IL-10 and IL-4 regulate type-I and type-II IL-1 receptors expression on IL-1 beta-activated mouse primary astrocytes

When activated by its ligand, the interleukin receptor type I (IL-1RI) tran sduces signals in cooperation with the IL-1 receptor accessory protein (IL- 1 RacP). In contrast, IL-1RII functions as a decoy receptor without partici pating in IL-1 signalling. Brain astrocytes are cellular targets of IL-1 an d play a pivotal role in brain responses to inflammation. The regulation of IL-1 receptors on astrocytes by anti-inflammatory cytokines such as IL-4 a nd IL-10 has not been studied, despite its importance for understanding the way these cells respond to IL-1. Using RT-PCR, we first showed that the ex pression of IL-1RI and IL-1RII, but not IL-1RacP, mRNAs are up-regulated by IL-1 beta in a time-dependent manner. Using a radioligand binding techniqu e, we then showed that astrocytes display an equivalent number of IL-1RI an d IL-1RII. IL-1 beta decreases the number of IL-1RI binding sites, whereas it increases those of IL-1RII. IL-4 and IL-10 both up-regulate IL-1RII IL-1 beta -induced, but only IL-4 does so for IL-1RI. At the protein level, IL- 4 and IL-10 dramatically reverse the ability of IL-1 beta to inhibit expres sion of IL-1RI but neither affects the ability of IL-1 beta to enhance the number of IL-1RII. Collectively, these results establish the existence of r eceptor cross-talk between pro- and anti-inflammatory cytokines on a critic al type of cell that regulates inflammatory events in the brain.