodevelopmental impairment. Penetration, from the intraventricular space, of extravasated red blood cells and extracellular hemoglobin (Hb), to the periventricular parenchyma and the cerebellum has been shown to be causal in the development of brain injury following GM-IVH. Furthermore, the damage has been described to be associated with the cytotoxic nature of extracellular Hb-metabolites. To date, there is no therapy available to prevent infants from developing either hydrocephalus or serious neurological disability. Mechanisms previously described to cause brain damage following GM-IVH, i.e., oxidative stress and Hb-metabolite toxicity, suggest that the free radical and heme scavenger α₁-microglobulin (A1M) may constitute a potential neuroprotective intervention.

Methods

Using a preterm rabbit pup model of IVH, where IVH was induced shortly after birth in pups delivered by cesarean section at E29 (3 days prior to term), we investigated the brain distribution of recombinant A1M (rA1M) following intracerebroventricular (i.c.v.) administration at 24 h post-IVH induction. Further, short-term functional protection of i.c.v.-administered human A1M (hA1M) following IVH in the preterm rabbit pup model was evaluated.

Results

Following i.c.v. administration, rA1M was distributed in periventricular white matter regions, throughout the fore- and midbrain and extending to the cerebellum. The regional distribution of rA1M was accompanied by a high co-existence of positive staining for extracellular Hb.

Administration of i.c.v.-injected hA1M was associated with decreased structural tissue and mitochondrial damage and with reduced mRNA expression for proinflammatory and inflammatory signaling-related genes induced by IVH in periventricular brain tissue.

Conclusions

The results of this study indicate that rA1M/hA1M is a potential candidate for neuroprotective treatment following preterm IVH.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1486-4) contains supplementary material, which is available to authorized users.

Visualization of internal in situ cell structure by atomic force microscopy

Light and electron microscopy have been used to study cell structure for many years, but atomic force microscopy is a more recent technique used to analyze cells, mainly due to the absence of techniques to prepare the samples. Isolated molecules or organelles, whole cells, and to a lesser extent in situ cell structure have been observed by different atomic force microscopy imaging modes. Here, we review efforts intended to analyze in situ the cell structures using approaches involving imaging of the surface of semithin sections of samples embedded in resin and sections prepared with an ultramicrotome. The results of such studies are discussed in relation to their implications to analyze the fine structure of organelles at the nanoscale in situ at enhanced resolution compared to light microscopy.

The cell wall DUF642 At2g41800 (TEB) protein is involved in hypocotyl cell elongation

In plants, the cell wall is a complex and dynamic structure comprising high molecular weight carbohydrates and proteins. The cell wall plays an important role in several stages of the plant life cycle, including cell division, elongation and differentiation. The DUF642 family of cell wall proteins is highly conserved in spermatophytes and might be involved in pectin structural modifications. Particularly, At2g41800 is one of the most highly induced genes during the M/G1 phases of the cell cycle, and the protein encodes by this gene has been detected in cell wall proteomes of cell suspension cultures. In the present study, the expression of At2g41800 (TEB) was confirmed in primary and lateral roots, stigmatic papillae and hypocotyls. Subcellular localization studies showed that TEB is located in the cell wall. The root length and lateral root density were not affected in either of the two teb mutants studied, but the length of the hypocotyls from seedlings grown under light and dark conditions was increased. Immunogold labelling studies using JIM5 antibodies on sections of hypocotyl epidermal cells showed an important reduction of gold particles in teb mutants. The results suggested that TEB is involved in hypocotyl elongation.

Interactome Mapping Reveals the Evolutionary History of the Nuclear Pore Complex

The nuclear pore complex (NPC) is responsible for nucleocytoplasmic transport and constitutes a hub for control of gene expression. The components of NPCs from several eukaryotic lineages have been determined, but only the yeast and vertebrate NPCs have been extensively characterized at the quaternary level. Significantly, recent evidence indicates that compositional similarity does not necessarily correspond to homologous architecture between NPCs from different taxa. To address this, we describe the interactome of the trypanosome NPC, a representative, highly divergent eukaryote. We identify numerous new NPC components and report an exhaustive interactome, allowing assignment of trypanosome nucleoporins to discrete NPC substructures. Remarkably, despite retaining similar protein composition, there are exceptional architectural dissimilarities between opisthokont (yeast and vertebrates) and excavate (trypanosomes) NPCs. Whilst elements of the inner core are conserved, numerous peripheral structures are highly divergent, perhaps reflecting requirements to interface with divergent nuclear and cytoplasmic functions. Moreover, the trypanosome NPC has almost complete nucleocytoplasmic symmetry, in contrast to the opisthokont NPC; this may reflect divergence in RNA export processes at the NPC cytoplasmic face, as we find evidence supporting Ran-dependent mRNA export in trypanosomes, similar to protein transport. We propose a model of stepwise acquisition of nucleocytoplasmic mechanistic complexity and demonstrate that detailed dissection of macromolecular complexes provides fuller understanding of evolutionary processes.

Dissection of the nuclear pore complex—an ancient eukaryotic molecular machine—exposes a fundamental divergence in structure and function between yeast and humans versus trypanosomes and provides insights into the evolution of the nucleus.

