First published online August 30, 2007
Stem Cells
Vol. 25 No.
12
December 2007, pp.
3165
-3172
doi:10.1634/stemcells.2007-0508; www.StemCells.com
© 2007 AlphaMed Press
TISSUE-SPECIFIC STEM CELLS |
Irradiation Does Not Compromise or Exacerbate the Innate Immune Response in the Brains of Mice That Were Transplanted with Bone Marrow Stem Cells
Nicolas P. Turrin,
Marie-Michèle Plante,
Martine Lessard,
Serge Rivest
Laboratory of Molecular Endocrinology, Centre Hospitalier de l'Université Laval Research Center, Department of Anatomy and Physiology, Laval University, Quebec City, Quebec, Canada
Key Words. Chimeric mice • Neuroinflammation • Microglia • Macrophages • Irradiation • Green fluorescent protein
Correspondence: Serge Rivest, Ph.D., Centre Hospitalier de l'Université Laval Research Center, Laboratory of Molecular Endocrinology, Department of Anatomy and Physiology, Laval University, 2705 Laurier Boulevard, Quebec City, Quebec, Canada, G1V 4G2. Telephone: (418) 654-2296; Fax: (418) 654-2761; e-mail: Serge.Rivest{at}crchul.ulaval.ca
Received on June 27, 2007;
accepted for publication on August 21, 2007.
First published online in STEM CELLS EXPRESS August 30, 2007.
 |
ABSTRACT
|
|---|
Microglia and invading macrophages play key roles in the brain immune response. The contributions of these two populations of cells in health and diseases have yet to be clearly established. The use of chimeric mice receiving bone marrow-derived stem cell grafts from green fluorescent protein (GFP)-expressing mice has provided an invaluable tool to distinguish between local and blood-derived monocytic populations. The validity of the method is questioned because of the possible immune alterations caused by the irradiation of the recipient mouse. In this experiment, we compared the brain expression of innate immune markers Toll-like receptor 2, interleukin-1β, tumor necrosis factor-
, and monocyte chemoattractant protein-1 in C57BL/6, GFP, and chimeric mice following an intracerebral injection of lipopolysaccharide. The endotoxin caused a marked transcriptional activation of all these innate immune genes in microglial cells across the ipsilateral side of injection. The expression patterns and signal intensity were similar in the brains of the three groups of mice. Consequently, the chimera technique is appropriate to study the role of infiltrating and resident immune cells in the brain without having immune compromised hosts.
Disclosure of potential conflicts of interest is found at the end of this article.
|
INTRODUCTION
|
|---|
Microglia are the resident immune cells of the brain and the principal effectors of the cerebral inflammatory response. Although the immune system of the central nervous system (CNS) was first thought to be isolated from the peripheral immune system, it was often suggested that the peripheral immune system could assist the CNS to fight off infection and disease [1]. Accumulating evidence supports the concept that progenitors in the bone marrow can differentiate into highly efficient macrophages/microglia in the intact brain [2, 3], although this process is strongly increased during acute injuries and chronic neurodegenerative diseases [4, 5]. Because invading macrophages and microglia are histologically and phenotypically very similar, an in vivo procedure was needed to study the difference between the two populations. Thus, mice were irradiated to kill all peripheral immune cells and subsequently grafted with bone marrow progenitors from green fluorescent protein (GFP)-expressing mice to visualize and tease out the respective roles of the graft-derived and resident cell populations [6]. This commonly used method has led to a flurry of discoveries that began to characterize the roles of the resident microglia versus invading macrophages [5, 7–9]. Furthermore, the chimera model opens the door to new powerful gene therapies to treat elusive CNS diseases such as Alzheimer disease (AD) [10].
However, the GFP chimeric mouse model is not without its criticisms. Concerns were raised in regard to possible CNS effect of radiation on the integrity of the blood-brain barrier (BBB) [11], blood vessels, and oligodendrocytes [12]. Other detrimental CNS effects of radiation could include microgliosis [13] and neural dysfunctions [14]. Irradiation was also found to increase proinflammatory signaling and cytokine gene expression in the CNS [12]. Taken together, these changes could be associated with an altered immune response in the brain following the creation of the chimera. If irradiation and the bone marrow transplant cause alterations of the innate immune response in the CNS, they could obfuscate the individual contribution of the infiltrating GFP progenitors and resident microglia. Such a phenomenon could severely compromise the interpretation of results using this approach.
