Abstract The ability of microglial cells to phagocytose bacteria after stimulation with the endocannabinoid palmitoylethanolamide (PEA) was studied in vitro. PEA increased the phagocytosis of ...unencapsulated Streptococcus pneumoniae R6 and encapsulated Escherichia coli K1 by murine microglial cells significantly after 30 min of microglial stimulation. This suggested that stimulation of microglial cells by PEA can increase the resistance of the brain against CNS infections.
Background and Purpose
Streptococcus pneumoniae is the most common cause of bacterial meningitis in adults and is characterized by high lethality and substantial cognitive disabilities in survivors. ...Here, we have studied the capacity of an established therapeutic agent, magnesium, to improve survival in pneumococcal meningitis by modulating the neurological effects of the major pneumococcal pathogenic factor, pneumolysin.
Experimental Approach
We used mixed primary glial and acute brain slice cultures, pneumolysin injection in infant rats, a mouse meningitis model and complementary approaches such as Western blot, a black lipid bilayer conductance assay and live imaging of primary glial cells.
Key Results
Treatment with therapeutic concentrations of magnesium chloride (500 mg·kg−1 in animals and 2 mM in cultures) prevented pneumolysin‐induced brain swelling and tissue remodelling both in brain slices and in animal models. In contrast to other divalent ions, which diminish the membrane binding of pneumolysin in non‐therapeutic concentrations, magnesium delayed toxin‐driven pore formation without affecting its membrane binding or the conductance profile of its pores. Finally, magnesium prolonged the survival and improved clinical condition of mice with pneumococcal meningitis, in the absence of antibiotic treatment.
Conclusions and Implications
Magnesium is a well‐established and safe therapeutic agent that has demonstrated capacity for attenuating pneumolysin‐triggered pathogenic effects on the brain. The improved animal survival and clinical condition in the meningitis model identifies magnesium as a promising candidate for adjunctive treatment of pneumococcal meningitis, together with antibiotic therapy.
Background. The adaptive immune system has been considered to play a minimal role in the early host response during bacterial meningitis. Methods. We investigated the progression and outcome of ...pneumococcal meningitis in Ragl-/- mice lacking functional B and T cells by assessing overall and symptom-free survival, bacteriological and histological studies, as well as flow cytometry and measurements of proinflammatory mediators. Results. The intracerebral injection of S. pneumoniae D39 induced the recruitment of B and T cells (CD4⁺, γδ and natural killer) into the brain of wild-type mice. Mice with no functional B and T cells developed clinical symptoms and succumbed to the infection earlier than the wild-type group. In the CNS, Ragl-/- mice showed lower levels of interleukin 1β, reduced microglial proliferation, and impaired granulocyte recruitment with an earlier spread of pneumococci into the bloodstream, compared with wild-type mice. Lack of B and T cells resulted in a severe impairment of bacterial clearance in blood, spleen, and liver and an exaggerated systemic inflammatory response. Conclusions. B and T cells are important effector cells delaying the spread of pneumococci from the brain to the systemic circulation and shaping the immune response, thereby prolonging the survival of the host in the absence of antibiotic treatment.
Microglia, innate immune cells of the CNS, sense infection and damage through overlapping receptor sets. Toll‐like receptor (TLR) 4 recognizes bacterial lipopolysaccharide (LPS) and multiple ...injury‐associated factors. We show that its co‐receptor CD14 serves three non‐redundant functions in microglia. First, it confers an up to 100‐fold higher LPS sensitivity compared to peripheral macrophages to enable efficient proinflammatory cytokine induction. Second, CD14 prevents excessive responses to massive LPS challenges via an interferon β‐mediated feedback. Third, CD14 is mandatory for microglial reactions to tissue damage‐associated signals. In mice, these functions are essential for balanced CNS responses to bacterial infection, traumatic and ischemic injuries, since CD14 deficiency causes either hypo‐ or hyperinflammation, insufficient or exaggerated immune cell recruitment or worsened stroke outcomes. While CD14 orchestrates functions of TLR4 and related immune receptors, it is itself regulated by TLR and non‐TLR systems to thereby fine‐tune microglial damage‐sensing capacity upon infectious and non‐infectious CNS challenges. GLIA 2016;64:635–649.
Main points
CD14 controls microglial sensitivity and responses to LPS in a cell‐specific manner.
CD14 prevents excessive CXCL1 production via an IFNβ‐mediated negative feedback.
CD14 acts as a mandatory gate keeper for microglial and CNS responses to damage.