Much of the core architecture of the eukaryotic cell was established over one billion years ago. Significantly, many cellular systems possess lineage-specific features, and architectural and compositional variation of complexes and pathways that are likely keyed to specific functional adaptations. The nuclear pore complex (NPC) contributes to many processes, including nucleocytoplasmic transport, interactions with the nuclear lamina, and mRNA processing. We exploited trypanosome parasites to investigate NPC evolution and conservation at the level of protein–protein interactions and composition. We unambiguously assigned NPC components to specific substructures and found that the NPC structural scaffold is generally conserved, albeit with lineage-specific elements. However, there is significant variation in pore membrane proteins and an absence of critical components involved in mRNA export in fungi and animals (opisthokonts). This is reflected by the completely symmetric localization of all trypanosome nucleoporins, with the exception of the nuclear basket. This architecture is highly distinct from opisthokonts. We also identify features that suggest a Ran-dependent system for mRNA export in trypanosomes, a system that may presage distinct mechanisms of protein and mRNA transport in animals and fungi. Our study highlights that shared composition of macromolecular assemblies does not necessarily equate to shared architecture. Identification of lineage-specific features within the trypanosome NPC significantly advances our understanding of mechanisms of nuclear transport, gene expression, and evolution of the nucleus.

Extracellular hemoglobin - mediator of inflammation and cell death in the choroid plexus following preterm intraventricular hemorrhage

BACKGROUND

Intraventricular hemorrhage (IVH) with post-hemorrhagic ventricular dilatation (PHVD) is a major cause of neurodevelopmental impairment and mortality in preterm infants. The mechanisms leading to PHVD and brain damage remain largely unknown. The choroid plexus and the ependyma, which constitute an essential part of the blood-brain barrier (BBB), are the first structures to encounter the damaging effects of extravasated blood. The breakdown of the BBB is a critical upstream event leading to brain damage following IVH. In this study we investigated the impact of hemorrhage and hemoglobin (Hb) metabolites on the choroid plexus epithelium.

METHODS

Using a preterm rabbit pup model of IVH, the structural and functional integrity, cellular, inflammatory and oxidative response of the choroid plexus, at 24 and 72 hours following IVH + PHVD, were investigated. In order to further characterize cellular and molecular mechanisms, primary human choroid plexus epithelial cells were exposed to cerebrospinal fluid (CSF) from preterm infants with IVH as well as to Hb-metabolites. Finally, the blocking effects of the Hb-scavenger haptoglobin (Hp) were investigated both in vivo and in vitro.

RESULTS

Following IVH + PHVD, an up-regulation of mRNA for the receptor-related genes TLR-4, IL1R1, FAS, the transcription factor NF-Κβ and for the pro-inflammatory and chemotactic effector molecules, IL-1β, TNFα, MCP-1, IL-8, and IL-6 was observed in the choroid plexus at 24 and 72 hours. This was associated with structural disintegration, caspase activation and cell death in the choroid plexus epithelium. In vitro characterization of choroid plexus epithelial cells, following exposure to hemorrhagic CSF and to the Hb-metabolites metHb and heme, displayed apoptotic and necrotic cell death and an up-regulation of receptor-related and inflammatory effector molecules similar to that observed in vivo following IVH + PHVD. Intraventricular injection of the Hb-scavenger Hp in vivo and co-incubation with Hp in vitro reversed or reduced the cellular activation, inflammatory response, structural damage and cell death.

CONCLUSION

Hb-metabolites are important causal initiators of cell death following IVH and removal or scavenging of Hb-metabolites may present an efficient means to reduce the damage to the immature brain following IVH.

Altered expression of aquaporin 1 and 5 in the choroid plexus following preterm intraventricular hemorrhage

Intraventricular hemorrhage (IVH) with posthemorrhagic ventricular dilatation (PHVD) is a common cause of hydrocephalus in infants. Dysregulation of cerebrospinal fluid (CSF) production by the choroid plexus may contribute to the development of PHVD. The aquaporins (AQPs), transmural water transporting proteins, are believed to contribute to CSF production. The aim of the study was to characterize the expression and localization of AQP1, 4 and 5 in the choroid plexus following preterm IVH. Using a preterm rabbit pup model, the mRNA expression, protein level and localization of AQP1, 4 and 5 were investigated in the choroid plexus at 24 and 72 h following IVH with PHVD. Further, AQP1, 4 and 5 expression were characterized in primary human plexus epithelial cells exposed to CSF from preterm human infants with IVH and to hemoglobin metabolites. IVH with PHVD in the immature brain caused a downregulation of AQP1 mRNA, the key AQP in CSF production, but an upregulation of AQP1 protein level with apical epithelial cell localization. Notably, AQP5 was expressed in the choroid plexus with upregulated mRNA expression and protein levels during PHVD with apical epithelial cell localization. Analysis of human choroid plexus epithelial cells in vitro, following exposure to posthemorrhagic CSF and to hemin, displayed results concordant with those observed in vivo, i.e. downregulation of AQP1 mRNA and upregulation of AQP5 mRNA expression. AQP4 was neither detectable in vivo nor in vitro. The changes observed in AQP1 and AQP5 expression in the choroid plexus suggest an adaptive response following IVH with possible functional implications for the development of PHVD.