Due to the importance of chimeric mice in the current research, it is critical to determine whether irradiation and transplant processes alter the immune properties of microglia. We used in situ hybridization to evaluate the expression of the gene encoding Toll-like receptor 2 (TLR2, a reliable marker of microglial activation [15]), tumor necrosis factor alpha (TNF-), and interleukin 1 beta (IL-1β) (proinflammatory cytokines) as well as monocyte chemoattractant protein (MCP-1, a chemokine involved in the recruitment of immune cells) in the brains of chimeric, C57BL/6 (recipient), and GFP-expressing (donor) mice following an immune challenge in the CNS. Intracerebral lipopolysaccharide (LPS) administration caused a robust expression of all immune markers in the ipsilateral side. The distribution pattern and signal intensity of the markers were identical in the brains of chimeric mice compared with the other groups of mice. These results indicate that the innate immune response is not compromised in the brains of chimeric mice that were transplanted with bone marrow stem cells and validate the use of such an approach to study the role of blood-derived microglia in health and diseases.
|
MATERIALS AND METHODS
|
|---|
C57BL/6 and Green Fluorescent Protein-Expressing Mice
Adult male (25–35 g) hemizygous transgenic mice expressing GFP under the control of the chicken β-actin promoter and the cytomegalovirus enhancer from an in-house maintained colony were used. These mice were originally purchased from the Jackson Laboratory (Bar Harbor, ME, http://www.jax.org) and crossbred into a C57BL/6 background for at least six generations. Age and sex-matched C57BL/6 mice were used for this experiment as controls. All animals were acclimated to standard laboratory conditions (14-hour light and 10-hour dark cycle; lights on at 06:00 and off at 20:00 hours) with free access to rodent chow and water. GFP mice were used as cell donors at 12–14 months of age. All protocols were conducted according to the Canadian Council on Animal Care guidelines as administered by the Laval University Animal Welfare Committee.
Irradiation and Bone Marrow Transplantation
A group (n = 10) of 2-month-old C57BL/6 mice (chimera group) was exposed to 10 gray total-body irradiation using a cobalt-60 source (Theratron-780 model; MDS Nordion, Ottawa, http://www.mds.nordion.com). A few hours later, the animals were injected via a tail vein with 17 x 106 bone marrow cells freshly collected from GFP mice. The cells were aseptically harvested by flushing femurs with Dulbecco's phosphate-buffered saline (DPBS) containing 2% fetal bovine serum. The samples were combined, filtered through a 40-µm nylon mesh and centrifuged. Recovered cells were resuspended in DPBS at a concentration of 17 x 106 viable nucleated cells per 200 microliters. Irradiated mice transplanted with this suspension were housed in autoclaved cages and treated with antibiotics (0.2 mg trimethoprim and 1 mg sulfamethoxazole/ml of drinking water given for 7 days before and 2 weeks after irradiation). Chimerism was confirmed by fluorescent-activated cell sorting (FACS) on red blood cell-lysed blood. Briefly, whole blood was taken from the facial vein and quickly suspended, and cells were washed multiple times in DPBS + 2% goat serum. Phycoerythrin (PE)-conjugated CD11b antibody was then added, and cells were washed again in DPBS + 5% goat serum. Red blood cells were lysed with hemolysin according to manufacturer's protocol (Beckman Coulter, Fullerton, CA, http://www.beckmancoulter.com), and cells were washed with DPBS and resuspended in equal volumes of DPBS + 5% goat serum and 4% paraformaldehyde (pH 7.6). The cells were analyzed using a two-laser, four-color FACSCalibur flow cytometer and CellQuest Pro software (BD Biosciences, San Diego, http://www.bdbiosciences.com) then sorted according to PE-CD11b and GFP fluorescence. Animals were used 2 months after transplantation.
