Heat-killed pneumococci and pneumococcal capsular polysaccharides stimulate tumor necrosis factor-alpha production by murine macrophages.

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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)

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