Characterization of canine microglial cells isolated ex vivo

Characterization of microglia/macrophage phenotypes in the spinal cord following intervertebral disc herniation

Dogs frequently suffer from traumatic spinal cord injury (SCI). Most cases of SCI have a favorable prognosis but 40-50% of dogs with paraplegia and absence of nociception do not regain ambulatory abilities, eventually leading to euthanasia. Microglia and infiltrating macrophages play a crucial role in inflammatory process after SCI. However, little is known about microglia/macrophage phenotypes representing a potential target for future therapeutic strategies. In the present study, the microglia/macrophage phenotype was characterized by immunohistochemistry in the morphologically unaltered canine spinal cord (10 control dogs) and during acute and subacute SCI (1-4 and 5-10 days post injury, 9 and 8 dogs, respectively) using antibodies directed against IBA1, MAC387, MHC-II, lysozyme, EGR2, myeloperoxidase, CD18, CD204 and lectin from Griffonia simplicifolia (BS-1). The expression of these markers was also analyzed in the spleen as reference for the phenotype of histiocytic cells. Histological lesions were absent in controls. In acute SCI, 4 dogs showed mild to moderate hemorrhages, 2 dogs bilateral gray matter necrosis and 6 dogs mild multifocal axonal swellings and myelin sheath dilation. One dog with acute SCI did not show histological alterations except for few dilated myelin sheaths. In subacute SCI, variable numbers of gitter cells, axonal changes and dilated myelin sheaths were present in all dogs and large areas of tissue necrosis in 2 dogs. Neuronal chromatolysis was found in 3 dogs with acute and subacute SCI, respectively. In control dogs, microglia/macrophage constitutively expressed IBA1 and rarely other markers. In acute SCI, a similar marker expression was found except for an increase in MAC387-positive cells in the spinal cord white matter due to an infiltration of few blood-borne macrophages. In subacute SCI, increased numbers of microglia/macrophages expressed CD18, CD204 and MHC-II in the gray matter SCI indicating enhanced antigen recognition, processing and presentation as well as cell migration and phagocytosis during this stage. Interestingly, only CD204-positive cells were upregulated in the white matter, which might be related to gray-white matter heterogeneity of microglia as previously described in humans. The present findings contribute to the understanding of the immunological processes during SCI in a large animal model for human SCI.

Isolation of microglia from retinas of chronic ocular hypertensive rats

Microglia are the principal glial cells involved in the processes of immune inflammation within both retina and optic nerve, especially under the context of glaucomatous neuropathy. Considering the distinguishing role of retinal microglia in glaucoma and the lack of established protocol for microglia isolation from animal glaucoma model, the present study aimed to develop and validate a method with characteristics of both simplicity and efficiency for retinal microglia isolation from chronic ocular hypertensive (COH) rats. A Percoll gradient of various concentrations was used to separate microglia from whole retinal cells of the COH rats and control group. The finally isolated microglia were identified by CD11b and Iba-1 immunofluorescence staining, and the cell viability was determined by trypan blue staining. Additionally, the proportion of microglia in the whole retina cells was identified by flow cytometry. Results showed that the survival rates of isolated retinal microglia with the Percoll gradient method were 67.2 ± 4% and 67.6 ± 3% in control and COH groups, respectively. The proportion of the microglia population in the whole retinal cells was about 0.4–0.93%. To conclude, the present study confirmed that the application of Percoll gradient could effectively separate microglia from retinas of COH rats, which will probably enrich the tool kit for basic researchers of glaucoma specialty and help with scientific investigations.

Beneficial and detrimental impact of transplanted canine adipose-derived stem cells in a virus-induced demyelinating mouse model

In recent years stem cell therapies have been broadly applied in various disease models specifically immune mediated and degenerative diseases. Whether adipose-derived stem cells might represent a useful therapeutic option in virus-triggered central nervous system diseases has not been investigated so far. Theiler's murine encephalomyelitis (TME) and canine distemper encephalitis are established, virus-mediated animal models sharing many similarities with multiple sclerosis (MS). Canine adipose-derived stem cells (ASC) were selected since dogs might serve as an important translational model for further therapeutic applications. The aim of the present study was to investigate whether canine ASC influence clinical signs, axonal damage, demyelination and inflammation during TME. ASC were transplanted intravenously (iv) or intra-cerebroventricularly (icv) at 7 (early) or 42 (late) days post infection (dpi) in TME virus (TMEV) infected mice. TMEV/ASC iv animals transplanted at 7dpi displayed a transient clinical deterioration in rotarod performance compared to TMEV/control animals. Worsening of clinical signs was associated with significantly increased numbers of microglia/macrophages and demyelination in the spinal cord. In contrast, late transplantation had no influence on clinical findings of TMEV-infected animals. However, late TMEV/ASC iv transplanted animals showed reduced axonal damage compared to TMEV/control animals. Screening of spinal cord and peripheral organs for transplanted ASC revealed no positive cells. Surprisingly, iv transplanted animals showed pulmonary follicular aggregates consisting of T- and B-lymphocytes. Thus, our data suggest that following intravenous application, the lung as priming organ for lymphocytes seems to play a pivotal role in the pathogenesis of TME. Consequences of T-lymphocyte priming in the lung depend on the disease phase and may be responsible for disease modifying effects of ASC.

