Pattern of IL-1 receptor gene expression suggests role in noninflammatory processes

The cytokine IL-1 can be elaborated by most nucleated cell types and exerts its pleiotropic effects on a variety of tissues through binding to its cognate receptor. Two forms of IL-1R, designated types I and II, have been identified. These proteins share limited amino acid identity but both bind IL-1 alpha and IL-1 beta. A large number of cell types have been shown to possess IL-1R in vitro, but few studies have addressed the question of in vivo expression. Using in situ hybridization in normal adult BALB/c mice, we have examined the tissue distributions of both IL-1R types. The results demonstrate that although lymphoid tissues in healthy animals express low or nondetectable levels of receptor transcript, nonlymphoid tissues constitutively express readily detectable levels of IL-1R mRNA. Thymus and spleen samples were largely negative for both IL-1R types I and II, whereas half of the lymph nodes examined expressed IL-1R type I. In nonlymphoid tissues, IL-1R type I transcript was detected in the dentate gyrus of the brain, endocrine pancreas, cardiac endothelium, epidermis, dermis, hair follicle epithelium, uterine serosa, vaginal stroma, vaginal squamous epithelium, developing oocytes, and granulosa cells of ruptured follicles. In contrast, the IL-1R type II probe hybridized to epidermis, dermis, and vaginal basal epithelium. The two types of IL-1R were rarely, if ever, co-expressed by the same cell. The distributional segregation of the receptor types and the expression of IL-1R in normal nonlymphoid tissues has broad implications for the role of IL-1 in homeostatic physiology.