Abstract
Olfactory ensheathing cells (OECs) are a type of specialized glial cell currently considered as having a double function in the nervous system: one regenerative, and another immune. Streptococcus pneumoniae is a major agent of severe infections in humans, including meningitis. It is commonly found in the nasopharynx of asymptomatic carriers, and, under certain still unknown conditions, can invade the brain. We evaluated whether pneumococcal cells recovered from lysed OECs and microglia are able to survive by manipulating the host cell activation. An intracellular-survival assay of S. pneumoniae in OECs showed a significant number of bacterial CFU recovered after 3 h of infection. In contrast, microglia assays resulted in a reduced number of CFU. Electron-microscopy analysis revealed a large number of pneumococci with apparently intact morphology. However, microglia cells showed endocytic vesicles containing only bacterial cell debris. Infection of OEC cultures resulted in continuous NF-κB activation. The IFN-γ-induced increase of iNOS expression was reversed in infected OECs. OECs are susceptible to S. pneumoniae infection, which can suppress their cytotoxic mechanisms in order to survive. We suggest that, in contrast to microglia, OECs might serve as safe targets for pneumococci, providing a more stable environment for evasion of the immune system.
Highlights
IntroductionRecent data from our group confirmed these findings, by detecting S. pneumoniae DNA in the olfactory bulb (OB) of bacteria-challenged mice[11]
In opposition to other reports, our data revealed that Olfactory ensheathing cells (OECs) infected with S. pneumoniae for a period of 3 h showed an apparent reduction of inducible nitric oxide synthase (iNOS) levels compared to uninfected OECs
Our results suggest that S. pneumoniae may negatively regulate iNOS, allowing the establishment of infection
Summary
Recent data from our group confirmed these findings, by detecting S. pneumoniae DNA in the OB of bacteria-challenged mice[11]. Several lines of evidence indicate that S. pneumoniae reaches the OB, based on the use of molecular techniques for the detection of bacterial DNA and specific pneumococcal antigens, no data are available to support the idea that the bacteria can survive in the OB cells and be able to spread the infection through the CNS. We evaluated whether pneumococci recovered from lysed OECs and from microglia cells are able to survive by manipulating the host cell to favor their continuity in a less-hostile environment
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