lipoteichoic-acid and Encephalitis

In contrast to the role of lipopolysaccharide from Gram-negative bacteria, the role of Gram-positive bacterial components in inducing inflammation in the CNS remains controversial. We studied the potency of highly purified lipoteichoic acid and muramyl dipeptide isolated from Staphylococcus aureus to activate primary cultures of rat microglia. Exposure of pure microglial cultures to lipoteichoic acid triggered a significant time- and dose-dependent production of pro-inflammatory cytokines (tumour-necrosis factor-alpha, interleukin-1beta, interleukin-6) and nitric oxide. Muramyl dipeptide strongly and selectively potentiated lipoteichoic acid-induced inducible nitric oxide synthase expression and nitric oxide production. However, it did not have any significant influence on the production of pro-inflammatory cytokines. As bacterial components are recognised by the innate immunity through Toll-like receptors (TLRs) we showed that lipoteichoic acid was recognised in microglia by the TLR2 and lipopolysaccharide by the TLR4, as cells isolated from mice lacking TLR2 or TLR4 did not produce pro-inflammatory cytokines and nitric oxide upon lipoteichoic acid or lipopolysaccharide stimulation, respectively. Lipoteichoic acid-induced glia activation was mediated by p38 and ERK1/2 MAP kinases, as pretreatment with inhibitor of p38 or ERK1/2 decreased lipoteichoic acid-induced cytokine release, iNOS mRNA expression and nitric oxide production. The observed pro-inflammatory response induced by lipoteichoic acid-activated microglia could play a major role in the inflammatory response of CNS induced by Gram-positive bacteria.

Topics: Acetylmuramyl-Alanyl-Isoglutamine; Animals; Animals, Newborn; Cells, Cultured; Central Nervous System Bacterial Infections; Cytokines; Dose-Response Relationship, Drug; Encephalitis; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Inflammation Mediators; Lipopolysaccharides; Microglia; Nitric Oxide; Nitric Oxide Synthase Type II; p38 Mitogen-Activated Protein Kinases; Rats; Signal Transduction; Teichoic Acids; Time Factors; Toll-Like Receptor 2; Toll-Like Receptor 4

In this study we investigated the mechanisms of neuronal cell death induced by lipoteichoic acid (LTA) and muramyl dipeptide (MDP) from Gram-positive bacterial cell walls using primary cultures of rat cerebellum granule cells (CGCs) and rat cortical glial cells (astrocytes and microglia). LTA (+/- MDP) from Staphylococcus aureus induced a strong inflammatory response of both types of glial cells (release of interleukin-1beta, tumour necrosis factor-alpha and nitric oxide). The death of CGCs was caused by activated glia because in the absence of glia (treatment with 7.5 microm cytosine-d-arabinoside to inhibit non-neuronal cell proliferation) LTA + MDP did not cause significant cell death (less than 20%). In addition, staining with rhodamine-labelled LTA confirmed that LTA was bound only to microglia and astrocytes (not neurones). Neuronal cell death induced by LTA (+/- MDP)-activated glia was partially blocked by an inducible nitric oxide synthase inhibitor (1400 W; 100 microm), and completely blocked by a superoxide dismutase mimetic [manganese (III) tetrakis (4-benzoic acid)porphyrin chloride; 50 microm] and a peroxynitrite scavenger [5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrinato iron (III); 100 microm] suggesting that nitric oxide and peroxynitrite contributed to LTA-induced cell death. Moreover, neuronal cell death was inhibited by selective inhibitors of caspase-3 (z-DEVD-fmk; 50 microm) and caspase-8 (z-Ile-Glu(O-Me)-Thr-Asp(O-Me) fluoromethyl ketone; 50 microm) indicating that they were involved in LTA-induced neuronal cell death.

Topics: Acetylmuramyl-Alanyl-Isoglutamine; Analysis of Variance; Animals; Animals, Newborn; Caspases; Cell Death; Cell Proliferation; Cells, Cultured; Cytarabine; Dose-Response Relationship, Drug; Drug Interactions; Encephalitis; Enzyme Activation; Enzyme Inhibitors; Glial Fibrillary Acidic Protein; Interleukin-1; Interleukin-6; Lectins; Lipopolysaccharides; Models, Biological; Neurodegenerative Diseases; Neuroglia; Nitrites; Oxidative Stress; Rats; Receptors, Interleukin-1; Staphylococcus aureus; Teichoic Acids; Time Factors; Tumor Necrosis Factor-alpha

Rabbits were immunized with staphylococcal lipoteichoic acid (LTA) in Freund's adjuvant. After four injections (six weeks) the rabbits showed decreased activity and unsteadiness of the head. Two weeks after the sixth injection (ten weeks), two of five rabbits developed clinical signs of encephalitis with nystagmus, ataxia, general weakness, decreased activity, and dragging of the hind legs. The other three animals showed only mild symptoms. Neuropathological examination showed inflammatory infiltrates containing small lymphocytes and some plasma cells in the leptomeninges and within the perivascular spaces of the brain.

Topics: Animals; Antibodies, Bacterial; Antigens, Bacterial; Brain; Encephalitis; Lipopolysaccharides; Phosphatidic Acids; Rabbits; Staphylococcus aureus; Teichoic Acids