S100A8/A9 Drives Neuroinflammatory Priming and Protects against Anxiety-like Behavior after Sepsis

Sepsis commonly results in acute and chronic brain dysfunction, which dramatically increases the morbidity associated with this common disease. Chronic brain dysfunction in animal models of sepsis survival is linked to persistent neuroinflammation and expression of multiple cytokines. However, we have found previously that microglia predominantly upregulate the damage associated molecule S100A8/A9 after sepsis. In this article, we show that S100A8/A9 is increased in the brains of patients who died of sepsis and that S100A8 is expressed in astrocytes and myeloid cells. Using a mouse model of sepsis survival, we show that S100A8/A9 is persistently expressed in the brain after sepsis. S100A9 expression is necessary for recruitment of neutrophils to the brain and for priming production of reactive oxygen species and TNF-α secretion in microglia and macrophages. However, despite improving these indices of chronic inflammation, S100A9 deficiency results in worsened anxiety-like behavior 2 wk after sepsis. Taken together, these results indicate that S100A8/A9 contributes to several facets of neuroinflammation in sepsis survivor mice, including granulocyte recruitment and priming of microglial-reactive oxygen species and cytokine production, and that these processes may be protective against anxiety behavior in sepsis survivors.

Mesenchymal Stem Cells Form 3D Clusters Following Intraventricular Transplantation

Mesenchymal stem cells (MSCs) are regarded as an immune privileged cell type with numerous regeneration-promoting effects. The in vivo behavior of MSC and underlying mechanisms leading to their regenerative effects are largely unknown. The aims of this study were to comparatively investigate the in vivo behavior of canine (cMSC), human (hMSC), and murine MSC (mMSC) following intra-cerebroventricular transplantation. At 7 days post transplantation (dpt), clusters of cMSC, hMSC, and mMSC were detected within the ventricular system. At 49 dpt, cMSC-transplanted mice showed clusters mostly consisting of extracellular matrix lacking transplanted MSC. Similarly, hMSC-transplanted mice lacked MSC clusters at 49 dpt. Xenogeneic MSC transplantation was associated with a local T lymphocyte-dominated immune reaction at both time points. Interestingly, no associated inflammation was observed following syngeneic mMSC transplantation. In conclusion, transplanted MSC formed intraventricular cell clusters and exhibited a short life span in vivo. Xenogeneically in contrast to syngeneically transplanted MSC triggered a T cell-mediated graft rejection indicating that MSCs are not as immune privileged as previously assumed. However, MSC may mediate their effects by a "hit and run" mechanism and future studies will show whether syngeneically or xenogeneically transplanted MSCs exert better therapeutic effects in animals with CNS disease.

Morphologic, phenotypic, and transcriptomic characterization of classically and alternatively activated canine blood-derived macrophages in vitro

Macrophages are a heterogeneous cell population playing a pivotal role in tissue homeostasis and inflammation, and their phenotype strongly depends on the micromilieu. Despite its increasing importance as a translational animal model for human diseases, there is a considerable gap of knowledge with respect to macrophage polarization in dogs. The present study comprehensively investigated the morphologic, phenotypic, and transcriptomic characteristics of unstimulated (M0), M1- (GM-CSF, LPS, IFNγ-stimulated) and M2- (M-CSF, IL-4-stimulated)-polarized canine blood-derived macrophages in vitro. Scanning electron microscopy revealed distinct morphologies of polarized macrophages with formation of multinucleated cells in M2-macrophages, while immunofluorescence employing literature-based prototype-antibodies against CD16, CD32, iNOS, MHC class II (M1-markers), CD163, CD206, and arginase-1 (M2-markers) demonstrated that only CD206 was able to discriminate M2-macrophages from both other phenotypes, highlighting this molecule as a promising marker for canine M2-macrophages. Global microarray analysis revealed profound changes in the transcriptome of polarized canine macrophages. Functional analysis pointed out that M1-polarization was associated with biological processes such as "respiratory burst", whereas M2-polarization was associated with processes such as "mitosis". Literature-based marker gene selection revealed only minor overlaps in the gene sets of the dog compared to prototype markers of murine and human macrophages. Biomarker selection using supervised clustering suggested latexin (LXN) and membrane-spanning 4-domains, subfamily A, member 2 (MS4A2) to be the most powerful predicting biomarkers for canine M1- and M2-macrophages, respectively. Immunofluorescence for both markers demonstrated expression of both proteins by macrophages in vitro but failed to reveal differences between canine M1 and M2-macrophages. The present study provides a solid basis for future studies upon the role of macrophage polarization in spontaneous diseases of the dog, a species that has emerging importance for translational research.