IG20/MADD plays a critical role in glucose-induced insulin secretion

Pancreatic β-cell dysfunction is a common feature of type 2 diabetes. Earlier, we had cloned IG20 cDNA from a human insulinoma and had shown that IG20/MADD can encode six different splice isoforms that are differentially expressed and have unique functions, but its role in β-cell function was unexplored. To investigate the role of IG20/MADD in β-cell function, we generated conditional knockout (KMA1ko) mice. Deletion of IG20/MADD in β-cells resulted in hyperglycemia and glucose intolerance associated with reduced and delayed glucose-induced insulin production. KMA1ko β-cells were able to process insulin normally but had increased insulin accumulation and showed a severe defect in glucose-induced insulin release. These findings indicated that IG20/MADD plays a critical role in glucose-induced insulin release from β-cells and that its functional disruption can cause type 2 diabetes. The clinical relevance of these findings is highlighted by recent reports of very strong association of the rs7944584 single nucleotide polymorphism (SNP) of IG20/MADD with fasting hyperglycemia/diabetes. Thus, IG20/MADD could be a therapeutic target for type 2 diabetes, particularly in those with the rs7944584 SNP.

The radical-binding lipocalin A1M binds to a Complex I subunit and protects mitochondrial structure and function

AIMS

During cell death, energy-consuming cell degradation and recycling programs are performed. Maintenance of energy delivery during cell death is therefore crucial, but the mechanisms to keep the mitochondrial functions intact during these processes are poorly understood. We have investigated the hypothesis that the heme- and radical-binding ubiquitous protein α1-microglobulin (A1M) is involved in protection of the mitochondria against oxidative insult during cell death.

RESULTS

Using blood cells, keratinocytes, and liver cells, we show that A1M binds with high affinity to apoptosis-induced cells and is localized to mitochondria. The mitochondrial Complex I subunit NDUFAB1 was identified as a major molecular target of the A1M binding. Furthermore, A1M was shown to inhibit the swelling of mitochondria, and to reverse the severely abrogated ATP-production of mitochondria when exposed to heme and reactive oxygen species (ROS).

INNOVATION

Import of the radical- and heme-binding protein A1M from the extracellular compartment confers protection of the mitochondrial structure and function during cellular insult.

CONCLUSION

A1M binds to a subunit of Complex I and has a role in assisting the mitochondria to maintain its energy delivery during cell death. A1M may also, at the same time, counteract and eliminate the ROS generated by the mitochondrial respiration to prevent oxidative damage to surrounding healthy tissue.

Up-regulation of A1M/α1-microglobulin in skin by heme and reactive oxygen species gives protection from oxidative damage

During bleeding the skin is subjected to oxidative insults from free heme and radicals, generated from extracellular hemoglobin. The lipocalin α₁-microglobulin (A1M) was recently shown to have reductase properties, reducing heme-proteins and other substrates, and to scavenge heme and radicals. We investigated the expression and localization of A1M in skin and the possible role of A1M in the protection of skin tissue from damage induced by heme and reactive oxygen species. Skin explants, keratinocyte cultures and purified collagen I were exposed to heme, reactive oxygen species, and/or A1M and investigated by biochemical methods and electron microscopy. The results demonstrate that A1M is localized ubiquitously in the dermal and epidermal layers, and that the A1M-gene is expressed in keratinocytes and up-regulated after exposure to heme and reactive oxygen species. A1M inhibited the heme- and reactive oxygen species-induced ultrastructural damage, up-regulation of antioxidation and cell cycle regulatory genes, and protein carbonyl formation in skin and keratinocytes. Finally, A1M bound to purified collagen I (K_d = 0.96×10⁻⁶ M) and could inhibit and repair the destruction of collagen fibrils by heme and reactive oxygen species. The results suggest that A1M may have a physiological role in protection of skin cells and matrix against oxidative damage following bleeding.

Antigen retrieval causes protein unfolding: evidence for a linear epitope model of recovered immunoreactivity

Antigen retrieval (AR), in which formalin-fixed paraffin-embedded tissue sections are briefly heated in buffers at high temperature, often greatly improves immunohistochemical staining. An important unresolved question regarding AR is how formalin treatment affects the conformation of protein epitopes and how heating unmasks these epitopes for subsequent antibody binding. The objective of the current study was to use model proteins to determine the effect of formalin treatment on protein conformation and thermal stability in relation to the mechanism of AR. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was used to identify the presence of protein formaldehyde cross-links, and circular dichroism spectropolarimetry was used to determine the effect of formalin treatment and high-temperature incubation on the secondary and tertiary structure of the model proteins. Results revealed that for some proteins, formalin treatment left the native protein conformation unaltered, whereas for others, formalin denatured tertiary structure, yielding a molten globule protein. In either case, heating to temperatures used in AR methods led to irreversible protein unfolding, which supports a linear epitope model of recovered protein immunoreactivity. Consequently, the core mechanism of AR likely centers on the restoration of normal protein chemical composition coupled with improved accessibility to linear epitopes through protein unfolding.

