Toll-Like Receptor Stimulation Enhances Phagocytosis and Intracellular Killing of Nonencapsulated and Encapsulated Streptococcus pneumoniae by Murine Microglia

Department of Geriatrics, Evang. Krankenhaus Göttingen-Weende, An der Lutter 24, D-37075 Göttingen, Germany.
Infection and immunity (Impact Factor: 3.73). 11/2009; 78(2):865-71. DOI: 10.1128/IAI.01110-09
Source: PubMed


Toll-like receptors (TLRs) are crucial pattern recognition receptors in innate immunity that are expressed in microglia, the resident macrophages of the brain. TLR2, -4, and -9 are important in the responses against Streptococcus pneumoniae, the most common agent causing bacterial meningitis beyond the neonatal period. Murine microglial cultures were stimulated with agonists for TLR1/2 (Pam(3)CSK(4)), TLR4 (lipopolysaccharide), and TLR9 (CpG oligodeoxynucleotide) for 24 h and then exposed to either the encapsulated D39 (serotype 2) or the nonencapsulated R6 strain of S. pneumoniae. After stimulation, the levels of interleukin-6 and CCL5 (RANTES [regulated upon activation normal T-cell expressed and secreted]) were increased, confirming microglial activation. The TLR1/2, -4, and -9 agonist-stimulated microglia ingested significantly more bacteria than unstimulated cells (P < 0.05). The presence of cytochalasin D, an inhibitor of actin polymerizaton, blocked >90% of phagocytosis. Along with an increased phagocytic activity, the intracellular bacterial killing was also increased in TLR-stimulated cells compared to unstimulated cells. Together, our data suggest that microglial stimulation by these TLRs may increase the resistance of the brain against pneumococcal infections.

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Available from: Sven Hammerschmidt, Sep 30, 2015
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    • "Since bacterial DNA, unlike eukaryotic DNA contains a high rate of unmethylated cytosine-guanine (CpG) motifs [29], recent attention has focused on this epitope, which is a ligand of Toll-like receptor (TLR)-9. Stimulation of microglial cells with CpG oligonucleotides increased phagocytosis of E. coli, Streptococcus pneumoniae and Cryptococcus neoformans and intracellular killing of these pathogens by microglial cells [30-32]. In various animal models, CpG ODN pre-treatment conferred protection against a variety of bloodstream and other extracerebral bacterial infections [33-35]. "
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    ABSTRACT: Background Palmitoylethanolamide (PEA), an endogenous lipid and a congener of anandamide, possesses a wide range of effects related to metabolic and cellular homeostasis including anti-inflammatory and neuroprotective properties. Methods In vitro, we studied the ability of macrophages to phagocytose Escherichia coli K1 after stimulation with increasing doses of PEA. In vivo, wild-type mice were treated with PEA intraperitoneally 12 hours and 30 minutes before infection. Meningoencephalitis or sepsis was induced by intracerebral or intraperitoneal infection with E. coli K1. Results Stimulation of macrophages with PEA for 30 minutes increased the phagocytosis of E. coli K1 without inducing the release of TNFα or CXCL1. Intracellular killing of E. coli K1 was higher in PEA-stimulated than in unstimulated peritoneal macrophages and microglial cells. Pre-treatment with PEA significantly increased survival of mice challenged intracerebrally or intraperitoneally with E. coli K1. This effect was associated with a decreased production of CXCL1, IL-1β and IL-6 in homogenates of spleen and cerebellum in mice treated with PEA. Conclusions Our observations suggest that these protective effects of PEA in mice can increase the resistance to bacterial infections without the hazard of collateral damage by excessive stimulation of phagocytes.
    Journal of Neuroinflammation 06/2014; 11(1):108. DOI:10.1186/1742-2094-11-108 · 5.41 Impact Factor
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    • "These agents also increased intracellular bacterial killing. The presence of a bacterial capsule as one important virulence factor decreased the rate of phagocytosis of E. coli and S. pneumoniae by one order of magnitude compared to unencapsulated strains (Ribes et al., 2009, 2010a,b, 2012). Agonists of the innate immune system also enhanced the phagocytosis of Cryptococcus neoformans (Redlich et al., 2013). "
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    ABSTRACT: In healthy individuals, infections of the central nervous system (CNS) are comparatively rare. Based on the ability of microglial cells to phagocytose and kill pathogens and on clinical findings in immunocompromised patients with CNS infections, we hypothesize that an intact microglial function is crucial to protect the brain from infections. Phagocytosis of pathogens by microglial cells can be stimulated by agonists of receptors of the innate immune system. Enhancing this pathway to increase the resistance of the brain to infections entails the risk of inducing collateral damage to the nervous tissue. The diversity of microglial cells opens avenue to selectively stimulate sub-populations responsible for the defence against pathogens without stimulating sub-populations which are responsible for collateral damage to the nervous tissue. Palmitoylethanolamide (PEA), an endogenous lipid, increased phagocytosis of bacteria by microglial cells in vitro without a measurable proinflammatory effect. It was tested clinically apparently without severe side effects. Glatiramer acetate increased phagocytosis of latex beads by microglia and monocytes, and dimethyl fumarate enhanced elimination of human immunodeficiency virus from infected macrophages without inducing a release of proinflammatory compounds. Therefore, the discovery of compounds which stimulate the elimination of pathogens without collateral damage of neuronal structures appears an achievable goal. PEA and, with limitations, glatiramer acetate and dimethyl fumarate appear promising candidates.
    Frontiers in Cellular Neuroscience 05/2014; 8:138. DOI:10.3389/fncel.2014.00138 · 4.29 Impact Factor
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    • "Similar to the disposal of the exosome-wrapped myelin, phagocytosis of myelin debris is suppressed by TLR4 activation, although the mechanisms of incorporation per se significantly differ from each other. On the other hand, activity of TLR signaling can rather enhance clearance of pathogens, such as Gram-negative and –positive bacteria (Ribes et al., 2009, 2010), a function that also appears to be associated with microglial subsets. It would be very interesting to determine such a subpopulational split for other clearance cargo as well. "
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    ABSTRACT: Microglia are the principal resident innate immune cells of the CNS. Their contributions to the normal development of the CNS, the maintenance and plasticity of neuronal networks and the safeguarding of proper functionality are becoming more and more evident. Microglia also survey the tissue homeostasis to respond rapidly to exogenous and endogenous threats, primarily with a protective outcome. However, excessive acute activation, chronic activity or an improper adaptation of their functional performance can foster neuropathologies. A key to the versatile response behavior of these cells is their ability to commit to reactive phenotypes, which reveal enormous complexity. Yet the respective profiles of induced genes and installed functions may build up on heterogeneous contributions of cellular subsets. Here, we discuss findings and concepts that consider the variety of microglial activities and response options as being based-at least in part-on a diversity of the engaged cells. Whether it is the production of proinflammatory cytokines, clearance of tissue debris, antigen presentation or the ability to sense neurotransmitters, microglial cells present with an unanticipated heterogeneity of their constitutive and inducible features. While the organizational principles of this heterogeneity are still largely unknown, functional implications are already perceptible.
    Frontiers in Cellular Neuroscience 04/2014; 8(1):101. DOI:10.3389/fncel.2014.00101 · 4.29 Impact Factor
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