Canine Macrophage DH82 Cell Line As a Model to Study Susceptibility to Trypanosoma cruzi Infection

Trypanosoma cruzi is an obligatory intracellular protozoan parasite, and it is the etiological agent of Chagas' disease that is endemic in the Americas. In addition to humans, a wide spectrum of mammals can be infected by T. cruzi, including dogs. Dogs develop acute and chronic disease, similar to human infection. T. cruzi can infect almost all cell types and after cell invasion, the metacyclics trypomastigotes localize in the cytoplasm, where they transform into amastigotes, the replicative form of T. cruzi in mammals. After amastigote multiplication and differentiation, parasites lyse host cells and spread through the body by blood circulation. In this work, we evaluated the in vitro ability of T. cruzi to infect a canine macrophage cell line DH82 compared with RAW264.7, a murine tissue culture macrophage. Our results have shown that the T. cruzi is able to infect, replicate and differentiate in DH82 cell line. We observed that following treatment with LPS and IFN-γ DH82 cells were more resistant to infection and that resistance was not related reactive oxygen species production in our system. In this study, we also found that DH82 cells became more susceptible to T. cruzi infection when cocultured with apoptotic cells. The analysis of cytokine production has showed elevated levels of the TGF-β, IL-10, and TNF-α produced by T. cruzi-infected canine macrophages. Additionally, we demonstrated a reduced expression of the MHC class II and CD80 by infected DH82 cell line.

Immunophenotyping of immune cell populations in the raccoon (Procyon lotor)

The raccoon (Procyon lotor) is a highly adaptable carnivore that has rapidly conquered Europe over the last decades and represents a potential candidate as pathogen reservoir, bearing the risk for transmission of infectious agents, as zoonosis or spill-over, to other wild life and domestic animals and man. Comprehensive investigations of infectious diseases in raccoons require a detailed knowledge of the participating immune cell populations. To close this gap of knowledge, various antibodies were tested for cross-reactivity with leukocytes in lymphoid organs and peripheral blood of raccoons using immunohistochemistry and flow cytometry, respectively. Eight out of 16 antibodies, directed against CD3, CD79α, Pax-5, IgG, CD44, MHC class II, myeloid/histiocyte antigen (MAC387), and Iba-1 exhibited a specific immunoreaction with cells in distinct anatomical compartments in formalin-fixed paraffin-embedded lymphoid tissues. Flow cytometric analysis revealed that 7 out of 18 antibodies directed against CD11c, CD14, CD21, CD44, CD79α, MHC class I and II cross-reacted with peripheral blood-derived raccoon leukocytes. Summarized, the usefulness of several cross-reacting antibodies was determined for the characterization of raccoon immune cells in immunohistochemistry and flow cytometry, offering the opportunity to study the raccoon immune system under normal and diseased conditions.

Microglial ROS production in an electrical rat post-status epilepticus model of epileptogenesis

Reactive oxygen species and inflammatory signaling have been identified as pivotal pathophysiological factors contributing to epileptogenesis. Considering the development of combined anti-inflammatory and antioxidant treatment strategies with antiepileptogenic potential, a characterization of the time course of microglial reactive oxygen species generation during epileptogenesis is of major interest. Thus, we isolated microglia cells and analyzed the generation of reactive oxygen species by flow cytometric analysis in an electrical rat post-status epilepticus model. Two days post status epilepticus, a large-sized cell cluster exhibited a pronounced response with excessive production of reactive oxygen species upon stimulation with phorbol-myristate-acetate. Neither in the latency phase nor in the chronic phase with spontaneous seizures a comparable cell population with induction of reactive oxygen species was identified. We were able to demonstrate in the electrical rat post-status-epilepticus model, that microglial ROS generation reaches a peak after the initial insult, is only marginally increased in the latency phase, and returns to control levels during the chronic epileptic phase. The data suggest that a combination of anti-inflammatory and radical scavenging approaches might only be beneficial during a short time window after an epileptogenic brain insult.

