INTERLEUKIN-10 INHIBITS LIPOPOLYSACCHARIDE-INDUCED TUMOR-NECROSIS-FACTOR AND INTERLEUKIN-1-BETA PRODUCTION IN THE BRAIN WITHOUT AFFECTING THE ACTIVATION OF THE HYPOTHALAMUS-PITUITARY-ADRENAL AXIS

Interleukin (IL) 10 inhibits endotoxin (lipopolysaccharide; LPS) induced tumor necrosis factor (TNF) production in vivo and in vitro. In turn, IL-10 is induced by LPS and acts as a negative feedback to limit TNF production. We investigated the effects of IL-10 on brain TNF and IL-1 beta production induced by a central LPS administration in mice. Because central LPS also induces peripheral TNF, we also measured the serum TNF levels. A single intracerebroventricular injection of murine recombinant IL-10 (75 ng/mouse) simultaneously with LPS (2.5 mu g/mouse) almost completely inhibited brain TNF production. The brain IL-1 beta production was also inhibited, as was the serum concentration of the acute-phase protein serum amyloid A. On the other hand, intracerebroventricular administration of an anti-IL-10 monoclonal antibody (JES5-2A5; 60 mu g/mouse) potentiated brain TNF and IL-1 beta production. Identical results were obtained when the serum TNF levels were measured. IL-10 did not affect the LPS-induced increase of serum corticosterone, the main endogenous inhibitor of TNF production, or the induction of IL-6. These results indicate that LPS-induced IL-10 can act as an important endogenous inhibitor of brain TNF production and suggest an anti-inflammatory role for IL-10 in the central nervous system.