Erysipelas caused by group A streptococcus activates the contact system and induces the release of heparin-binding protein

Bacterial skin infections, such as erysipelas or cellulitis, are characterized by fever and a painful erythematous rash. Despite the high prevalence of these infections, little is known about the underlying pathogenic mechanisms. This is partly due to the fact that a bacterial diagnosis is often difficult to attain. To gain insight into the pathogenesis of erysipelas, we investigated the samples obtained from infected and noninfected areas of skin from 12 patients with erysipelas. Bacterial cultures, detection of specific streptococcal antibodies in convalescent sera, and immunohistochemical analyses of biopsies indicated group A streptococcal etiology in 11 of the 12 patients. Also, electron micrographs of erythematous skin confirmed the presence of group A streptococcal cells and showed a limited solubilization of the surface-attached M protein. Degradation of high-molecular-weight kininogen and upregulation of the bradykinin-1 receptor in inflamed tissues indicated activation of the contact system in 11 patients. Analyses of release of the vasoactive heparin-binding protein (HBP) showed increased levels in the infected as compared with the noninfected areas. The results suggest that group A streptococci induce contact activation and HBP release during skin infection, which likely contribute to the symptoms seen in erysipelas: fever, pain, erythema, and edema.

Tissue deposits of IgA-binding streptococcal M proteins in IgA nephropathy and Henoch-Schonlein purpura

IgA nephropathy (IgAN) and Henoch-Schönlein purpura (HSP) are diseases characterized by IgA deposits in the kidney and/or skin. Both may arise after upper respiratory tract infections, but the pathogenic mechanisms governing these diseases remain unclear. Patients with IgAN (n = 16) and HSP (n = 17) were included in this study aimed at examining whether IgA-binding M proteins of group A streptococci could be involved. As M proteins vary in sequence, the study focused on the IgA-binding-region (IgA-BR) of three different M proteins: M4, M22, and M60. Renal tissue from IgAN and HSP patients and skin from HSP patients were examined for deposits of streptococcal IgA-BR by immunohistochemistry and electron microscopy using specific antibodies, and a skin sample from a HSP patient was examined by mass spectrometry. IgA-BR deposits were detected in 10/16 IgAN kidneys and 7/13 HSP kidneys. Electron microscopy demonstrated deposits of IgA-BRs in the mesangial matrix and glomerular basement membrane, which colocalized with IgA. Skin samples exhibited IgA-BR deposits in 4/5 biopsies, a result confirmed by mass spectrometry in one patient. IgA-BR deposits were not detected in normal kidney and skin samples. Taken together, these results demonstrate IgA-BR from streptococcal M proteins in patient tissues. IgA-BR, would on gaining access to the circulation, encounter circulatory IgA and form a complex with IgA-Fc that could deposit in tissues and contribute to the pathogenesis of IgAN and HSP.

Immunoelectron microscopy of human spermatozoa

A number of immunocytochemical methods using various markers for electron microscopy have been developed in recent years. The immunogold technique has been especially effective in histotopochemical studies. The value of this technique for demonstrating sperm antigens results from the high electron density of gold, which makes it easily detectable under the electron microscope. The high resolution of the electron microscope permits precise localization of immunologic reactions in the sperm cell. Light microscopy findings can thus be elucidated. We tested a number of monoclonal antibodies that react with sperm antigens. Of three techniques for preparing the spermatozoa, the pre-embedding method and marking of cryoultra-microtome sections proved best.

State of the art in antigen retrieval for immunohistochemistry

The masking effects of antigens by chemical fixation, processing, embedding media interactions, represent a serious problem for immunohistochemical purposes. Fortunately, different approaches in antigen retrieval exist. These techniques are relatively recent and continuously expanding. This review focuses on the present state of the art in antigen retrieval methods for immunohistochemistry in light and electron microscopy. Moreover, a brief discussion on the chemical aspects of fixation, mechanism of retrieval, as well as its efficacy, is given.

Regulation of kinin B2 receptors by bradykinin in human lung cells

Bradykinin is a potent mediator of inflammation that has been shown to participate in allergic airway inflammation. The biologic effects of bradykinin are mediated by binding and activation of its cognate receptor, the B2receptor (B2R). In the lung fibroblast cell line IMR-90, binding of bradykinin to B2R triggers down-regulation of receptor surface expression, suggesting that bradykinin-induced inflammation is transient and self-limited. Notably, subjects with chronic airway inflammation continue to respond to BK following a first challenge. B2Rs are expressed on many different lung cell types, including airway epithelial cells. We therefore compared IMR-90 cells with the human lung epithelial cell line BEAS2B and found that B2R expression in the two cell types is differently regulated by BK. Whereas BK induces down-regulation of B2R in IMR-90 cells, the same treatment leads to up-regulation of the receptor in BEAS2B cells. These results provide a possible explanation for the potency of bradykinin in inducing ongoing airway inflammation.