Intracerebral Injections
The mice were anesthetized with isoflurane, and the site of injection was stereotaxically reached (David Kopf Instruments, Tujunga, CA, http://www.kopfinstruments.com). For the acute intrastriatal injections, the coordinates from the bregma were 0 mm anteroposterior, –2 mm lateral, and –3 mm dorsoventral. One microliter of solution containing either 0.9% NaCl (vehicle) or lipopolysaccharide (LPS 1.0 µg/µl; Sigma-Aldrich, St. Louis, http://www.sigmaaldrich.com) was delivered over a period of 2 minutes. The animals were then sacrificed at 6 or 24 hours postinjection. Please note that nonirradiated C57BL/6 mice were used for the vehicle group to show the localized signal in the region adjacent to the injection site. This is quite different from the LPS treatment that causes a robust and reliable inflammatory response in the CNS (see Results). This explains why only LPS-treated groups were used for the quantitative analyses of the innate immune reaction to the endotoxin.
To collect the brain tissues, the mice were deeply anesthetized via an i.p. injection of a mixture of ketamine hydrochloride and xylazine and then rapidly perfused transcardially with 0.9% saline followed by 4% paraformaldehyde/3.8% Borax in sodium phosphate buffer (pH 9 at 4°C). The brains were rapidly removed from the skulls, postfixed overnight, and placed in a solution containing 10% sucrose diluted in 4% paraformaldehyde/3.8% Borax buffer (pH 9) overnight at 4°C. The brains were mounted on a microtome (Reichert-Jung, Cambridge Instruments Company, Deerfield, IL, http://www.leica.com), frozen with dry ice, and cut into 25-µm coronal sections from the olfactory bulb to the end of the medulla. The slices were collected in a cold cryoprotectant solution (0.05 M sodium phosphate buffer, pH 7.3, 30% ethylene glycol, 20% glycerol) and stored at –20°C.
Immunohistochemistry
Free-floating sections (25-µm thick) were incubated for 30 minutes in potassium phosphate buffer solution (KPBS) containing 4% goat serum, 1% bovine serum albumin, and 0.4% Triton X-100. Using the same buffer solution, the sections were then incubated for 90 minutes in primary antibody (Ab) (polyclonal rabbit anti-ionized calcium-binding adapter molecule 1 (iba1), 1:3,000; Wako Chemical, Osaka, Japan, http://www.wako-chem.co.jp/english) at room temperature. The sections were then rinsed 4 times for 5 minutes in KPBS followed by a 90-minute incubation in fluorochrome-goat secondary Ab (anti-rabbit Alexa-594, 1:1,000; Molecular Probes, Eugene, OR, http://probes.invitrogen.com). Sections were then rinsed 4 times for 5 minutes in KPBS, mounted onto SuperFrost slides (Fisher Scientific International, Hampton, NH, http://www.fisherscientific.com), stained with 4,6-diamidino-2-phenylindole (2 x 10–4%; Molecular Probes), and coverslipped with antifade medium composed of 96 mM Tris-Hcl, pH 8.0, 24% glycerol, 9.6% polyvinyl alcohol, and 2.5% diazabicyclooctane (Sigma). Visualization of the slides was done using a C-80 Nikon microscope and super high-pressure mercury lamp (Nikon, Tokyo, http://www.nikon.com) fitted with a Retiga EXi Fast digital camera (QImaging, Burnaby, BC, Canada, http://www.qimaging.com) feeding to a Precision 660 workstation (Dell, North York, ON, http://www.dell.com). The images were then processed to enhance contrast and sharpness using Adobe Photoshop 7 (Adobe Systems, San Jose, CA, http://www.adobe.com) and were assembled using Adobe Illustrator (Adobe Systems).