Stimulation of murine primary microglia with Toll-like receptor (TLR) agonists enhances their ability to phagocytose and kill bacteria. Here we show that the viral TLR3 agonist poly(I:C) stimulates ...the release of cyto-/chemokines and nitric oxide by microglia. Poly(I:C) increases microglial phagocytosis and intracellular killing of
Escherichia coli K1, a pathogenic encapsulated bacterial strain, after 30 and 90
min of co-incubation. Stimulation with a viral epitope may strengthen the resistance of the brain to bacterial infections
in vivo. Our data encourage animal experiments with poly(I:C) derivatives to assess whether this approach can increase the resistance of the CNS against bacterial infections.
Background Toll-Like receptors (TLRs) belong to the family of pattern-recognition receptors with a crucial function of recognising pathogen-associated molecular patterns (PAMPs). Cryptococcal ...meningitis is a potentially fatal disease with a high mortality and risk of neurological sequelae. Methods We studied the ability of microglial cells to increase the phagocytosis of cryptococci after stimulation with agonists of TLR1/2, TLR3, TLR4 and TLR9. Results Stimulation of murine microglial cells with these TLR agonists for 24 h increased the phagocytosis of encapsulated Cryptococcus neoformans. Stimulation increased the release of TNF-alpha, CXCL1 (KC), IL-6, IL-10 and MIP-2, which indicated the activation of microglial cells. Unstimulated and TLR agonist-stimulated MyD88-deficient cells showed a reduced ability to phagocytose cryptococci compared to their wild-type counterpart. Intracellular killing of cryptococci was also increased in TLR-stimulated cells compared to unstimulated microglial cells. Conclusion Our observation suggests that stimulation of microglial cells by TLR agonists can increase the resistance of the brain against CNS infections caused by Cryptococcus neoformans. This may be of interest when an immunocompromised patient is unable to eliminate Cryptococcus neoformans despite antifungal therapy. Keywords: Toll-like receptor, Meningitis, Cryptococcosis, Microglia, Phagocytosis
Activated microglia is considered to be involved in the progression of Alzheimer's disease (AD). We investigated the effect of amyloid-β(1-40) (Aβ(40) and exogenous agonists of Toll-like receptor ...(TLR) 1/2 (Pam(3)CSK(4)) and TLR4 (LPS) on neurons in primary murine neuron-microglia co-cultures. Neuronal viability, assessed by quantifying the number of intact neuronal extensions and their crossings using a newly developed Definiens Cognition Network Technology-based method, was significantly decreased after treatment with Pam(3)CSK(4), LPS, and Aβ(40). Combined treatment with Aβ(40) and Pam(3)CSK(4) or LPS had an additive effect. Hence, in patients with AD, synergistic microglial activation by Aβ and bacterial products during infections might contribute to disease progression.
Incidence and mortality of bacterial meningitis are strongly increased in aged compared to younger adults demanding new strategies to improve prevention and therapy of bacterial central nervous ...system (CNS) infections the elderly. Here, we established a geriatric mouse model for an intracerebral E. coli infection which reflects the clinical situation in aged patients: After intracerebral challenge with E. coli K1, aged mice showed a higher mortality, a faster development of clinical symptoms, and a more pronounced weight loss. Elimination of bacteria and systemic inflammatory response were impaired in aged mice, however, the number of infiltrating leukocytes and microglial cells in the CNS of aged and young mice did not differ substantially. In vitro, primary microglial cells and peritoneal macrophages from aged mice phagocytosed less E. coli and released less NO and cyto-/chemokines compared to cells from young mice both without activation and after stimulation by agonists of TLR 2, 4, and 9. Our results suggest that the age-related decline of microglia and macrophage functions plays an essential role for the higher susceptibility of aged mice to intracerebral infections. Strategies to improve the phagocytic potential of aged microglial cells and macrophages appear promising for prevention and treatment of CNS infections in elderly patients.
ABSTRACTDespite the development of new antibiotic agents, mortality of pneumococcal meningitis remains high. In addition, meningitis results in severe long-term morbidity, most prominently cognitive ...deficits. Granulocyte colony-stimulating factor (G-CSF) stimulates proliferation and differentiation of hematopoietic progenitor cells and increases the number of circulating neutrophil granulocytes. This study investigated the effect of adjuvant G-CSF treatment on cognitive function after pneumococcal meningitis. C57BL/6 mice were infected by subarachnoid injection of Streptococcus pneumoniae serotype 3 and treated with ceftriaxone and G-CSF subcutaneously or ceftriaxone alone for 5 days. Clinical scores, motor performance, and mortality during bacterial meningitis were unaffected by adjuvant G-CSF treatment. No effect of G-CSF treatment on production of proinflammatory cytokines or activation of microglia or astrocytes was observed. The G-CSF treatment did, however, result in hippocampal neurogenesis and improved spatial learning performance 6 weeks after meningitis. These results suggest that G-CSF might offer a new adjuvant therapeutic approach in bacterial meningitis to reduce long-term cognitive deficits.
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