Induction of tolerance to hemorrhagic or endotoxic shock involves activation of NF-kappa B

Background. Tolerance to hemorrhagic or endotoxic shock can be induced by p rior sublethal hemorrhage (SLH). The purpose of this study was to explore w hether alterations in signal transduction pathways involving NF-kappa B occ ur in macrophages (M phi) following induction of tolerance by SLH. Methods. Using a model of SLH previously shown in our lab to impart a survi val benefit to subsequent hemorrhagic or endotoxic shock, rats (n = 30) wer e conditioned by SLH. Peritoneal M phi were harvested 24 h after conditioni ng and stimulated with lipopolysaccharide (LPS) (10 mu g/mL). Nuclear and c ytosolic proteins were isolated 1 h later for determination of NF-kappa B a ctivation by gel-shift assay and I kappa B-alpha by Western blot. TNF mRNA gene expression was measured 4 h after LPS stimulation by reverse transcrip tion/polymerase chain reaction (RT/PCR), TNF protein levels were measured i n cellular supernatants by enzyme-linked immunosorbent assay (ELISA) 18 h a fter LPS. Results. LPS stimulation of sham M phi increased NF-kappa B activation with corresponding loss of its inhibitor I kappa B-alpha. In contrast, I kappa B-alpha was not detectable following conditioning, and conditioned M phi ha d NF-kappa B activation at baseline which increased minimally with LPS stim ulation. LPS increased TNF gene expression and significantly increased prot ein production by both sham and conditioned M phi, but this increase was gr eater in the sham-conditioned group. Conclusions. The ability of M phi from animals made tolerant by SLH to prod uce TNF in vitro is conserved. Nevertheless, these same M phi exhibit alter ations in TNF gene induction and expression as well as signal transduction, specifically, changes in I kappa B-alpha and NF-kappa B activation. This s uggests a role for activation of NF-kappa B in the induction of tolerance. (C) 1999 Academic Press.