PERIPHERAL MACROPHAGE DEPLETION PREVENTS DOWN-REGULATION OF CENTRAL INTERLEUKIN-1 RECEPTORS IN MICE AFTER ENDOTOXIN ADMINISTRATION

Interleukin-1 receptors (IL-1R) have been characterized in the brain a nd pituitary gland of mice. Previous studies have demonstrated that fo llowing lipopolisaccharide (LPS) injection, IL-1R density decreases in the dentate gyrus and in the choroid plexus. Receptors present in the anterior pituitary gland remain unchanged under the same experimental conditions. In this study, we investigated the role of peripheral mac rophages in LPS-induced downregulation of IL-1 receptors. Mice were in jected with liposomes encapsulated with dichloromethylene diphosphonat e (Cl(2)MDP), which induced a profound depletion of peripheral macroph ages. Immunocytochemistry was used to determine the efficiency of macr ophage elimination. Depletion of macrophages did not affect the densit y of central and pituitary IL-1R in non-LPS-challenge mice. However, t he liposome treatment prevented downregulation of IL-1R in the dentate gyrus observed following LPS administration. In addition, LPS induced a slight decrease in IL-1R density in the choroid plexus but not in t he anterior pituitary gland of liposome treated mice. These results su ggest that peripheral macrophages play an important role in the LPS-in duced modulation of central IL-1R.