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Vergleich primärer Peritonealmakrophagen und Mikrogliazellen von jungen und alten Mäusen bezüglich ihrer Bakterienphagozytose und Freisetzung inflammatorischer Mediatoren in vitro

Comparison of primary peritoneal macrophages and microglial cells from young and aged mice regarding their phagocytosis of bacteria and release of inflammatory mediators in vitro

Annika Kaufmann
Doctoral thesis
Date of Examination: 2016-11-23
Date of issue: 2016-10-26
Advisor: Schütze, Sandra PD Dr.
Referee: Schütze, Sandra PD Dr.
Referee: Lühder, Fred PD Dr.

Persistent Address: http://hdl.handle.net/11858/00-1735-0000-002B-7C48-3

 

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Abstract

English

Bacterial infections of the central nervous system (CNS) are life-threatening diseases, which can lead to death in an acute setting and result in neurological or neuropsychological sequelae as frequent complications. Older persons generally have greater susceptibility to bacterial infections and a much worse outcome after bacterial CNS infections than younger persons. With the increase in average life span for both men and women, the incidence of age-associated infections will expand and present a more serious public health concern. In view of recent rise of antibiotic-resistant bacteria and low response to vaccines in age there is an interest in identifying strategies to protect the elderly against bacterial infections of the CNS. To develop preventive or therapeutic strategies, the underlying mechanisms leading to the increased susceptibility of the elderly to bacterial CNS infections have to be determined. An important part in the early detection of invading pathogenic organisms is the innate immune system. In the CNS microglia and macrophages of meninges, perivascular space, circumventricular organs and choroid plexus represent the main and first line in defense against bacteria. According to the hypothesis of this dissertation the increased susceptibility to bacterial infections of the elderly is caused by age-associated changes in the immune system. The treatise examines the effect of age in relation to important functions of macrophages and microglial cells. On that account primary peritoneal macrophage- and microglial cell cultures were prepared from young (2 months) and aged (18 months) C57BL/6 mice. In vitro macrophages and microglia were characterized and compared regarding their morphology, their ability to phagocytose live E. coli K1, as well as their release of NO and different cyto-/chemokines both without activation and after stimulation by the TLR agonists Pam3CSK4, LPS and CpG. While we could not detect morphological differences between non-stimulated or activated young and aged peritoneal macrophages as well as microglial cells using light microscopy, the age-related changes in the function of macrophages and microglia were even greater. In our study, the ability to phagocytose live E. coli was significantly impaired in aged macrophages and microglial cells in the non-activated state. After TLR activation by bacterial TLR agonists mimicking the situation during a bacterial infection, the difference between aged and young macrophages and microglial cells concerning their phagocytic activity was even more pronounced. Activated aged macrophages and microglial cells phagocytosed significantly less E. coli than activated young macrophages and microglial cells. In addition, we observed a significantly reduced NO release of peritoneal macrophages from aged mice after stimulation with different concentrations of Pam3CSK4, LPS and CpG. Although in microglial cells stimulation could only be performed with selected concentrations of the TLR agonists because of the limited number of available cells, we could demonstrate that similar to peritoneal macrophages, NO release upon TLR activation was lower in aged than in young microglial cells. Furthermore, we compared the release of the cytokines TNF-α and IL-6 and of the chemokine KC by aged and young macrophages and microglia cells in non-stimulated and activated state. In both states aged peritoneal macrophages and microglial cells showed a reduced releasing of TNF-α, IL-6 and KC compared to young peritoneal macrophages and microglial cells. In conclusion, our results suggest that the age-related decline of microglia and macrophage functions, particularly the age-related decline of their phagocytic capacity, plays an essential role for the higher incidence and severe disease progression of bacterial CNS infections in older individuals. Our study identifies resident macrophages and microglial cells as potential therapeutic targets to improve the resistance of the aged host to CNS infections. There are already studies, which examine age-related changes in the expression of Toll-like receptors and intracellular signal transductions as possible causative factors of reduced phagocytic ability and decreased release of proinflammatory mediators by aged macrophages and microglial cells. Especially strategies to increase the phagocytic potential of aged macrophages and microglial cells appear promising for the prevention and therapy of CNS infections in elderly patients.
Keywords: aging, bacterial CNS infection, phagocytosis, macrophages, microglia, toll-like receptor, NO, cytokine, chemokine
Schlagwörter: Alter, bakterielle ZNS-Infektion, Phagozytose, Makrophagen, Mikroglia, Toll like-Rezeptor, Stickstoffmonoxid, Chemokin, Zytokin
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