Microglia are the resident innate immune cells of the central nervous system (CNS) parenchyma. To determine the impact of microglia on disease development and progression in neurodegenerative and neuroinflammatory diseases, it is essential to distinguish microglia from peripheral macrophages/monocytes, which are eventually equally recruited. It has been suggested that transmembrane protein 119 (TMEM119) serves as a reliable microglia marker that discriminates resident microglia from blood‐derived macrophages in the human and murine brain. Here, we investigated the validity of TMEM119 as a microglia marker in four in vivo models (cuprizone intoxication, experimental autoimmune encephalomyelitis (EAE), permanent filament middle cerebral artery occlusion (fMCAo), and intracerebral 6‐hydroxydopamine (6‐OHDA) injections) as well as post mortem multiple sclerosis (MS) brain tissues. In all applied animal models and post mortem MS tissues, we found increased densities of ionized calcium‐binding adapter molecule 1+ (IBA1+) cells, paralleled by a significant decrease in TMEM119 expression. In addition, other cell types in peripheral tissues (i.e., follicular dendritic cells and brown adipose tissue) were also found to express TMEM119. In summary, this study demonstrates that TMEM119 is not exclusively expressed by microglia nor does it label all microglia, especially under cellular stress conditions. Since novel transgenic lines have been developed to label microglia using the TMEM119 promotor, downregulation of TMEM119 expression might interfere with the results and should, thus, be considered when working with these transgenic mouse models.

The loss of myelinating oligodendrocytes is a key characteristic of many neurological diseases, including Multiple Sclerosis (MS). In progressive MS, where effective treatment options are limited, peripheral immune cells can be found at the site of demyelination and are suggested to play a functional role during disease progression. In this study, we hypothesize that metabolic oligodendrocyte injury, caused by feeding the copper chelator cuprizone, is a potent trigger for peripheral immune cell recruitment into the central nervous system (CNS). We used immunohistochemistry and flow cytometry to evaluate the composition, density, and activation status of infiltrating T lymphocytes in cuprizone‐intoxicated mice and post‐mortem progressive MS tissues. Our results demonstrate a predominance of CD8+ T cells along with high proliferation rates and cytotoxic granule expression, indicating an antigenic and pro‐inflammatory milieu in the CNS of cuprizone‐intoxicated mice. Numbers of recruited T cells and the composition of lymphocytic infiltrates in cuprizone‐intoxicated mice were found to be comparable to those found in progressive MS lesions. Finally, amelioration of the cuprizone‐induced pathology by treating mice with laquinimod significantly reduces the number of recruited T cells. Overall, this study provides strong evidence that toxic demyelination is a sufficient trigger for T cells to infiltrate the demyelinated CNS. Further investigation of the mode of action and functional consequence of T cell recruitment might offer promising new therapeutic approaches for progressive MS.

Background: An important hallmark of Alzheimer's disease (AD) is the increase of Aβ1-42 burden and its accumulation to senile plaques, leading the reactive gliosis and neurodegeneration. The modulation of glia cell function represents an attractive therapeutic strategy, but is currently limited by an incomplete understanding of its relevance for AD. The chemotactic G-protein coupled formyl peptide receptor (FPR), which is known to modulate Aβ1-42 uptake and signal transduction, might be one candidate molecule regulating glia function in AD. Here, we investigate whether the modulation of FPR exerts beneficial effects in an AD preclinical model. Methods: To address this question, APP/PS1 double-transgenic AD mice were treated for 20 weeks with either the pro-inflammatory FPR agonist fMLF, the FPR1/2 antagonist Boc2 or the anti-inflammatory FPR2 agonist Ac2-26. Spatial learning and memory were evaluated using a Morris water maze test. Immunohistological staining, gene expression studies, and flow cytometry analyses were performed to study neuronal loss, gliosis, and Aß-load in the hippocampus and cortex, respectively. Results: FPR antagonism by Boc2-treatment significantly improved spatial memory performance, reduced neuronal pathology, induced the expression of homeostatic growth factors, and ameliorated microglia, but not astrocyte, reactivity. Furthermore, the elevated levels of amyloid plaques in the hippocampus were reduced by Boc2treatment, presumably by an induction of amyloid degradation. Conclusions: We suggest that the modulation of FPR signaling cascades might be considered as a promising therapeutic approach for alleviating the cognitive deficits associated with early AD. Additional studies are now needed to address the downstream effectors as well as the safety profile of Boc2.

