Differential expression of cytokines in the brain and serum during endotoxin tolerance.

Using short- and long-course lipopolysaccharide (LPS) treatment regimens to induce endotoxin tolerance in rats, we compared TNF-alpha, IL-1beta, and IL-6 expression in the brain and serum following a LPS challenge. Serum corticosterone was also examined to evaluate the function of the hypothalamic-pituitary-adrenal (HPA) axis. We found that, during endotoxin tolerance, LPS-induced cytokine expression still occurred in the brain even when cytokines in the periphery were no longer induced, and that this differential cytokine expression may be mediated by corticosterone, a stress hormone and an anti-inflammatory agent.