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

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. © 1996 Wiley‐Liss, Inc.

Cell Wall-Mediated Neuronal Damage in Early Sepsis

“…Inflammation driven by intravascular cell wall appeared to participate in SAND. Although cell wall is known to induce cellular activation and cytokine production (13,14), cell wallchallenged animals produced very low amounts of systemic and CSF cytokines at the time of peak SAND. The persistence of SAND in mice treated with anti-TNF antibody further argued against classical cytokine-mediated damage.…”

“…For example, in the meningitis model, the capsule was poorly inflammatory while choline-bearing, insoluble cell wall was strongly inflammatory. Removal of choline teichoic acid from peptidoglycan yielded a more restricted array of bioactivities, digestion further to muramyl peptides more strongly limited inflammatory capability, and cleavage of stem peptides virtually eliminated bioactivity (6,14,27,46,48,53). More recently, distinct molecules involved in recognition of these different cell wall subspecies have been described: TLR2 participates in the inflammatory responses of peptidoglycan while Nod2 appears to recognize the smaller, muramyl peptides (16,55).…”

Tyrosine Kinase Inhibition Reduces Inflammation in the Acute Stage of Experimental Pneumococcal Meningitis

“…Clinically, increased ICP in the acute phase of bacterial meningitis is enormously important and may be attributed to at least three mechanisms (21): (i) vasogenic edema due to extravasation of plasma compounds and hyperemia; (ii) cytotoxic edema caused by toxins released from activated leukocytes (13), glia (20), endothelial cells (12), and bacteria; and (iii) an increase in CSF outflow resistance (22). Decreased ICP in tyrphostin-treated animals may result from attenuated hyperemia, as well as reduced leukocyte recruitment and TNF-␣ concentrations in the CSF.…”

Pathogenesis and Pathophysiology of Pneumococcal Meningitis

“…Several cells have been found to be capable of sensing pneumococci and produce proinflammatory cytokines: perivascular and meningeal macrophages (393,557), vascular endothelial cells (153), astrocytes (154), and microglial cells (193,413). These early-phase cytokines induce upregulation of several adhesion factors on the vascular endothelium, mediating leukocyte influx (see above) (142,470).…”