Experimental autoimmune encephalomyelitis (EAE) is the most commonly used multiple sclerosis animal model. EAE mice typically develop motor deficits in a caudal-to-rostral pattern when inflammatory lesions have already developed. However, to monitor more subtle behavioral deficits during lesion development (i.e., pre-clinical phase), more sophisticated methods are needed. Here, we investigated whether high speed ventral plane videography can be applied to monitor early motor deficits during ‘pre-clinical’ EAE. For this purpose, EAE was induced in C57BL/6 mice and gait abnormalities were quantified using the DigiGait™ apparatus. Gait deficits were related to histopathological changes. 10 out of 10 control (100%), and 14 out of 18 (77.8%) pre-clinical EAE mice could be evaluated using DigiGait™. EAE severity was not influenced by DigiGait™-related mice handlings. Most gait parameters recorded from day 6 post-immunization until the end of the experiment were found to be stable in control mice. During the pre-clinical phase, when conventional EAE scorings failed to detect any functional impairment, EAE mice showed an increased Swing Time, increased %Swing Stride, decreased %Stance Stride, decreased Stance/Swing, and an increased Absolute Paw Angle. In summary, DigiGait™ is more sensitive than conventional scoring approaches to study motor deficits during the EAE pre-clinical phase.

Microglia play an important role in the pathology of various central nervous system disorders, including multiple sclerosis (MS). While different methods exist to evaluate the extent of microglia activation, comparative studies investigating the sensitivity of these methods are missing for most models. In this study, we systematically evaluated which of the three commonly used histological methods (id est, quantification of microglia density, densitometrically evaluated staining intensity, or cellular morphology based on the determination of a ramification index, all measured in anti-ionized calcium-binding adaptor protein-1 (IBA1) immunohistochemical stains) is the most sensitive method to detect subtle changes in the microglia activation status in the context of MS. To this end, we used the toxin-induced cuprizone model which allows the experimental induction of a highly reproducible demyelination in several central nervous system regions, paralleled by early microglia activation. In this study, we showed that after 3 weeks of cuprizone intoxication, all methods reveal a significant microglia activation in the white matter corpus callosum. In contrast, in the affected neocortical grey matter, the evaluation of anti-IBA1 cell morphologies was the most sensitive method to detect subtle changes of microglial activation. The results of this study provide a useful guide for future immunohistochemical evaluations in the cuprizone and other neurodegenerative models.

Ectopic lymphoid follicles (ELFs), resembling germinal centre‐like structures, emerge in a variety of infectious and autoimmune and neoplastic diseases. ELFs can be found in the meninges of around 40% of the investigated progressive multiple sclerosis (MS) post‐mortem brain tissues and are associated with the severity of cortical degeneration and clinical disease progression. Of predominant importance for progressive neuronal damage during the progressive MS phase appears to be meningeal inflammation, comprising diffuse meningeal infiltrates, B‐cell aggregates and compartmentalized ELFs. However, the absence of a uniform definition of ELFs impedes reproducible and comparable neuropathological research in this field. In this review article, we will first highlight historical aspects and milestones around the discovery of ELFs in the meninges of progressive MS patients. In the next step, we discuss how animal models may contribute to an understanding of the mechanisms underlying ELF formation. Finally, we summarize challenges in investigating ELFs and propose potential directions for future research.

Multiple sclerosis (MS) is a central nervous system disease characterized by both degenerative and inflammatory processes. Various mediators are involved in the interplay of degeneration and innate immunity on one hand and peripheral adaptive immunity on the other hand. The secreted protein lipocalin 2 (LCN2) is an inflammatory modulator in a variety of pathologies. Although elevated intrathecal levels of LCN2 have been reported in MS patients, it's functional role is widely unknown.Here, we identified a subpopulation of astrocytes as a source of LCN2 in MS lesions and respective animal models. We investigated the functional role of LCN2 for both autoimmune and degenerative aspects in three MS mouse models including both wild type (WT) and Lcn2 À/À mouse strains. While the experimental autoimmune encephalomyelitis (EAE) model reflects primary autoimmunity, the cuprizone model reflects selective oligodendrocyte loss and demyelination. In addition, we included a combinatory Cup/EAE model in which primary cytodegeneration is followed by inflammatory lesions within the forebrain. While in the EAE model, the disease outcome was comparable in between the two mouse strains, cuprizone intoxicated Lcn2 À/À animals showed an increased loss of oligodendrocytes. In the Cup/EAE model, Lcn2 À/À animals showed increased inflammation when compared to WT mice. Together, our results highlight LCN2 as a potentially protective molecule in MS lesion formation, which might be able to limit loss of oligodendrocytes immune-cell invasion. Despite these findings, it is not yet clear which glial cell phenotype (and to which extent) contributes to the observed neuroprotective effects, that is, microglia and/or astroglia or even endothelial cells in the brain.

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