Passage-dependent morphological and phenotypical changes of a canine histiocytic sarcoma cell line (DH82 cells)

DH82 cells represent a permanent macrophage cell line isolated from a dog with histiocytic sarcoma (HS) and are commonly used in various fields of research upon infection and cancer, respectively. Despite its frequent use, data on cell surface antigen expression of this cell line are fragmentary and in part inconsistent. We therefore aimed at a detailed morphological and antigenic characterization of DH82 cells with respect to passage-dependent differences. Cellular morphology of early (≤ 13) and late (≥ 66) passages of DH82 cells was evaluated via scanning electron microscopy. Moreover, cells were labelled with 10 monoclonal antibodies directed against CD11c, CD14, CD18, CD44, CD45, CD80, CD86, MHC-I, MHC-II, and ICAM-1 for flow cytometric analysis. Early passage cells were characterized by round cell bodies with abundant small cytoplasmic projections whereas later passages exhibited a spindle-shaped morphology with large processes. The percentage of CD11c-, CD14-, CD18-, CD45-, and CD80 positive cells significantly decreased in late passages whereas the expression of CD44, CD86, MHC-I, MHC-II and ICAM-1 remained unchanged. DH82 cells represent a remarkably heterogeneous cell line with divergent antigenic and morphologic properties. The present findings have important implications for future studies, which should consider distinct characteristics with regard to the used passage.

Isolation and ex vivo characterization of the immunophenotype and function of microglia/macrophage populations in normal dog retina

Microglia are the primary resident immune cells of the retina and are involved in the pathogenesis of various retinal diseases. In this study, we optimized experimental conditions to isolate microglia from canine retinas and characterized ex vivo their immunophenotype and function using flow cytometry (FACS). The most suitable protocol included a mechanical dissociation of the retina and an enzymatic digestion using DNAse and collagenase. Extraction was carried out by density gradient centrifugation, and retinal microglia accumulated on distinct interfaces of 1.072 and 1.088 g/mL of a Percoll gradient. Immunophenotypical characterization was performed with monoclonal antibodies CD11b, CD11c, CD18, CD45, CD44, B7-1 (CD80), B7-2 (CD86), CD1c, ICAM-1 (CD54), CD14, MHCI, MHCII, CD68, CD3, CD4, CD8α, and CD21. The most prevalent microglia population in the normal canine retina is CD11b(high)CD45(low). Functionally, retinal microglia exhibited phagocytosis and reactive oxygen species (ROS) generation activities. To conclude, ex vivo examinations of retinal microglia are feasible and possibly reflect the in vivo conditions, avoiding artifacts observed in tissue culture. The established method will be relevant to examine microglia from diseased canine retinas in order to elucidate their roles in degenerative processes.

Impact of Theiler's virus infection on hippocampal neuronal progenitor cells: differential effects in two mouse strains

AIMS

Disease-associated alterations in hippocampal neurogenesis are discussed as an important factor contributing to long-term consequences of central nervous system diseases. Therefore, the study aimed to determine the impact of Theiler's murine encephalomyelitis virus infection on hippocampal cell proliferation, neuronal progenitor cells and neurogenesis as well as the influence of microglia on respective disease-associated alterations.

METHODS

The impact of the infection was evaluated in two mouse strains which differ in the disease course, with an acute polioencephalitis followed by virus elimination in C57BL/6 mice and a chronic demyelinating disease in SJL/J mice.

RESULTS

Infection with the low neurovirulent BeAn strain did not exert significant acute effects regardless of the mouse strain. In the chronic phase, the number of neuronal progenitor cells and early postmitotic neurones was significantly reduced in infected SJL/J mice, whereas no long-term alterations were observed in C57BL/6 mice. A contrasting course of microglia activation was observed in the two mouse strains, with an early increase in the number of activated microglia cells in SJL/J mice and a delayed increase in C57BL/6 mice. Quantitative analysis did not confirm a correlation between the number of activated microglia and the number of neuronal progenitor cells and early postmitotic neurones. However, flow cytometric analyses revealed alterations in the functional state of microglial cells which might have affected the generation of neuronal progenitor cells.

