Selective transfer of exosomes from oligodendrocytes to microglia by macropinocytosis.

The transfer of antigens from oligodendrocytes to immune cells has been implicated in the pathogenesis of autoimmune diseases. Here, we show that oligodendrocytes secrete small membrane vesicles called exosomes, which are specifically and efficiently taken up by microglia both in vitro and in vivo. Internalisation of exosomes occurs by a macropinocytotic mechanism without inducing a concomitant inflammatory response. After stimulation of microglia with interferon-γ, we observe an upregulation of MHC class II in a subpopulation of microglia. However, exosomes are preferentially internalised in microglia that do not seem to have antigen-presenting capacity. We propose that the constitutive macropinocytotic clearance of exosomes by a subset of microglia represents an important mechanism through which microglia participate in the degradation of oligodendroglial membrane in an immunologically 'silent' manner. By designating the capacity for macropinocytosis and antigen presentation to distinct cells, degradation and immune function might be assigned to different subtypes of microglia.

Toll-like receptor activation reveals developmental reorganization and unmasks responder subsets of microglia.

The sentinel and immune functions of microglia require rapid and appropriate reactions to infection and damage. Their Toll-like receptors (TLRs) sense both as threats. However, whether activated microglia mount uniform responses or whether subsets conduct selective tasks is unknown. We demonstrate that murine microglia reorganize their responses to TLR activations postnatally and that this process comes with a maturation of TLR4-organized functions. Although induction of MHCI for antigen presentation remains as a pan-populational feature, synthesis of TNFα becomes restricted to a subset, even within adult central nervous system regions. Response heterogeneity is evident ex vivo, in situ, and in vivo, but is not limited to TNFα production or to TLR-triggered functions. Also, clearance activities for myelin under physiological and pathophysiological conditions, IFNγ-enforced upregulation of MHCII, or challenged inductions of other proinflammatory factors reveal dissimilar microglial contributions. Notably, response heterogeneity is also confirmed in human brain tissue. Our findings suggest that microglia divide by constitutive and inducible capacities. Privileged production of inflammatory mediators assigns a master control to subsets. Sequestration of clearance of endogenous material versus antigen presentation in exclusive compartments can separate potentially interfering functions. Finally, subsets rather than a uniform population of microglia may assemble the reactive phenotypes in responses during infection, injury, and rebuilding, warranting consideration in experimental manipulation and therapeutic strategies.

MotiQ: an open-source toolbox to quantify the cell motility and morphology of microglia.

Microglia are the primary resident innate immune cells of the CNS. They possess branched, motile cell processes that are important for their cellular functions. To study the pathways that control microglial morphology and motility under physiological and disease conditions, it is necessary to quantify microglial morphology and motility precisely and reliably. Several image analysis approaches are available for the quantification of microglial morphology and motility. However, they are either not automated, not freely accessible, and/or limited in the number of morphology and motility parameters that can be assessed. Thus, we have developed MotiQ, an open-source, freely accessible software for automated quantification of microglial motility and morphology. MotiQ allows quantification of a diverse set of cellular motility and morphology parameters, including the parameters that have become the gold standard in the microglia field. We demonstrate that MotiQ can be applied to in vivo, ex vivo, and in vitro data from confocal, epifluorescence, or two-photon microscopy, and we compare its results to other analysis approaches. We suggest MotiQ as a versatile and customizable tool to study microglia.

Quantified CSF antibody reactivity against myelin in multiple sclerosis.

BACKGROUND: Synthesis of clonal IgG is a consistent feature of patients with multiple sclerosis (MS). Whether oligoclonal bands (OCBs) represent unspecific disease bystanders or active components in MS pathology is an open question. The aim of this study was to develop a method to quantify and compare the reactivity of cerebrospinal fluid (CSF) antibodies from patients with and without MS. METHODS: We collected CSF from 262 patients from two different cohorts, which included 148 patients with MS and 114 with other neurological diseases (OND). We established a highly sensitive electrochemiluminescence (ECL)-based assay to measure CSF antibody reactivity against purified myelin particles and biotin anchored liposomes. The diagnostic value of the ECL score against myelin particles was assessed with receiver operating characteristic curves. RESULTS: CSF from patients with MS have higher reactivity toward purified myelin particles as compared to those with OND with OCBs. Using liposomes with defined lipid compositions and myelin particles from ceramide synthase 2 (CerS2) knockout mice, we find that some of the CSF antibody reactivity is directed against cerebrosides. CONCLUSION: The ECL-based assay system expands the currently available toolbox for the detection of autoantibodies in MS and related diseases.

Assessing ß-amyloid-induced NLRP3 inflammasome activation in primary microglia.

Senile plaques are an important histological hallmark of Alzheimer's disease. They mainly consist of the fibrillar peptide ß-amyloid (Aß) and are surrounded by activated microglia and astrocytes. Microglia in the vicinity of senile plaques express high levels of proinflammatory cytokines and neurotoxic substances, which are believed to influence disease progression. One important cytokine in Alzheimer's disease is IL-1ß. Stimulation of cultured primary microglia by synthetic fibrillar Aß causes the release of IL-1ß via activation of the NLRP3 inflammasome.Here we provide protocols for the preparation of primary microglial cultures and synthetic oligomeric and fibrillar forms of Aß.