Role of IL-1RAcP and IL-1ra in IL-1 signalling : molecular biological and transgenic studies

Sammanfattning: IL-1 is a proinflammatory cytokine which causes systemic responses such as fever, increased neuroendocrine activity, sympathetic outflow and increased immune responses. Activation of the transcription factor NFkB is one of the molecular mechanisms involved in IL-1 signalling.We have shown that the IL-1binduced fever response is regulated the hypothalamic - pituitary - adrenal axis (HPA-axis), as either the nonpeptidic CRF receptor antagonist CP154,526, or a subchronic glucocorticoid treatment, respectively, blocked the ability of peripheral IL-1bto induce fever in rats. The subchronic glucocorticoid treatment caused a dampened IL-1aand IL-1bmRNA expression in the hypothalamus whereas IL-6 mRNA was induced by the same glucocorticoid treatment. Both the glucocorticoid altered cytokine mRNA levels and IL-1 induced fever responses, respectively, were reversed to normal upon the removal of exogenous glucocorticoids. Both IL-1 receptor antagonist (IL-1ra) mRNA and protein were detectable in adrenal chromaffin cells. Adrenal IL-1ra mRNA levels were furthermore rapidly induced by a peripheral lipopolysaccharide (LPS) challenge.Type II IL-1R (IL-1RII) is a negative regulator of IL-1 bioactivities by being a nonsignaling, IL-1 binding protein. Here we present evidence that IL-1RII also can interact with IL-1R accessory protein (IL-1RAcP), thus extending the previously known IL-1 suppressing activity of IL-1RII to encompass the sequestering of IL-1RAcP from the signaling IL-1RI complex. IL-1RAcP was shown to be a necessary component of the murine (m) IL-1RI complex in transducing the IL-1 signal to NFkB activation in murine fibroblast C127 cells and in primary mouse astrocyte cultures. In addition, heterologous murine IL-1RAcP and human IL-1RI complexes formed functional IL-1bsignaling complexes.Transgenic mice deficient in IL-RAcP did not respond with fever to either a peripheral injection of IL-1aor to IL-1b, thus implicating IL-1RAcP as a necessary component of the IL-1RI complex in vivo.To examine the role of central IL-1ra in suppressing IL-1signaling, the cDNA encoding the human secretable form of IL-1ra (hsIL-1ra) was expressed under the control of the glia fibrillary acidic protein (GFAP) promoter in transgenic mice. The expression of hsIL-1ra mRNA and protein were exclusively restricted to CNS, as measured by RT-PCR and ELISA, respectively. The GFAP-hsIL-1ra (GILRA) mice did not exhibit fever upon a central injection of IL-1b, while a peripheral LPS injection caused a hypersensitive fever response in these mice. These mice strains provide a model for studies on IL-1R occupancy and systemic responses.