Streptococcal M Protein: A Multipotent and Powerful Inducer of Inflammation

Severe infections with Streptococcus pyogenes, an important human pathogen, are associated with massive inflammatory reactions in the human host. Here we show that streptococcal M protein interacts with TLR2 on human peripheral blood monocytes. As a consequence, monocytes express the cytokines IL-6, IL-1beta, and TNF-alpha. This response is significantly increased in the presence of neutrophil-derived heparin-binding protein (HBP), which co-stimulates monocytes by interacting with CD11/CD18. Analysis of tissue biopsies from patients with necrotizing fasciitis revealed recruitment of neutrophils and monocytes to the infectious site, combined with the release of HBP. The results show that M protein, in synergy with HBP, evokes an inflammatory response that may contribute to the profound pathophysiological consequences seen in severe streptococcal infections.

Kinin receptor expression during Staphylococcus aureus infection

An inappropriate host response to invading bacteria is a critical parameter that often aggravates the outcome of an infection. Staphylococcus aureus is a major human Gram-positive pathogen that causes a wide array of community- and hospital-acquired diseases ranging from superficial skin infections to severe conditions such as staphylococcal toxic shock. Here we find that S aureus induces inflammatory reactions by modulating the expression and response of the B1 and B2 receptors, respectively. This process is initiated by a chain of events, involving staphylococcal-induced cytokine release from monocytes, bacteria-triggered contact activation, and conversion of bradykinin to its metabolite desArg(9)bradykinin. The data of the present study implicate an important and previously unknown role for kinin receptor regulation in S aureus infections.

Electron microscopy analysis of the nucleolus of Trypanosoma cruzi

The nucleolus is the main site for synthesis and processing of ribosomal RNA in eukaryotes. In mammals, plants, and yeast the nucleolus has been extensively characterized by electron microscopy, but in the majority of the unicellular eukaryotes no such studies have been performed. Here we used ultrastructural cytochemical and immunocytochemical techniques as well as three-dimensional reconstruction to analyze the nucleolus of Trypanosoma cruzi, which is an early divergent eukaryote of medical importance. In T. cruzi epimastigotes the nucleolus is a spherical intranuclear ribonucleoprotein organelle localized in a relatively central position within the nucleus. Dense fibrillar and granular components but not fibrillar centers were observed. In addition, nuclear bodies resembling Cajal bodies were observed associated to the nucleolus in the surrounding nucleoplasm. Our results provide additional morphological data to better understand the synthesis and processing of the ribosomal RNA in kinetoplastids.

Immunogold detection of co-localized neuropeptides: methodological aspects

Whatever the protocol used, electron microscopic immunogold detection still suffers from a lack of sensitivity. In rat supraoptico-posthypophyseal neurons, unlabeled secretory granules are always detectable after electron microscopic immunocytochemistry, and their real status remains questionable. To improve the sensitivity of this approach, we assessed a protocol to visualize either one or the other of co-localized neuropeptides, i.e., vasopressin or galanin, after two successive rounds of immunogold with the same primary antibody performed on both faces of the grid. The use of different-sized gold particles enabled us to visualize the respective contribution of each face of the section to the final labeling. Our results showed a moderate but significant increase in both the proportion of labeled granules and the labeling intensity. Although limited, this improvement of immunogold detection strengthens the relevance of quantitative studies at the electron microscopic level, likely to reveal fine variations of the neuron peptidergic content. However, this enhancement depended on the peptide studied. The present data confirmed a progressive decrease of vasopressin immunoreactivity, already suggested by the single-staining procedure, all along the hypothalamo-posthypophyseal tract. In contrast, labeling intensity for galanin remained steady. Finally, our double-face labeling supported a preferential routing of galanin-containing secretory granules towards dendrites.

LR white post-embedding colloidal gold method to immunostain MBP, P0, NF and S100 in glutaraldehyde fixed peripheral nerve tissue

A variety of immunocytochemical techniques are now widely used for the electron and light microscopic examination of biological samples. They are employed routinely for investigating the role of certain proteins in nervous tissue. Immunoelectron microscopic studies require the tissue to be fixed and embedded in a solid support, which may disrupt cellular structures and destroy crucial antigens. A technique of post-embedding with LR white resin has been developed, and it has been shown that certain antigens tolerate fixation with glutaraldehyde. In this study, we optimized a previous post-embedding method using low-water-miscible low-temperature embedding resin (LR white) to immunostain MBP, P0, NF and S100 proteins in peripheral nerves fixed with a relatively high concentration of glutaraldehyde found to be compatible with the morphology of normally compacted nerve fibers from humans and adult animals. The main difference in the procedures described here from previous ones is the elimination of vibratome sectioning, rendering this immunostaining technique more accessible to neuropathological laboratories using standard equipment for the ultrastructural study of peripheral nerves. It may prove of value for localization and quantification of these proteins in normal and pathological conditions.

Further ultrastructural characterization of the intranuclear ring-shaped bodies of the plant Lacandonia schismatica

Ring-shaped bodies are found in the nucleus of Lacandonia schismatica, a rare plant with the sexual organs inverted. They are 0.5-microm-diameter structures that present an electron-dense external ring surrounding a central core. Ultrastructural studies indicate that these bodies contain RNA. The external ring is labeled with antibodies against small nuclear ribonucleoproteins, suggesting that they may be involved in pre-mRNA metabolism. In the present work we further characterized these intranuclear ring-shaped structures by serial-sectioning analysis. Moreover, we tested the presence of additional molecular elements related to pre-mRNA metabolism, such as SR proteins and poly(A)(+) RNA, using immunoelectron microscopy and ultrastructural in situ hybridization. Our results show that these nuclear bodies are spherical. They contain SR proteins involved in splicing and postsplicing events and little to no poly(A)(+) RNA. We also found similar nuclear bodies in other plant and animal species. Therefore, ring-shaped bodies in L. schismatica are spherical, highly compartmentalized nuclear structures that may be involved in pre-mRNA metabolism.

