Bacterial lipoprotein induces endotoxin‐independent tolerance to the systemic inflammatory response syndrome in vivo and in vitro

Background Sublethal doses of endotoxin (lipopolysaccharide; LPS) induce tolerance in vivo and in vitro , and protect against the lethal effects of a further LPS challenge. Tolerance is characterized by diminished production of tumour necrosis factor (TNF) α. Bacterial lipoprotein (BLP), another bacterial wall component, might induce tolerance against its own lethal effects as well as those of endotoxin. Methods Ninety male MF‐1 mice (mean(s.d.) weight 18(2) g) were randomized into three groups ( n = 30 per group). Mice in group 1 received a single BLP‐tolerant dose (10 mg kg −1 ) by intraperitoneal injection, whereas mice in group 2 received a second BLP‐tolerant dose (10 mg kg −1 ) after 24 h. Following induction of tolerance, all mice were challenged with high doses of LPS 45 mg kg −1 , BLP 45 mg kg −1 or a combination of LPS 30 mg kg −1 plus BLP 30 mg kg −1 . Mice in group 3 were treated with a high dose of the above agents only. Mortality was assessed at 24 and 48 h. Macrophages were isolated from mice and pretreated in vitro with culture medium alone or culture medium containing LPS 10 ng ml −1 or BLP 10 ng ml −1 for 24 h. The cells were then stimulated with high doses (100–1000 ng ml −1 ) of LPS, BLP or LPS plus BLP for 6 h. The cell culture supernatants were collected and TNF‐α levels were determined using enzyme‐linked immunosorbent assay. Results BLP‐induced tolerance significantly improved survival compared with that of mice without tolerance ( P < 0·05). In vitro , pretreatment of murine macrophages with BLP significantly attenuated LPS, BLP and LPS plus BLP stimulation‐induced TNF‐α production.Mortality rate LPS 45 mg kg −1 BLP 45 mg kg −1 LPS 30 mg kg −1 + BLP 30 mg kg −124 h 48 h 24 h 48 h 24 h 48 hNo tolerance 80 80 60 60 60 80 Single tolerance 40 * 40 * 0 * 0 * 0 * 0 * Repeat tolerance 20 * 30 * 0 * 0 * 0 * 0 ** P < 0·05 versus mice without tolerance (log rank test)Conclusion BLP mimics LPS in the development of the systemic inflammatory response syndrome. Furthermore, BLP is capable of inducing tolerance, both in vivo and in vitro , which subsequently prevents BLP‐ and LPS plus BLP‐induced death. © 2000 British Journal of Surgery Society Ltd