In Situ Hybridization and Combination of Immunohistochemistry with In Situ Hybridization
In situ hybridization was performed on every 12th section of the brain starting from the end of the olfactory bulb to the end of the cortex using 35S-labeled cRNA probes as described previously [16–18]. Immunocytochemistry was combined with the in situ hybridization protocol to determine whether TLR2 was expressed in GFP-expressing cells and microglia in the group of chimeric mice. Immunocytochemistry against green fluorescent protein (labeling bone marrow-derived infiltrating cells) or anti-ionized calcium binding adapter molecule 1 (labeling macrophages and microglia) was followed by in situ hybridization (TLR2 mRNA) as described previously [19]. The expression of TLR4, the receptor for LPS, was also evaluated. Although there was a slight expression of TLR4 in the area adjacent to the injection site at 6 and 24 hours, the signal was weak in all samples and not quantifiable (supplemental online Fig. 1). As previously reported, this receptor is not upregulated by LPS in the CNS.
Data Analysis
The relative intensity of mRNA signals was measured on BioMax MR x-ray films (Kodak, Rochester, NY, http://www.kodak.com). Transmittance values (referred to in this study as O.D.) of positive hybridization signal were measured under a Northern Light desktop illuminator (Imaging Research, Ste-Catherines, ON, Canada, http://www.imagingresearch.com) using a Sony camera video system attached to a Micro-Nikkor 55-mm Vivitar extension tube set for a Nikon lens and coupled to a Dimension GX270 personal computer (Dell) and ImageJ software (version 1.23, W. Rasband; National Institutes of Health, Bethesda, MD). O.D. for each pixel was calculated using a known standard of intensity and distance measurements from a logarithmic specter adapted from BioImage Visage 110s (Millipore, Billerica, MA, http://www.millipore.com). Sections from experimental animals were digitized and subjected to densitometric analysis, yielding average O.D.s. The O.D. for each section was corrected for the average background signal from the contralateral side. To standardize the sampling procedure for each brain, three sections closest to the injection site were analyzed and averaged. The sections corresponded approximately to the bregma +0.38-mm, +0.02-mm, and –0.34-mm sections in the Paxinos and Franklin brain atlas [20].
Statistical Analysis
Data were compiled and the statistical analysis was performed using SPSS software (v.13.0; Chicago, http://www.spss.com). Between-group differences of mRNA expression density were analyzed using analysis of variance (ANOVA). Comparisons between means of main effects were conducted by Bonferroni corrected t tests. An alpha < .05 was considered significant.
|
RESULTS
|
|---|
Induction of Inflammatory Markers Following Intracerebral LPS Administration
TLR2 expression is indicative of microglial activation, whereas TNF- and IL-1β are effector cytokines in inflammatory processes, and MCP-1 (CCL2) is a chemokine involved in the recruitment of immune cells to injured/inflamed sites. Intracerebral LPS administration led to a sharp upregulation of TLR2, TNF-, IL-1β, and MCP-1 radiating out from the site of injection at time 6 hours (Fig. 1). The hybridization signals were still present 24 hours following the treatment with LPS, although they were much more diffuse. The injection of vehicle saline solution caused expression of these markers only in regions adjacent to the cannula's tract.
View larger version (75K):
[in this window]
[in a new window]
|
Figure 1. Gene expression of inflammatory markers following intracerebral lipopolysaccharide injection. Photomicrographs of x-ray films from in situ hybridization signals for TLR2, TNF-, IL-1β, and MCP-1 mRNA in the brains of mice having received intraparenchymal LPS versus Veh and sacrificed 6 and 24 hours postinjection. Note the expression of the markers radiating out from the injection site at 6 and 24 hours. The top left panel shows the location of the injection in the dorsal basal ganglia. Abbreviations: h, hours; IL-1β, interleukin-1β; LPS, lipopolysaccharide; MCP-1, monocyte chemoattractant protein-1; TLR2, Toll-like receptor 2; TNF-, tumor necrosis factor ; Veh, vehicle.