Improved post-embedding immunocytochemistry of myelinated nervous tissue for electron microscopy

The particularly high lipid content of normal mature adult myelin sheaths, together with the light fixation protocols usually necessary to retain antigenicity, combine to make white matter nervous tissue an especially problematical subject for post-embedding immuno-electron microscopy using modern acrylic resins. Fixation and infiltration modifications to standard processing schedules for Lowicryl were found to greatly improve the embedding and therefore the resulting morphology. This in turn improved the signal to noise ratio by reducing the high non-specific backgrounds usually found in poorly infiltrated areas. Using Lowicryl HM20, we have been able to obtain satisfactory immunostaining for myelin basic protein with good retention of structural integrity in the myelin of both normal and lesioned adult cortico spinal tract.

Specific staining of nonpyramidal cell populations of the cerebral cortex by lectin cytochemistry on semithin sections

The pattern of lectin labeling in the cerebral cortex of the cat was studied using semithin sections. The labeling produced by some lectins (Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, wheat germ agglutinin, and succynilated-wheat germ) appeared inside every neuron as small cytoplasmic granules, probably corresponding to cisterns of endoplasmic reticulum and/or the Golgi complex. Lectins with affinity for alpha-mannosyl residues (Pisum sativum, Lens culinaris, and Concanavalin A) stained the cell surface of a subset of cortical neurons. The labeled cells were round or polygonal, medium to large neurons present in layers II-VI, exhibiting the morphological features of nonpyramidal cells. Previous lectin studies of perineuronal nets have shown that these extracellular specializations contain N-acetylgalactosamine and N-acetylglucosamine. Our results show that mannose is also a component of perineuronal nets and that lectins specific for alpha-mannose can be used as tools for the cytochemical detection of a separate class of cortical neurons, which have not yet been fully characterized. In addition, some lectins (Bandeiraea simplicifolia, Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, and succynilated-wheat germ agglutinin) specifically labeled a population of a type of microglia-related cells known as perivascular cells. The data presented here report for the first time the selective staining of perivascular cells and further support the hypothesis that they are different from typical microglial cells.

The use of monoclonal antibodies with colloidal gold-labeled probes in postembedding immunoelectron microscopy

This article focuses on procedures for the use of monoclonal antibodies (MAb) in immunoelectron microscopy (IEM) for the subcellular localization of antigens or to relate function with structure in prokaryotic and eukaryotic cells using postembedding immunoelectron microscopy techniques. The use of MAbs greatly increases the specificity and quality of information when used in combination with gold-labeled probes. Because of its specificity, the reactivity of MAb may be very sensitive to antigenic changes resulting from the process of sample preparation when performing IEM studies. Specific protocols for each particular combination of epitope/MAb must be usually specifically devised, since it is impossible to predict an experimental system that will successfully preserve structures and antigenic determinants for every combination. In this article, we discuss critical technical aspects that usually result in improved resolution when the procedure is used to identify structure in diverse prokaryotic and eukaryotic cells.

Molecular cloning of a novel myeloid granule protein

Granulocytes are recognized by the presence of granules, including primary (azurophilic) and secondary types. Each granule type contains distinct and characteristic families of enzymes. We have screened a murine bone marrow cDNA library to obtain a series of sequences corresponding to mRNAs which are both myeloid-specific and appear to be expressed only in immature bone marrow cells. A 1,160 bp sequence (B9) has been isolated, which shows restricted expression in murine bone marrow, with the highest levels in cultures enriched for promyelocytes. Translation yields a single open reading frame of 167 amino acids and a calculated MW of 19.33 kd. A single potential N-glycosylation site is present. Evaluation of the amino terminal sequence shows 2 polar amino acids flanking a hydrophobic region, suggesting a signal sequence and the possibility of post-translational modification. An extensive search of the protein data base reveals 30% identity over 90 amino acids with porcine cathelin, a cystatin-like cysteine proteinase inhibitor. This sequence identity includes conservation of the 4 cysteine residues noted in all members of the cystatin superfamily. In an attempt to further characterize this novel sequence, a polyclonal antiserum was prepared by immunization with a 20 amino acid synthetic peptide corresponding to a unique portion of the carboxy terminus. Immunoelectron microscopy localized B9 to neutrophilic granules. We have identified a novel myeloid-specific granule protein related to porcine cathelin, but showing important structural differences. This may represent the first isolated member of a new cystatin family. More importantly, the small size of the B9 gene and its tight pattern of early expression make B9 an excellent reporter molecule for the study of new factors important in myeloid differentiation.

