INTERLEUKIN-1 RECEPTORS IN MOUSE-BRAIN - CHARACTERIZATION AND NEURONAL LOCALIZATION

The cytokine interleukin-1 (IL-1) has a variery of effects in brain, including induction of fever, alteration of slow wave sleep, and alteration of neuroendccrine activity. To examine the potential sites of action of IL-1 in brain, we used iodine-125-labeled recombinant human interleukin-1 ([125I]IL- 1) to identify and characterize IL-1 receptors in crude membrane preparations of mouse (C57BL/6) hippocampus and to study the distribution of IL-1-binding sites in brain using autoradiography. In preliminary homogenate binding and autoradiographic studies, [125I]IL-1α showed significantly higher specific binding than [125I]IL-1β. Thus, [125I]IL-1α was used in all subsequent assays. The binding of [125I]IL-1α was linear over a broad range of membrane protein concentrations, saturable, reversible, and of high affinity, with an equilibrium dissociation constant value of 114 ± 35 pM and a maximum number of binding sites of 2.5 ± 0.4 fmol/mg protein. In competition studies, recombinant human IL-1α, recombinant human IL-1β, and a weak IL-1β analog, IL-β+, inhibited [125I]IL-1α binding to mouse hippocampus in parallel with their relative bioactivities in the T-cell comitogenesis assay, with inhibitory binding affinity constants of 55 ± 18, 76 ± 20, and 2940 ± 742 pM, respectively; rat/human CRF and human tumor necrosis factor showed no effect on [125I] IL-1α binding. Autoradiographic localization studies revealed very low densities of [125I]IL-1α-binding sites throughout the brain, with highest densities present in the molecular and granular layers of the dentate gyrus of the hippocampus and in the choroid plexus. Quinolinic acid lesion studies demonstrated that the [125I]IL-1α-binding sites in the hippocampus were localized to intrinsic neurons. After hypophysectomy, homogenate binding and autoradiographic studies showed that there was no apparent change in the relative density of IL-1 receptors in the hippocampus. The identification of IL-1 receptors in brain with characteristics similar to IL-1 receptors in immune and neuroendocrine tissues provides further support for a physiological role for IL-1 to regulate central nervous system activity. © 1990 by The Endocrine Society.