CONCLUSIONS

Theiler's murine encephalomyelitis virus infection can exert delayed effects on the hippocampal neuronal progenitor population with long-term alterations evident 3 months following infection. These alterations proved to depend on strain susceptibility and might contribute to detrimental consequences of virus encephalitis such as cognitive impairment.

Miglustat improves purkinje cell survival and alters microglial phenotype in feline Niemann-Pick disease type C

Niemann-Pick disease type C (NPC disease) is an incurable cellular lipid-trafficking disorder characterized by neurodegeneration and intralysosomal accumulation of cholesterol and glycosphingolipids. Treatment with miglustat, a small imino sugar that reversibly inhibits glucosylceramide synthase, which is necessary for glycosphingolipid synthesis, has been shown to benefit patients with NPC disease. The mechanism(s) and extent of brain cellular changes underlying this benefit are not understood. To investigate the basis of the efficacy of miglustat, cats with disease homologous to the juvenile-onset form of human NPC disease received daily miglustat orally beginning at 3 weeks of age. The plasma half-life of miglustat was 6.6 ± 1.1 hours, with a tmax, Cmax, and area under the plasma concentration-time curve of 1.7 ± 0.6 hours, 20.3 ± 4.6 μg/mL, and 104.1 ± 16.6 μg hours/mL, respectively. Miglustat delayed the onset of neurological signs and increased the lifespan of treated cats and was associated with decreased GM2 ganglioside accumulation in the cerebellum and improved Purkinje cell survival. Ex vivo examination of microglia from the brains of treated cats revealed normalization of CD1c and class II major histocompatibility complex expression, as well as generation of reactive oxygen species. Together, these results suggest that prolonged Purkinje cell survival, reduced glycosphingolipid accumulation, and/or the modulation of microglial immunophenotype and function contribute to miglustat-induced neurological improvement in treated cats.

The role of pro- and anti-inflammatory cytokines in the pathogenesis of spontaneous canine CNS diseases

Dogs are comparatively frequently affected by various spontaneously occurring inflammatory and degenerative central nervous system (CNS) conditions, and immunopathological processes are a hallmark of the associated neuropathology. Due to the low regenerative capacity of the CNS a sophisticated understanding of the underlying molecular basis for disease initiation, progression and remission in canine CNS diseases represents a prerequisite for the development of novel therapeutical approaches. In addition, as many spontaneous canine CNS diseases share striking similarities with their human counterpart, knowledge about the immune pathogenesis may in part be translated for a better understanding of certain human diseases. In addition to cytokine-driven differentiation of peripheral leukocytes including different subsets of T cells recent research suggests a pivotal role of these mediators also in phenotype polarization of resident glial cells. Cytokines thus represent the key mediators of the local and systemic immune response in CNS diseases and their orchestration significantly decides on either lesion progression or remission. The aim of the present review is to summarize the growing number of data focusing on the molecular basis of the immune response during spontaneous canine CNS diseases and to detail the effect of cytokines on the immune pathogenesis of selected idiopathic, infectious, and traumatic canine CNS diseases. Steroid-responsive meningitis arteritis (SRMA) represents a unique idiopathic disease of leptomeningeal blood vessels characterized by excessive IgA secretion into the cerebrospinal fluid. Recent reports have given sophisticated insights into the cytokine-driven, immune-mediated pathogenesis of SRMA that is characterized by a biased T helper 2 cell response. Canine distemper associated leukoencephalitis represents an important spontaneously occurring disease that allows investigations on the basic pathogenesis of immune-mediated myelin loss. It is characterized by an early virus-induced up-regulation of pro-inflammatory cytokines with chronic bystander immune-mediated demyelinating processes. Lastly, canine spinal cord injury (SCI) shares many similarities with the human counterpart and most commonly results from intervertebral disk disease. The knowledge of its pathogenesis is largely restricted to experimental studies in rodents, and the impact of immune processes that accompany secondary injury is discussed controversially. Recent investigations on canine SCI highlight the pivotal role of pro-inflammatory cytokine expression that is paralleled by a dominating reaction of microglia/macrophages potentially indicating a polarization of these immune cells into a neurotoxic and harmful phenotype. This report will review the role of cytokines in the immune processes of the mentioned representative canine CNS diseases and highlight the importance of cytokine/cytokine interaction as a useful therapeutic target in canine CNS diseases.