|
|
Presence of GFP Bone Marrow-Derived Myeloid Cells in Chimeric Mice Following Intracerebral LPS Administration
Figure 2 illustrates how bone marrow-derived cells can be visualized in the brain of irradiated C57BL/6 mice having received bone marrow stem cell transplantations from GFP mice. The grafts rescue irradiated mice and provide a high level of chimerism (approximately 95%; Fig. 2A). At time 1 day after LPS administration, GFP+ cells were found in the CNS of chimeric mice, especially close to blood vessels (Fig. 2B). This phenomenon cannot be appreciated in nonchimeric C57BL/6 and GFP-expressing mice because most infiltrating cells have a microglial phenotype (GFP+/Iba1+; Fig. 2B). There were still some precursors that were mostly associated to blood vessels (GFP+/Iba1– round cells; Fig. 2B, supplemental online Fig. 2), but all these cells differentiate into highly ramified microglia at later time points [2]. Both resident (GFP–/Iba1+; Fig. 2B) and bone marrow-derived microglia responded to the endotoxin challenge. Indeed, transcriptional activation of TLR2 indicates that LPS is an appropriate model to activate microglia, including those of bone marrow origin (Fig. 2C). These data provide evidence that infiltration and activation of microglia take place in the CNS following a single endotoxin challenge. We then determined whether such phenomena were altered in response to irradiation and bone marrow transplant.
View larger version (78K):
[in this window]
[in a new window]
|
Figure 2. GFP-expressing cells in the brains of chimeric mice after intracerebral lipopolysaccharide injection. (A): Fluorescent-activated cell sorting results from the blood of an irradiated C57BL/6 mouse having received a bone marrow graft from GFP-expressing mice. Cells were analyzed and sorted according to phycoerythrin-CD11b and GFP fluorescence. Typically, a chimerism of 95% and higher is observed (96.17% here). (B): Low (top) and high (dashed area blown up at bottom) magnification fluorescent photomicrographs of brain sections 24 hours following intracerebral lipopolysaccharide (LPS) injection in chimeric mice. Green (GFP) cells are bone-marrow-derived, whereas microglia were labeled using an antibody directed against iba1 (red). Merge (right) reveals that all the differentiated GFP-positive cells were also iba1-positive (yellow, full arrows). Most of the undifferentiated GFP-positive cells (green, empty arrows) were found near bv. GFP-negative resident microglia (red, double-headed arrows) were also present. (C): Dark (left) and bright (middle) field photomicrographs of brain sections 24 hours following intracerebral LPS. Activated microglia were determined by combination of immunohistochemistry (brown staining in middle and right) using antibodies directed against GFP (top) or iba1 (bottom) and in situ hybridization for TLR2 (silver grains). Higher magnification (dashed area in middle blown up on right) reveals double labeling of GFP (top, arrows) and iba1 (bottom, arrows) positive cells with TLR2. Abbreviations: bv, blood vessels; GFP, green fluorescent protein; iba1, ionized calcium-binding adapter molecule 1; TLR2, Toll-like receptor 2.
|
|
Expression of Immune Transcripts in the Brains of C57BL/6, GFP, and Chimeric Mice
Densitometric profiles of the proinflammatory markers TLR2, TNF-, IL-1β, and MCP-1 were analyzed at two different time points (6 and 24 hours after LPS injection) in the three groups (n = 5 per group per time point; Figs. 3, 4, 6). The spatial distribution of the four markers was similar in each group, and ANOVA revealed a main effect for group (Pillai's trace, f (8, 44) = 2.212, p = .045) and time (Pillai's Trace, f (4, 21) = 5.380, p = .04) but no group x time interactions (Pillai's Trace, f (8, 44) = 0.887, p = .535). Pairwise group comparisons revealed only a difference between C57BL/6 and GFP mice for IL-1β (p = .032, Bonferroni adjusted; Fig. 5). Indeed, IL-1 expression levels were significantly lower in C57BL/6 mice than GFP animals (Fig. 5). All other group comparisons were not significant for any other markers. It was not possible to perform post hoc group comparisons at specific time points because there was no significant group x time interaction. In most instances, C57BL/6 mice exhibited marginally weaker signals than the two other groups, but this difference did not prove to be significant save for IL-1β. As depicted by Figures 3
–6 (contralateral sides), there was no constitutive expression of these immune genes in the brains of the three groups of mice. These data indicate that the innate immune response is not compromised or exacerbated in chimeric mice compared with nonirradiated recipients and donors.
