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Heat-killed pneumococci and pneumococcal capsular polysaccharides stimulate tumor necrosis factor-alpha production by
S Q Simpson1, R Singh, D E Bice
1Department of Medicine, University of New Mexico, Albuquerque 87131-5271.
Abstract:
Tumor necrosis factor-alpha (TNF) is an important humoral mediator of sepsis and endotoxin-induced shock. However, Streptococcus pneumoniae, a gram-positive organism, is the most common causative agent of community-acquired pneumonia and sepsis. We hypothesized that the pathogenesis of pneumococcal pneumonia and sepsis involves pneumococcus-stimulated TNF synthesis, and we tested that hypothesis in vitro by comparing heat-killed type III and type V pneumococcus and 23-valent purified pneumococcal capsular polysaccharides with Escherichia coli and purified lipopolysaccharide (LPS) as stimuli for TNF production by the murine macrophage cell line RAW 264.7. We evaluated TNF production in response to various doses and times of exposure to these agents, as well as the effects of indomethacin on TNF production in response to these agents. Stimulation with both types of heat-killed pneumococcus resulted in TNF production in a dose-response fashion, as did stimulation with E. coli. Fewer type III pneumococci (10 bacteria/ml) were required to stimulate significant TNF secretion than either type V pneumococcus or E. coli, but the overall dose-response curves of the three bacteria were similar. The dose-response curves for pneumococcal capsular polysaccharides and LPS were very similar, although at the highest concentration pneumococcal capsular polysaccharides stimulated more TNF secretion than did LPS (469 versus 213 U/ml). The kinetics of pneumococcus-stimulated TNF secretion were identical to the kinetics of LPS-stimulated TNF secretion. In the presence of indomethacin, pneumococcus-stimulated TNF production decreased by 87.5%, as compared with pneumococcus alone. In contrast, LPS with indomethacin stimulated 19.5% more TNF than LPS alone.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Streptococcus pneumoniae stimulates tumor necrosis factor-alpha (TNF) production in macrophages, similar to lipopolysaccharide (LPS). Indomethacin inhibits pneumococcus-induced TNF but enhances LPS-induced TNF, suggesting distinct pathways in sepsis pathogenesis.
Area of Science:
- Immunology
- Microbiology
- Pathogenesis
Background:
- Sepsis and endotoxin-induced shock involve tumor necrosis factor-alpha (TNF).
- Streptococcus pneumoniae is a common cause of pneumonia and sepsis.
- The role of pneumococcus in TNF synthesis during sepsis is not fully understood.
Purpose of the Study:
- To investigate whether Streptococcus pneumoniae stimulates TNF production in macrophages.
- To compare the TNF-inducing capacity of pneumococci and their capsular polysaccharides with Escherichia coli and lipopolysaccharide (LPS).
- To examine the effect of indomethacin on TNF production induced by pneumococci and LPS.
Main Methods:
- Murine macrophage cell line RAW 264.7 was stimulated with heat-killed pneumococci (types III and V), pneumococcal capsular polysaccharides, E. coli, and LPS.
- TNF production was evaluated at various doses and exposure times.
- The effect of indomethacin on TNF production was assessed.
Main Results:
- Both heat-killed pneumococci and E. coli stimulated TNF production in a dose-dependent manner.
- Pneumococcal capsular polysaccharides and LPS exhibited similar dose-response curves for TNF induction.
- Indomethacin significantly decreased pneumococcus-stimulated TNF production but increased LPS-stimulated TNF production.
Conclusions:
- Streptococcus pneumoniae actively stimulates TNF synthesis in macrophages.
- Pneumococcal capsular polysaccharides are potent inducers of TNF, comparable to LPS.
- The differential effect of indomethacin suggests distinct mechanisms in TNF regulation by pneumococci and LPS during sepsis.