Characterization of Immune Cell Infiltration Into Canine Intracranial Meningiomas

Meningiomas are the most common intracranial tumors in dogs. A variety of inflammatory cells have been shown to invade these tumors in people, but little is known about interactions between the immune system and naturally occurring brain tumors in dogs. The purpose of this study was to investigate the presence of a variety of immune cell subsets within canine intracranial meningiomas. Twenty-three formalin-fixed, paraffin-embedded tumor samples were evaluated using immunohistochemistry with antibodies specific for CD3, CD79a, CD18, CD11d (αD), CD45RA, forkhead box P3, and Toll-like receptors 4 and 9. Immune cell infiltration was evident in all samples, with a predominance of CD3+ T cells. Large numbers of CD18+ microglia and macrophages were noted surrounding and infiltrating the tumors, and a subset of these cells within the tumor appeared to be CD11d+. Scattered macrophages at the tumor–brain interface were TLR4+ and TLR9+. Rare CD79a+ B cells were noted in only a small subset of tumors. Lesser numbers of lymphocytes that were CD11d+, CD45RA+, or FoxP3+ were noted in a number of the meningiomas. Although the function of these cells is not yet clear, work in other species suggests that evaluation of this immune cell infiltrate may provide important prognostic information and may be useful in the design of novel therapies.

Regional topographical differences of canine microglial immunophenotype and function in the healthy spinal cord

Differences in the regulation of surface molecule expression and functional activity of microglia, the resident immune effector elements of the central nervous system (CNS), might give important insights into understanding the predilection sites of some diseases within the CNS. Therefore, canine microglial cells in relation to different topographical regions within the healthy CNS were evaluated ex vivo from the brain, cervical, and thoracolumbar spinal cord using density gradient centrifugation and flow cytometry in a homogenous dog population. Immunophenotypical characterization showed physiological regional differences for B7-1, CD14, CD44, CD1c, CD18, CD11b, and CD11c. Both, phagocytosis and ROS generation revealed differences between the brain, cervical, and thoracolumbar spinal cord. Our results emphasize that microglia displays physiological topographical regional differences within the CNS. The dog seems to be an ideal model to further investigate the role of microglia in focal pathological conditions of the spinal cord.

MHC class II expression by beta2 integrin (CD18)-positive microglia, macrophages and macrophage-like cells in rabbit retina

The aim of this study was to investigate the developmental expression of major histocompatibility complex class II (MHCII) by microglia and macrophages and their relationship to blood vessels in the retina, a representative tissue of the central nervous system. Such information is crucial to understanding the role of these cells in immune surveillance. Wholemount preparations of retinas from late embryonic, postnatal and adult rabbits were subjected to three-colour fluorescence microscopy using beta2 integrin (CD18) and MHCII antibodies and biotinylated Griffonia simplicifolia B4 isolectin labelling of blood vessels. CD18+ cells consistently exhibited characteristics of macrophages or microglia in the vascularized and non-vascularized regions of the retina, respectively. At all ages, MHCII was expressed by a high proportion of cells in the vascularized region, which contained macrophage-like 'parenchymal cells' as well as typical perivascular macrophages. MHCII expression by ramified microglia, first detected on postnatal day 30, was lower in the peripheral retina and intermediate in the avascular region of the myelinated streak. The observed localization of MHCII+ cells in relation to blood vessels and location-dependent differences in MHCII expression point to the possibility that these cells may be distributed strategically within the retina to provide multiple lines of defence against immune challenge arriving via the retinal vasculature.

Differential expression of CD45 on canine microglial cells

CD45, also called leucocyte common antigen is a transmembrane protein tyrosine phosphatase on the surface of nearly all white blood cells and has a functional role in signal transduction. In the brain, the expression of CD45 can be used to distinguish microglial cells with a characteristic phenotype of CD11b/c+ and CD45(low) from other central nervous system (CNS) macrophages which show an expression of CD11b/c+ and CD45(high). In the course of pathological changes in the CNS, microglia in rodents is known to readily upregulate expression of various surface molecules, such as CD45. Understanding the mechanisms that regulate expression of surface molecules is essential to study the pathogenesis of CNS diseases. In the present study, the expression of CD45 on microglia of 42 dogs was examined ex vivo by means of flow cytometry. The dogs were classified in two groups according to the histopathological diagnosis in the CNS. All dogs without changes in the CNS (group I; n = 22) only showed low percentages of CD45+ microglial cells. In group II consisting of 20 dogs with different intracranial diseases varying results were obtained. Thirteen dogs showed a low percentage of CD45+ microglial cells whereas seven dogs exhibited high percentages of microglial cells expressing CD45. Evaluation of expression intensity in these seven dogs revealed two subpopulations of CD45+ microglial cells: a large subpopulation with CD45(low) and a small subpopulation with CD45(high). The expression intensity of CD45(high) was comparable with that of canine monocytes. It was attempted to correlate these findings to age of the animals, underlying disease, duration of clinical signs, medical treatment, occurrence of seizure activity and the expression of other surface molecules. It appeared that dogs with high percentages of CD45+ suffered from long-lasting CNS disease with seizures. In future studies, the reason and consequences for upregulated CD45 in long-lasting CNS diseases has to be further evaluated.