Cyclosporine enhances the expression of TGF-beta in the juxtaglomerular cells of the rat kidney

The mediators of cyclosporine (CsA) nephrotoxicity remain ill defined. In this study, we describe evidence of increased amounts of transforming growth factor-beta (TGF-beta) in the kidneys of adult male Wistar rats treated with CsA (5 to 25 mg/kg/day) for four weeks. Localization of TGF-beta was undertaken immunocytochemically at both light and electron microscope levels and Northern blot analysis was applied to detect changes in transcription of TGF-beta. In control rats, weak to moderate immunostaining for TGF-beta was observed, in the juxtaglomerular arterioles. CsA treatment resulted in a dose-dependent increase in the number of stained afferent and interlobular arterioles and in the intensity of staining. The number of stained afferent arterioles increased from a control value of 0.21 +/- 0.08/mm2 cortex to 0.84 +/- 0.15/mm2 cortex, P < 0.01, and to 1.12 +/- 0.10/mm2 cortex, P < 0.01, in rats treated with CsA 12.5 mg/kg/day and 25 mg/kg/day, respectively. The number of interlobular arterioles stained for TGF-beta increased from a control value of 0.07 +/- 0.05/mm2 to 0.31 +/- 0.02/mm2, P < 0.05, and 0.39 +/- 0.07/mm2, P < 0.01, in rats treated with CsA, 12.5 mg/kg/day and 25 mg/kg/day, respectively. At the electron microscope level, TGF-beta was localized exclusively within the granular cells of the juxtaglomerular arterioles. Northern blot analysis suggested that this enhanced staining is due to increased transcription of TGF-beta 1. We have therefore observed an association between TGF-beta and CsA-induced nephrotoxicity. While this does not establish a causal link, it leads us to postulate that TGF-beta, alone or in combination with other growth factors, may play a role in the pathogenesis of CsA induced nephrotoxicity.

Postembedding colloidal-gold immunocytochemistry of noncollagenous extracellular matrix proteins in mineralized tissues

Immunocytochemistry is a powerful tool for investigating protein secretion, extracellular matrix assembly, and cell-matrix and matrix-matrix/mineral relationships. When applied to the tissues of bones (bone and calcified cartilage) and teeth (dentin, cementum, and enamel), where calcium phosphate-containing extracellular matrices are the predominant structural component related to their weight-bearing and masticatory roles, respectively, data from immunocytochemical studies have been prominent in advancing our understanding of mineralized tissue modeling and remodeling. The present review on the application of postembedding, colloidal-gold immunocytochemistry to mineralized tissues focuses on the advantages of this approach and relates them to conceptual, theoretical, and experimental data currently available discussing matrix-mineral interactions and extracellular matrix formation and turnover in these tissues. More specifically, data are summarized regarding the distribution and role of noncollagenous proteins in different mineralized tissues, particularly in the context of how they interface with mineral, and how this relationship might be affected by the various tissue-processing steps and immunocytochemical strategies commonly implemented to examine the distribution and function of tissue proteins. Furthermore, a technical discussion is presented that outlines several different possibilities for epitope exposure in mineralized tissues during preparation of thin sections for transmission electron microscopy. Cell biological concepts of protein secretion by cells of the mineralized tissues, and subsequent extracellular matrix assembly and organization, are illustrated by examples of high-resolution, colloidal-gold immunolabeling for osteopontin, bone sialoprotein, and osteocalcin in the collagen-based mineralized tissues and for enamel protein (amelogenin) in enamel.

Immunocytochemistry and in situ hybridization in the electron microscope: combined application in the study of virus-infected cells

The present review evaluates methods for electron microscopic immunocytochemistry and in situ hybridization, using post-embedding techniques and colloidal gold as a label. Special emphasis is given to double labeling immunocytochemistry and double in situ hybridization and to their combined application on the same specimen. Brief guidelines are presented for fixation, embedding media, the use of polyclonal and monoclonal antibodies and nucleic acid probes. Conditions for labeling and binding of antibody and nucleic acid probes to the target and protocols for direct and indirect immunodetection are discussed. Combinations of direct and indirect immunodetections in multiple labeling experiments are summarized.

Keratinocyte muscarinic acetylcholine receptors: immunolocalization and partial characterization

We have reported previously that human keratinocytes synthesize and secrete acetylcholine and that muscarinic cholinergic drugs have effects on keratinocyte proliferation, adhesion, and migration. This study defines the location of muscarinic acetylcholine receptors in human epidermis and describes some pharmacologic and molecular properties of these receptors. Confocal microscopy employing the anti-muscarinic receptor monoclonal antibody M35 visualized the receptors in the intercellular areas of normal human epidermis. Using immunoelectron microscopy, the receptors appeared to be attached to the keratinocyte plasma membranes. Functional, high-density (Bmax = 8.3 nmol/2 x 10(6) cells) and high-affinity (Kd = 21.5 nM) muscarinic receptors were demonstrated by saturable binding of the reversible radioligand [3H]quinuclidinyl benzilate to the surfaces of freshly isolated epidermal cells at 0 degrees C. Receptor proteins were separated by gel electrophoresis. An apparent isoelectric point of pH 4.3 was determined in immunoblots of sodium-cholate-solubilized receptors separated on isoelectric-focusing gels. Three protein bands, two at approximately 60 kDa and one at 95 kDa, were visualized in immunoblots of membrane-bound or solubilized receptors separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis. The covalent, irreversible ligand [3H]propylbenzilylcholine mustard confirmed these results. Thus, human keratinocytes express a heterogeneous population of muscarinic cholinergic receptors. Because human keratinocytes also express nicotinic cholinergic receptors, endogenously secreted acetylcholine may control different biologic processes in these cells by activating different types of their cholinergic receptors.