View larger version (70K):
[in this window]
[in a new window]
|
Figure 3. Toll-like receptor 2 (TLR2) mRNA in the brains of C57BL/6, green fluorescent protein-expressing, and chimeric mice after intracerebral lipopolysaccharide (LPS) injection. Dark-field photomicrographs of brain sections hybridized with a TLR2 cRNA probe and dipped into NTB emulsion milk. LPS (1 µg/µl) was administered in the brains of C57BL/6 (C57), GFP-expressing, and chimeric mice. Mice were killed at time 6 and 24 hours postinjection. Bottom panel shows quantitative analysis of TLR2 (O.D.) in the ipsilateral side of C57, GFP, and chimera groups (n = 5 per group, data presented as mean ± SEM). No differences were found among the groups. Abbreviations: C57, C57BL/6; GFP, green fluorescent protein; h, hours; O.D., optical density.
|
|
View larger version (60K):
[in this window]
[in a new window]
|
Figure 4. Expression of tumor necrosis factor mRNA in the brains of C57BL/6, GFP-expressing, and chimeric mice after intracerebral lipopolysaccharide injection. Please see details in Figure 3 legend. Abbreviations: C57, C57BL/6; GFP, green fluorescent protein; h, hours; O.D., optical density.
|
|
View larger version (66K):
[in this window]
[in a new window]
|
Figure 5. Lipopolysaccharide caused transcriptional activation of the gene encoding interleukin 1β in the brains of C57BL/6, GFP-expressing, and chimeric mice. Pairwise group comparisons revealed a significant main effect between the C57 and GFP group (*, p = .032, Bonferroni adjusted). No specific pairwise comparisons at each time point could be done due to lack of a group x time interaction. Note that the chimera group was not significantly different from the C57 or GFP group. Please see details in Figure 3 legend. Abbreviations: C57, C57BL/6; GFP, green fluorescent protein; h, hours; O.D., optical density.
|
|
View larger version (50K):
[in this window]
[in a new window]
|
Figure 6. Monocyte chemoattractant protein 1 gene expression in the brains of C57BL/6, GFP-expressing, and chimeric mice after intracerebral lipopolysaccharide injection. Please see details in Figure 3 legend. Abbreviations: C57, C57BL/6; GFP, green fluorescent protein; h, hours; O.D., optical density.
|
|
|
DISCUSSION
|
|---|
There is clear evidence that the makeup of the monocytic cell population in the CNS is heterogeneous [21, 22]. The difference in the roles for resident microglia and invading macrophages could be harnessed to take advantage of the benefits of both populations in potential therapeutic treatment of neuropathologies. Thus, a practical tool that does not alter the immune response of these cells or of the host is needed to study the progress and function of these two populations in health and pathological models. Our experiment outlines the use of chimeric mice that received bone marrow-derived stem cell grafts from GFP-expressing donors following whole-body irradiation. We re-emphasized that the invading macrophages (GFP+/Iba1+) can be clearly distinguished from the resident microglia (GFP–/Iba1+). Furthermore, our results support that the innate immune response of the chimeric mice is similar to that of C57BL/6 and GFP mice. More specifically, there are no quantitative differences in the expression of the innate immune markers TLR2, TNF-, and MCP-1 in the brains of chimeric mice following LPS administration in comparison with C57BL/6 and GFP-expressing mice. It is important to note that some qualitative difference for the expression of TLR2 could be seen at the two time points, as the signal in the C57BL/6 did not seem to spread to the contralateral side as much as the GFP and chimeric mice (Fig. 3). However, this difference did not prove to translate into a significantly stronger signal for the GFP and chimeric mice. Furthermore, the chimeric mice showed an intermediate expression compared with the C57BL/6 and GFP mice, as expected. Only marginal differences in the expression of IL-1β can be detected between C57BL/6 and GFP-expressing mice. Although earlier work had raised concerns about the BBB integrity [11], increased TNF- expression, and microgliosis [13] in the irradiated mice, these transient changes seem to have little long-term consequences on the innate immune response in the CNS. Moreover, we did not find a constitutive expression of these immune transcripts in the brains of the three groups of mice. Their immune status is therefore very similar, at least in the CNS. To be sure, as noted earlier, we have observed slight differences in the immune responses of chimeric mice and mice from their host and donor lineages. Nevertheless, the overall response of the chimeric mice to LPS seems quite normal, and nothing suggests abnormalities that would compromise or exacerbate the innate immune status of the chimeric mice. This point is crucial to establish the validity of using chimeric mice as a tool to study the contribution of graft-derived macrophages infiltrating the CNS in models of neuropathies.
