Pneumococcal cell wall components induce nitric oxide synthase and TNF-α in astroglial-enriched cultures

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Abstract
Astroglia and microglia, the most numerous cells in the central nervous system (CNS), have been shown to produce the inducible nitric oxide synthase (iNOS) and tumor necrosis factor-α (TNF-α) upon stimulation with the cytokines IFN-γ, IL-1β, or bacterial lipopolysaccharides (LPS). However, it is not known whether gram-positive bacteria like Streptococcus pneumoniae cause astroglial cells to release nitric oxide (NO) and TNF-α. S. pneumoniae meningitis still has a high incidence and mortality in spite of antibiotic therapy. Cell wall components from S. pneumoniae (pneumococcal cell-wall components, PCW) and TNF-α have been shown to cause meningeal inflammation and cerebrovascular changes in experimental meningitis. Addition of PCW to cultured rat astroglial cells increased nitrite in the supernatant significantly after 24 h, from 17 ± 21 to 133 ± 62 nM/μg protein. Nitrite release was dose-dependent in a range shown to cause meningeal inflammation in vivo and was inhibited by the competitive NO synthase inhibitor NW-nitro-L-arginine (L-NA 10−4 M) and dexamethasone (10−6 M), with transcriptional and translational inhibition by actinomycin D and cycloheximide, respectively. PCW caused a significant increase in the release of TNF-α from astroglial cells after 4 h, from 2 ± 3.5 pg/ml to 102 ± 13.5 pg/ml, which was inhibited by dexamethasone (10−6 M). Our results suggest a role for astroglial-derived NO and TNF-α as mediators of vascular and inflammatory response in the early phase of experimental pneumococcal meningitis.