HEAT-KILLED PNEUMOCOCCI AND PNEUMOCOCCAL CAPSULAR POLYSACCHARIDES STIMULATE TUMOR-NECROSIS-FACTOR-ALPHA PRODUCTION BY MURINE MACROPHAGES

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 commu nity-acquired pneumonia and sepsis. We hypothesized that the pathogene sis of pneumococcal pneumonia and sepsis involves pneumococcus-stimula ted TNF synthesis, and we tested that hypothesis in vitro by comparing heat-killed type III and type V pneumococcus and 23-valent purified p neumococcal capsular polysaccharides with Escherichia coli and purifie d lipopolysaccharide (LPS) as stimuli for TNF production by the murine macrophage cell line RAW 264.7. We evaluated TNF production in respon se to various doses and times of exposure to these agents, as well as the effects of indomethacin on TNF production in response to these age nts. 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 w ere similar. The dose-response curves for pneumococcal capsular polysa ccharides and LPS were very similar, although at the highest concentra tion pneumococcal capsular polysaccharides stimulated more TNF secreti on than did LPS (469 versus 213 U/ml). The kinetics of pneumococcus-st imulated TNF secretion were identical to the kinetics of LPS-stimulate d TNF secretion. In the presence of indomethacin, pneumococcus-stimula ted TNF production decreased by 87.5%, as compared with pneumococcus a lone. In contrast, LPS with indomethacin stimulated 19.5% more TNF tha n LPS alone. These data indicate that heat-killed pneumococci and puri fied pneumococcal capsular polysaccharides stimulate TNF synthesis and secretion by murine macrophages at least as potently as E. coli and p urified LPS, respectively, and that pneumococci stimulate TNF producti on by different mechanisms than LPS, perhaps involving prostaglandins in a different manner than LPS-stimulated TNF secretion.