PNEUMOCOCCAL CELL-WALL COMPONENTS INDUCE NITRIC-OXIDE SYNTHASE AND TNF-ALPHA - IN ASTROGLIAL-ENRICHED CULTURES

Astroglia and microglia, the most numerous cells in the central nervou s system (CNS), have been shown to produce the inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) upon stimu lation with the cytokines IFN-gamma, IL-1 beta, or bacterial lipopolys accharides (LPS). However, it is not known whether gram-positive bacte ria like Streptococcus pneumoniae cause astroglial cells to release ni tric oxide (NO) and TNF-alpha. S. pneumoniae meningitis still has a hi gh incidence and mortality in spite of antibiotic therapy. Cell wall c omponents from S. pneumoniae (pneumococcal cell-wall components, PCW) and TNF-alpha have been shown to cause meningeal inflammation and cere brovascular changes in experimental meningitis. Addition of PCW to cul tured rat astroglial cells increased nitrite in the supernatant signif icantly after 24 h, from 17 +/- 21 to 133 +/- 62 mM/mu g protein. Nitr ite release was dose-dependent in a range shown to cause meningeal inf lammation in vivo and was inhibited by the competitive NO synthase inh ibitor N-W-nitro-L-arginine (L-NA 10(-4)M) and dexamethasone (10(-6)M) , with transcriptional and translational inhibition by actinomycin D a nd cycloheximide, respectively. PCW caused a significant increase in t he release of TNF-alpha from astroglial cells after 4 h, from 2 +/- 3. 5 pg/ml to 102 +/- 13.5 pg/ml, which was inhibited by dexamethasone (1 0(-6)M). Our results suggest a role for astroglial-derived NO and TNF- a as mediators of vascular and inflammatory response in the early phas e of experimental pneumococcal meningitis. (C) 1996 Wiley-Liss, Inc.