INDUCTION OF RELEASE OF TUMOR-NECROSIS-FACTOR AND IL-6 FROM HUMAN MONONUCLEAR-CELLS BY BACTEROIDES STRAINS

The role of anaerobic Gram-negative bacteria in inducing cytokines dur ing mixed infections involving aerobic and anaerobic bacteria is relat ively poorly defined. The purpose of this study was to establish wheth er or not intact Bacteroides fragilis and related species, isolated fr om severe infections and from the faeces of healthy persons are capabl e of releasing tumor necrosis factor (TNF) and IL-6 from human mononuc lear cells and whole blood. The purified lipopolysaccharides of Bacter oides fragilis strain (No. 7), extracted by the aqueous phenol method from BHI cultures and from BKI culture supplemented with 5% horse seru m, were also tested. TNF release was detected by the WEHI 164-dependen t bioassay and IL-6 production by the B-9 cell-dependent bioassay. Hea t-inactivated Bacteroides strains belonging to different species were able to induce TNF (1 x 10(1)-5 x 10(2)U/mL) and IL-6 (1 x 10(1)-5 x 1 0(5)pg/mL) release from human mononuclear cells. When whole blood was used, the production of TNF and IL-6 was more pronounced (very probabl y because of the presence of certain serum factors). The culturing con ditions (the presence of 5% horse serum in the BHI broth) influenced t he inducing activity of almost all strains tested. The isolated lipopo lysaccharide of Bacteroides fragilis strain No. 7 proved to have a rou gh profile on PAGE. There were no differences in TNF and IL-6 inductio n when the lipopolysaccharides of the strain was cultured in BHI or in BHI supplemented with 5% horse serum. Bacteroides strains often outnu mber Enterobacteriaceae in the faeces and in mixed infections, and the ir role in inducing and/or modulating the host response in septic shoc k should not be overlooked. (C) 1998 Academic Press.