Optimized isolation enables ex vivo analysis of microglia from various central nervous system regions

Ex vivo analysis is an accurate and convenient way to study in vivo microglia phenotype and function. However, current microglia isolation protocols for ex vivo analysis show many differences in isolation steps (perfusion, removal of meninges and blood vessels, mechanical dissociation, enzymatic dissociation, density separation, immunomagnetic separation, and fluorescence-activated cell sorting), often without addressing their effects on microglia purity, number, phenotype, and function. Therefore, the aim of this study was to provide an optimized isolation protocol with emphasis on microglia purity and number to enable ex vivo analysis of adult mouse microglia. The application of this protocol for ex vivo phenotype and functional analysis is corroborated by results from flow cytometry, gene expression analysis, chemotaxis, and phagocytosis assays. In addition, this study shows the possibility to analyze microglia isolated from various central nervous system regions such as optic nerve, striatum, hippocampus, spinal cord, cerebellum, and cerebral cortex. Furthermore, this is the first study presenting DRAQ5 as a superior alternative to propidium iodide for the discrimination between living and dead cells. DRAQ5 staining facilitated the identification of microglia upon flow cytometry without the need of additional fluorescent markers. Along with a favorable emission spectrum, DRAQ5 proved a valuable tool for flow cytometry of microglia. The presented optimized microglia isolation protocol for ex vivo analysis offers the opportunity to obtain more insight into both general and region-specific microglia behavior.

Enhanced brain targeting efficiency of intranasally administered plasmid DNA: an alternative route for brain gene therapy

Recently, nasal administration has been studied as a noninvasive route for delivery of plasmid DNA encoding therapeutic or antigenic genes. Here, we examined the brain targeting efficiency and transport pathways of intranasally administered plasmid DNA. Quantitative polymerase chain reaction (PCR) measurements of plasmid DNA in blood and brain tissues revealed that intranasally administered pCMVbeta (7.2 kb) and pN2/CMVbeta (14.1 kb) showed systemic absorption and brain distribution. Following intranasal administration, the beta-galactosidase protein encoded by these plasmids was significantly expressed in brain tissues. Kinetic studies showed that intranasally administered plasmid DNA reached the brain with a 2,595-fold higher efficiency than intravenously administered plasmid DNA did, 10 min post-dose. Over 1 h post-dose, the brain targeting efficiencies were consistently higher for intranasally administered plasmid DNA than for intravenously administered DNA. To examine how plasmid DNA enters the brain and moves to the various regions, we examined tissues from nine brain regions, at 5 and 10 min after intranasal or intravenous administration of plasmid DNA. Intravenously administered plasmid DNA displayed similar levels of plasmid DNA in the nine different regions, whereas, intranasally administered plasmid DNA exhibited different levels of distribution among the regions, with the highest plasmid DNA levels in the olfactory bulb. Moreover, plasmid DNA was mainly detected in the endothelial cells, but not in glial cells. Our results suggest that intranasally applied plasmid DNA may reach the brain through a direct route, possibly via the olfactory bulb, and that the nasal route might be an alternative method for efficiently delivering plasmid DNA to the brain.

Optimization of conditions for in vitro production of radical oxygen species and expression of tissue factor by canine mononuclear cells and granulocytes for use in high-throughput assays

