COMPARISON OF PEPTIDOGLYCAN-POLYSACCHARIDE AND LIPOPOLYSACCHARIDE STIMULATION OF KUPFFER CELLS TO PRODUCE TUMOR-NECROSIS-FACTOR AND INTERLEUKIN-1

Endotoxin (lipopolysaccharide) is a cell wall polymer from gram-negati ve bacteria that stimulates Kupffer cell release of cytokines such as tumor necrosis factor-alpha and interleukin-1. Another bacterial cell wall polymer in both gram-negative and gram-positive organisms is pept idoglycan-polysaccharide. Lipopolysaccharide and peptidoglycan-polysac charide exist together in the intestinal lumen and can cross the intes tinal mucosa, enter the portal vein and activate Kupffer cells. The pu rpose of this study was to compare the effects of lipopolysaccharide s timulation and peptidoglycan-polysaccharide stimulation of Kupffer cel ls on release of tumor necrosis factor-alpha and interleukin-1. Both b acterial polymers caused maximum tumor necrosis factor-alpha release f rom Kupffer cells after incubation for 4 to 8 hr. Maximum tumor necros is factor-alpha release induced by 400 ng/ml lipopolysaccharide was 70 4 +/- 258 pg/ml, compared with 329 +/- 91 pg/ml tumor necrosis factor- alpha after 100 mug/ml peptidoglycan-polysaccharide (p < 0.001). Polym yxin B blocked lipopolysaccharide stimulation of tumor necrosis factor -alpha by 95% +/- 5% but blocked peptidoglycan-polysaccharide-stimulat ed tumor necrosis factor-alpha by 30% +/- 14% (p < 0.001). Repeat incu bation of Kupffer cells with lipopolysaccharide after prior lipopolysa ccharide incubation induced low tumor necrosis factor-alpha release (t olerance). Repeat incubation with peptidoglycanpolysaccharide induced no tolerance to tumor necrosis factor-alpha release. Incubation of lip opolysaccharide plus peptidoglycan-polysaccharide released less tumor necrosis factor-alpha than did each polymer used alone, but this inhib ition was prevented by indomethacin. Dibutyryl cyclic AMP, prostagland in E1, prostaglandin E2 and the adenosine A2-receptor agonist N-ethylc arboxyamideadenosine inhibited lipopolysaccharide-stimulated tumor nec rosis factor-alpha release by 83%, 97%, 90% and 94%, respectively, but inhibited peptidoglycanpolysaccharide-stimulated tumor necrosis facto r-alpha release by 52%, 60%, 45% and 51%, respectively (p < 0.001 for each). This indicates that intracellular signaling pathways differ for lipopolysaccharide-stimulated and peptidoglycan-polysaccharide-stimul ated tumor necrosis factor-alpha release. After incubation for 8 and 2 4 hr, 100 mug/ml peptidoglycan-polysaccharide had induced significantl y more interleukin-1 release from cultured Kupffer cells than had 400 ng/ml lipopolysaccharide (p < 0.001). Lipopolysaccharide induced toler ance to interleukin-1 release after repeat incubation, but peptidoglyc an-polysaccharide caused no tolerance. These studies show that peptido glycanpolysaccharide, a ubiquitous bacterial cell wall polymer, shares several proinflammatory properties with lipopolysaccharide but that t here are differences that may have pathophysiological significance.