This in vivo approach has already helped to unravel the respective roles of bone marrow-derived and resident microglial cells in models of AD [9, 10], meningitis [5], excitotoxicity [23], ischemia [7], and amyotrophic lateral sclerosis [24]. The present study provides essential data because numerous concerns were raised in regard to the effects of lethal irradiation on the ability of microglia to behave normally. Here we show that no obvious defects were found in the brains of chimeric mice when compared with their control mice, which justifies the use of this model to study the role of bone marrow-derived microglia. Furthermore, the advent of chimeras has sparked many discussions about the possible therapeutic uses of the bone marrow-derived stem cells (for reviews, see [10, 25–27]). Supporting this claim, bone marrow-derived macrophages were recently found to be more competent in eliminating beta amyloid debris compared with their resident counterparts in a mouse model of AD [9]. Consequently, finding a way to enhance the chemoattraction of these cells or easing their passage through the BBB could prove useful in alleviating the amyloid load in the brain of AD patients. To be sure, the use of irradiation to eliminate a patient's current immune cell is not a viable option. However, adding more competent and/or genetically enhanced compatible progenitor cells to a patient's arsenal could improve treatment.
|
DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST
|
|---|
The authors indicate no potential conflicts of interest.
|
ACKNOWLEDGMENTS
|
|---|
The Canadian Institutes in Health Research supported this research. N.P.T. is the recipient of a postdoctoral fellowship from the Multiple Sclerosis Society of Canada. S.R. holds a Canadian Research Chair in Neuroimmunology.
|
REFERENCES
|
|---|
- Turrin NP, Rivest S. Unraveling the molecular details involved in the intimate link between the immune and neuroendocrine systems. Exp Biol Med (Maywood) 2004;229:996–1006.[Abstract/Free Full Text]
- Simard AR, Rivest S. Bone marrow stem cells have the ability to populate the entire central nervous system into fully differentiated parenchymal microglia. FASEB J 2004;18:998–1000.[Abstract/Free Full Text]
- Bechmann I, Priller J, Kovac A et al. Immune surveillance of mouse brain perivascular spaces by blood-borne macrophages. Eur J Neurosci 2001;14:1651–1658.[CrossRef][Medline]
- Priller J, Prinz M, Heikenwalder M et al. Early and rapid engraftment of bone marrow-derived microglia in scrapie. J Neurosci 2006;26:11753–11762.[Abstract/Free Full Text]
- Djukic M, Mildner A, Schmidt H et al. Circulating monocytes engraft in the brain, differentiate into microglia and contribute to the pathology following meningitis in mice. Brain 2006;129Pt 9:2394–2403.[Abstract/Free Full Text]
- Tanaka R, Komine-Kobayashi M, Mochizuki H et al. Migration of enhanced green fluorescent protein expressing bone marrow-derived microglia/macrophage into the mouse brain following permanent focal ischemia. Neuroscience 2003;117:531–539.[CrossRef][Medline]
- Schilling M, Besselmann M, Muller M et al. Predominant phagocytic activity of resident microglia over hematogenous macrophages following transient focal cerebral ischemia: An investigation using green fluorescent protein transgenic bone marrow chimeric mice. Exp Neurol 2005;196:290–297.[CrossRef][Medline]
- Liu M, Eguchi N, Yamasaki Y et al. Focal cerebral ischemia/reperfusion injury in mice induces hematopoietic prostaglandin D synthase in microglia and macrophages. Neuroscience 2007;145:520–529.[CrossRef][Medline]
- Simard AR, Soulet D, Gowing G et al. Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer's disease. Neuron 2006;49:489–502.[CrossRef][Medline]