The purpose of this study was to optimize conditions for high throughput measurement of radical oxygen species (ROS) production and expression of tissue factor, also termed procoagulant activity, by canine leukocytes. Granulocytes and mononuclear cells were separated by density gradient centrifugation from peripheral blood collected on several occasions from three healthy large breed dogs. To determine optimal conditions for ROS production, granulocytes were incubated for 1 or 3h in PBG (PBS containing 0.5% BSA and 5mM glucose) or RPMI containing 10% fetal bovine serum (FBS); lipopolysaccharide (LPS), zymosan, peptidoglycan (PGN) and phorbol myristate acetate (PMA) were used as stimuli. ROS was assessed by conversion of the nonfluorescent dye dihydrorhodamine 123 to fluorescent rhodamine 123 by radical species released into the media. To identify optimal conditions for expression of tissue factor, mononuclear cells were incubated for 5h in RPMI containing different concentrations of heat-inactivated FBS (HI-FBS), and LPS, zymosan, PGN or PMA as stimuli. Expression of tissue factor was determined using a one-stage recalcification assay performed in an automated nephelometric coagulation analyzer. Neither LPS nor zymosan increased ROS production by granulocytes incubated in PBG media. In contrast, granulocytes incubated in RPMI had dose-dependent increases in ROS production in response to zymosan and PGN. ROS production was significantly increased by incubation with concentrations of LPS of 0.01microg/ml or greater, and by zymosan concentrations of 0.1microg/ml or greater. ROS production in response to incubation with PMA was significantly increased starting at 10(-7)M, and was significantly greater for cells incubated in RPMI than cells incubated in PBG. LPS-, zymosan- and PGN-stimulated procoagulant activity increased in a dose-dependent manner, whereas PMA-stimulated procoagulant activity peaked at 10(-7)M. Increasing concentrations of HI-FBS significantly increased LPS-, zymosan- and PGN-induced procoagulant activity of mononuclear cells. Results obtained in this study indicate production of ROS by canine granulocytes is optimal when these cells are incubated for 3h in RPMI with LPS (0.1microg/ml), zymosan (10 microg/ml), PGN (10 microg/ml), and PMA (10(-7)M). Furthermore, canine mononuclear cells express procoagulant activity in response to LPS, zymosan, PGN, and PMA, and responses to LPS, zymosan and PGN are enhanced by the addition of HI-FBS. These findings suggest that HI-FBS retains important serum proteins that facilitate interactions between each of these bacterial or yeast derived products and the mononuclear cells. Consequently, future studies regarding the regulation of procoagulant activity by canine mononuclear cells should be performed in the presence of HI-FBS. Both assays utilized in this study allow high throughput of samples, and therefore are appropriate choices for rapid screening of conditions and/or therapeutic interventions affecting the canine inflammatory system.

Canine microglial cells: stereotypy in immunophenotype and specificity in function?

Microglial cells represent the endogenous immune system of the central nervous system (CNS). Upon pathological insults they reveal their immunological potential aimed at regaining homeostasis. These reactions have long been believed to follow a uniform and unspecific pattern which is irrespective to the underlying disease entity. Evidence is growing that this view seriously underrates microglial competence as the defenders of the CNS. In the present study, microglial cells of 47 dogs were examined ex vivo by means of flow cytometry. Ex vivo examination included immunophenotypic characterization using eight different surface markers and functional studies such as phagocytosis assay and the reactive oxygen species (ROS) generation test. The dogs were classified according to their histopathological diagnoses in disease categories (controls, canine distemper virus (CDV) induced demyelination, other diseases of the CNS) and results of microglial reaction profiles were compared. Immunophenotypic characterization generally revealed relative high conformity in the microglial disease response among the different groups, however the functional response was shown to be more specific. Dogs with intracranial inflammation and dogs with demyelination showed an enhanced phagocytosis, whereas a significant up-regulation of ROS generation was found in dogs with demyelination due to CDV infection. This strongly suggests a specific response of microglia to infection with CDV in the settings of our study and underlines the pivotal role of microglial ROS generation in the pathogenesis of demyelinating diseases, such as canine distemper.

Microglial cell activation in demyelinating canine distemper lesions

Microglia cells are the principal immune effector elements of the brain responding to any pathological event. To elucidate the possible role of microglia in initial non-inflammatory demyelination in canine distemper virus (CDV) infection, microglia from experimentally CDV infected dogs were isolated ex vivo by density gradient centrifugation and characterized immunophenotypically and functionally using flow cytometry. Results from dogs with demyelinating lesions were compared to results from recovered dogs and two healthy controls. CDV antigen could be detected in microglia of dogs with histopathologically confirmed demyelination. Microglia of these dogs showed marked upregulation of the surface molecules CD18, CD11b, CD11c, CD1c, MHC class I and MHC class II and a tendency for increased expression intensity of ICAM-1 (CD54), B7-1 (CD80), B7-2 (CD86), whereas no increased expression was found for CD44 and CD45. Functionally, microglia exhibited distinctly enhanced phagocytosis and generation of reactive oxygen species (ROS). It was concluded that in CDV infection, there is a clear association between microglial activation and demyelination. This strongly suggests that microglia contribute to acute myelin destruction in distemper.