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Keywords:

  • interleukin 1 receptors;
  • interleukin 1 signaling;
  • microglial cells;
  • mitogen-activated protein kinase;
  • nuclear factor kappa B

Abstract

Interleukin (IL)-1 is an important mediator of acute brain injury and inflammation, and has been implicated in chronic neurodegeneration. The main source of IL-1 in the CNS is microglial cells, which have also been suggested as targets for its action. However, no data exist demonstrating expression of IL-1 receptors [IL-1 type-I receptor (IL-1RI), IL-1 type-II receptor (IL-1RII) and IL-1 receptor accessory protein (IL-1RAcP)] on microglia. In the present study we investigated whether microglia express IL-1 receptors and whether they present target or modulatory properties for IL-1 actions. RT–PCR analysis demonstrated lower expression of IL-1RI and higher expression of IL-1RII mRNAs in mouse microglial cultures compared with mixed glial or pure astrocyte cultures. Bacterial lipopolysaccharide (LPS) caused increased expression of IL-1RI, IL-1RII and IL-1RAcP mRNAs, induced the release of IL-1β, IL-6 and prostaglandin-E2 (PGE2), and activated nuclear factor κB (NF-κB) and the mitogen-activated protein kinases (MAPKs) p38, and extracellular signal-regulated protein kinase (ERK1/2), but not c-Jun N-terminal kinase (JNK) in microglial cultures. In comparison, IL-1β induced the release of PGE2, IL-6 and activated NF-κB, p38, JNK and ERK1/2 in mixed glial cultures, but failed to induce any of these responses in microglial cell cultures. IL-1β also failed to affect LPS-primed microglial cells. Interestingly, a neutralizing antibody to IL-1RII significantly increased the concentration of IL-1β in the medium of LPS-treated microglia and exacerbated the IL-1β-induced IL-6 release in mixed glia, providing the first evidence that microglial IL-1RII regulates IL-1β actions by binding excess levels of this cytokine during brain inflammation.