Species differences in [ 125I]interleukin-1 binding in brain, endocrine and immune tissues

Abstract

There were dramatic species differences in the level of [ 125I]recombinant human interleukin-1α ([ 125I]hIL-1α) binding with high levels of binding present in mouse and rabbit tissues, while no specific binding was present in rat and guinea pig tissues. Utilizing [ 125I]hIL-1α, moderate to high levels of specific binding were observed in EL-4 6.1 cells (representative of Type I IL-1 receptors) and in mouse hippocampus, spleen and testis; however, no specific [ 125I]hIL-1α binding was present in Raji cells (representative of Type II IL-1 receptors) and in rat tissues. On the other hand, utilizing [ 125I]hIL-1β, high specific IL-1 binding was present in EL-4 6.1 and Raji cells and moderate binding was evident in mouse tissues, whereas specific [ 125I]hIL-1β binding to rat tissues was not detectable. Moreover, no IL-1 binding in rat tissues was observed using [ 125I]hIL-1 receptor antagonist, [ 125I]mouse IL-1β or the homologous radioligands [ 125I]rat IL-1β or [ 125I]rat IL-1 receptor antagonist. These data demonstrate that under optimal conditions for labeling Type I or Type II IL-1 receptors, no specific binding is observed in rat tissues suggesting the presence of novel IL-1 receptor(s) in rat tissues.