Factors affecting the efficiency of immunogold labelling of plant virus antigens in thin sections

Sections of pellets of six purified plant viruses with three different morphologies were used to examine different technical aspects of the immunogold labelling (IGL) technique. The results showed that fixation by glutaraldehyde alone was better than with osmium tetroxide post-fixation, and that Decon 75 was the best of the pretreatments tried. The study showed that different virus homologous antisera gave different results in IGL tests, and that longer incubation times with both antiserum and gold probe gave higher label densities without any increase in background label. Also, cross-absorption of the virus antisera with healthy host protein before use gave cleaner backgrounds and thus higher specificity. The work also examined the relationship between label density and amounts of visible virus. There was no correlation between the numbers of virus particles seen in sections and the numbers of gold particles; moreover, there was no apparent relationship between label density and the orientation or distribution of the virus particles in the section. The role of the embedding resin and its polymerisation temperature are also discussed.

Immunohistochemical localization of keratan sulfate and chondroitin 4- and 6-sulfate proteoglycans in subregions of the tectorial and basilar membranes

Proteoglycans containing keratan sulfate (KSPG) and 4- and 6-sulfated epitopes of chondroitin sulfate (CSPG) were identified in distinct domains of the tectorial and basilar membranes by ultrastructural immunogold labeling with monoclonal antibodies. In the tectorial membrane (TM), the highest concentration of gold particles was present in the upper fibrous layers of the limbal, middle and marginal zones with all three antibodies. Reactivity with anti-KSPG exceeded that with anti-4S and anti-6S CSPG, especially in the marginal zone. The cover net showed no reactivity for any antibody. Labeling density of gold particles with all three antibodies increased markedly from base to apex. In the basilar membrane (BM), all three PGs were most highly concentrated in regions of amorphous ground substance bordering the upper and lower filamentous bands. As in the TM, reactivity for anti-KSPG in the BM exceeded that for either CSPG antibody and staining with all three antibodies was stronger and more widespread in the apical as compared to the basal turns. These results provide the first ultrastructural demonstration of KSPG and CSPG in distinct subregions of the TM and BM. The preferential distribution and marked increase in PGs from base to apex in both TM and BM supports a role for these macromolecules in regulating structural and mechanical properties of these highly specialized extracellular membranes.

Expression of an adhesion molecule and homing in B-cell chronic lymphocytic leukaemia: I. Application of the HEV-binding assay to a clinical series

High endothelial venule (HEV)-binding of peripheral blood mononuclear cells (PBMCs) from 43 patients with B-cell chronic lymphocytic leukaemia (B-CLL) was investigated with a HEV-binding in vitro assay. Immunophenotyping of HEV-adherent PBMCs proved that most of them belonged to the B-cell proliferation. B-CLL cells stringently expressed CD44 molecules (Hermes-1, -3 and H90). The patients were subgrouped according to Binet's classification, as well as according to the organ manifestations, i.e. patients with B-cell monoclonal lymphocytosis of undetermined significance (B-MLUS) and patients with lymphocytosis (LY), lymph node enlargement (LN) and splenomegaly (SM). The HEV-binding activity of the cells was the highest in Binet stage A patients and in patients with B-MLUS (p < 0.05 in B-MLUS versus B-CLL LY, LN, SM). Based on these findings it is suggested that B-CLL patients show not only a clinical and immunophenotypical heterogeneity, but a diverse function of adhesion molecules.

Ultrastructural localization of major hydatid fluid antigens in brood capsules and protoscoleces of Echinococcus granulosus of human origin

Monospecific rabbit antisera obtained through experimental immunization with previously purified proteins were used in the ultrastructural localization of two hydatid fluid antigens, in brood capsules and protoscoleces of Echinococcus granulosus of human origin. The antigen-antibody reaction was revealed by a colloidal gold based method. Reaction was evident in the connective region of the germinal membrane and in the parenchyma of the protoscoleces. Both antigen 5 and antigen B were located in the interstitial material between the parenchymal cells and precisely associated with disorganized areas. The brood capsule wall and the brood capsule contents, the tegument of the protoscoleces, the parenchymal cells, the muscle cells, the calcareous corpuscles and the hooks did not contain antigen 5 or antigen B. Label was not observed in the lumen of the collecting ducts or in the flame cells, although antigen 5 was evident in the periluminal cytoplasm. The origin of the antigens and their release are discussed.

Incubation chambers for the staining of ultrathin sections. An in situ technique especially suited for immunocytochemistry

The preparation and use of incubation chambers for staining of ultrathin sections is described. As an example the immunogold staining is given which can be carried out in these devices in a more simple manner than normally possible, and with good results as shown by electron microscopy.