- Simard AR, Rivest S. Neuroprotective properties of the innate immune system and bone marrow stem cells in Alzheimer's disease. Mol Psychiatry 2006;11:327–335.[CrossRef][Medline]
- Diserbo M, Agin A, Lamproglou I et al. Blood-brain barrier permeability after gamma whole-body irradiation: An in vivo microdialysis study. Can J Physiol Pharmacol 2002;80:670–678.[CrossRef][Medline]
- Belka C, Budach W, Kortmann RD et al. Radiation induced CNS toxicity—molecular and cellular mechanisms. Br J Cancer 2001;85:1233–1239.[CrossRef][Medline]
- Mildenberger M, Beach TG, McGeer EG et al. An animal model of prophylactic cranial irradiation: Histologic effects at acute, early and delayed stages. Int J Radiat Oncol Biol Phys 1990;18:1051–1060.[Medline]
- Monje ML, Mizumatsu S, Fike JR et al. Irradiation induces neural precursor-cell dysfunction. Nat Med 2002;8:955–962.[CrossRef][Medline]
- Laflamme N, Soucy G, Rivest S. Circulating cell wall components derived from gram-negative, not gram-positive, bacteria cause a profound induction of the gene-encoding Toll-like receptor 2 in the CNS. J Neurochem 2001;79:648–657.[CrossRef][Medline]
- Laflamme N, Lacroix S, Rivest S. An essential role of interleukin-1beta in mediating NF-kappaB activity and COX-2 transcription in cells of the blood-brain barrier in response to a systemic and localized inflammation but not during endotoxemia. J Neurosci 1999;19:10923–10930.[Abstract/Free Full Text]
- Laflamme N, Echchannaoui H, Landmann R et al. Cooperation between toll-like receptor 2 and 4 in the brain of mice challenged with cell wall components derived from gram-negative and gram-positive bacteria. Eur J Immunol 2003;33:1127–1138.[CrossRef][Medline]
- Nadeau S, Rivest S. Glucocorticoids play a fundamental role in protecting the brain during innate immune response. J Neurosci 2003;23:5536–5544.[Abstract/Free Full Text]
- Turrin NP, Rivest S. Innate immune reaction in response to seizures: Implications for the neuropathology associated with epilepsy. Neurobiol Dis 2004;16:321–334.[CrossRef][Medline]
- Paxinos G, Franklin KBJ. The Mouse Brain in Stereotaxic Coordinates. 2nd ed San Diego: Academic Press,2001;.
- Kaur C, Hao AJ, Wu CH et al. Origin of microglia. Microsc Res Tech 2001;54:2–9.[CrossRef][Medline]
- Davoust N, Vuaillat C, Cavillon G et al. Bone marrow CD34+/B220+ progenitors target the inflamed brain and display in vitro differentiation potential toward microglia. FASEB J 2006;20:2081–2092.[Abstract/Free Full Text]
- Guo Z, Iyun T, Fu W et al. Bone marrow transplantation reveals roles for brain macrophage/microglia TNF signaling and nitric oxide production in excitotoxic neuronal death. Neuromolecular Med 2004;5:219–234.[CrossRef][Medline]
- Beers DR, Henkel JS, Xiao Q et al. Wild-type microglia extend survival in PU.1 knockout mice with familial amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A 2006;103:16021–16026.[Abstract/Free Full Text]
- Mezey E. Bone marrow-derived stem cells in neurological diseases: Stones or masons? Regen Med 2007;2:37–49.[CrossRef][Medline]
- Chang YC, Shyu WC, Lin SZ et al. Regenerative therapy for stroke. Cell Transplant 2007;16:171–181.[Medline]
- Brodhun M, Bauer R, Patt S. Potential stem cell therapy and application in neurotrauma. Exp Toxicol Pathol 2004;56:103–112.[CrossRef][Medline]
This article has been cited by other articles:
|
|
|
|
 
D. R. Getts, R. L. Terry, M. T. Getts, M. Muller, S. Rana, B. Shrestha, J. Radford, N. Van Rooijen, I. L. Campbell, and N. J.C. King
Ly6c+ "inflammatory monocytes" are microglial precursors recruited in a pathogenic manner in West Nile virus encephalitis
J. Exp. Med.,
September 29, 2008;
205(10):
2319 - 2337.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
