SPECIES-DIFFERENCES IN [I-125] INTERLEUKIN-1 BINDING IN BRAIN, ENDOCRINE AND IMMUNE TISSUES

There were dramatic species differences in the level of [I-125]recombinant human interleukin-1alpha ([I-125]hlL-1alpha) 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 [I-125]hIL-1alpha 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 [I-125]hIL-1alpha binding was present in Raji cells (representative of Type II IL-1 receptors) and in rat tissues. On the other hand, utilizing [I-125]hIL-lP, 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 [I-125]hIL-1beta binding to rat tissues was not detectable. Moreover, no IL-1 binding in rat tissues was observed using [I-125]hIL-1 receptor antagonist, (I-125]mouse IL-1beta or the homologous radioligands [I-125]rat IL-1beta or [I-125]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.