Acta path. microbiol. immunol. scand. Sect. B, 95: 135-139, 1987. TOXIC EFFECTS OF LIPOPOLYSACCHARIDE FROM zy BACTEROIDES INTEMEDIUS AND ESCHERICHIA COLI ASSESSED IN THE PRE-IMPLANTATION MOUSE EMBRYO CULTURE SYSTEM RITSA STORENG' and BERIT JOHNE2 'The Norwegian Radium Hospital, Oslo and *Department of Microbiology, Dental Faculty, University of Oslo, Blindern, Oslo 3, Norway Storeng, R. zyxwvutsrq & Johne, B. Toxic effects of lipopolysaccharides from Bacteroides intermedius and zy Es- clierichia coli, assessed in the pre-implantation mouse embryo culture system. Acta path. microbiol. im- munol. scand. Sect. B, zyxwvut 95: 135-139, 1987. A comparative study on the toxic effects of endotoxin (lipopolysaccharide, LPS) from the strictly anaero- bic Bacleroides intermedius BMI and. from Escherichia coli 055 was performed. Pre-implantation mouse embryos at the 2-cell stage from LPS responder (C57BL/6J) and low responder (C3H/Hej) mouse strrains were exposed to the endotoxins, and development was observed during 72 h in vitro. Toxic effects of both endotoxins on embryos from both mouse strains were demonstrated. B. intermedius LPS was less toxic than E. coli LPS. The C3H/HeJ embryos were more susceptible to endotoxins than the C57BL/6J em- bryos. A biphasic dose-response relationship was observed, as 100 pg/ml LPS was less embryotoxic than I, 10 or 500 pg/ml, suggesting more complex mechanisms of effect than non-specific cell toxicity. Key words: Endotoxin; Bacferoides intermedius; Escherichia coli; pre-implantation mouse embryo; toxicity. Bent Johne, Department of Microbiology, Dental Faculty, University of Oslo, Blindern, Oslo 3, Norway. Received I8.ix.86 Accepted 7.xi.86 Endotoxins (lipopolysaccharides, zyxwvu LPSs) from Gram-negative bacteria exert multiple biological effects (7). They are important factors in the pathogenesis and development of Gram-negative infections (14, 15). On the other hand, beneficial effects of bacterial endotoxins are immunodulato- ry activity and enhancement of non-specific resis- tance to microbial infections zyxwvu (1 1). Endotoxic effeqts are linked to the lipid A part of the LPS molecule (7) and may be divided into toxic effects and immunomodulatory activity (4). At present, substantial interest is focused on syn- thetic lipid A analogues with low toxicity, but complete immunodulatory properties (6), for fu- ture therapeutic use as enhancers of non-specific resistance to infections. In a previous study (2) Bacteroides intermedius LPS was characterized as to chemical composition and biological activity. We found that it was nota- bly less toxic than E. coli LPS in biological tests (Shwartzman reaction, mouse lethality, chick em- bryo lethality) where the immune system and the reticulo-endothelial system of the animal are im- portant mediators of the detrimental effects (8, 16). The aim of the present study was to compare toxic effects of two structurally different endotox- ins in a complex biological system free from im- munocompetent cells. he-implantation embryo cultures constitute a well-established and suitable in vitro system for such toxicity testing (10, 17, 18, 19, 20). In a previous study (submitted for publication) 135