Cloning and Characterization of Two Toll/Interleukin-1 Receptor–Like Genes TIL3 and TIL4: Evidence for a Multi-Gene Receptor Family in Humans

Remarkable structural and functional similarities exist between the Drosophila Toll/Cactus/Dorsal signaling pathway and the mammalian cytokine-mediated interleukin-1 receptor (IL-1R)/I-kappaB/NF-kappaB activation cascade. In addition to a role regulating dorsal-ventral polarity in the developing Drosophila embryo, signaling through Drosophila Toll (dToll) activates the nonclonal, or innate, immune response in the adult fly. Recent evidence indicates that a human homologue of the dToll protein participates in the regulation of both innate and adaptive human immunity through the activation of NF-kappaB and the expression of the NF-kappaB-controlled genes IL-1, IL-6, and IL-8, thus affirming the evolutionary conservation of this host defense pathway. We report here the cloning of two novel human genes, TIL3 and TIL4 (Toll/IL-1R-like-3, -4) that exhibit homology to both the leucine-rich repeat extracellular domains and the IL-1R-like intracellular domains of human and Drosophila Toll. Northern analysis showed distinctly different tissue distribution patterns with TIL3 expressed predominantly in ovary, peripheral blood leukocytes, and prostate, and TIL4 expressed primarily in peripheral blood leukocytes and spleen. Chromosomal mapping by fluorescence in situ hybridization localized the TIL3 gene to chromosome 1q41-42 and TIL4 to chromosome 4q31.3-32. Functional studies showed that both TIL3 and TIL4 are able to activate NF-kappaB, though in a cell type-dependent fashion. Together with human Toll, TIL3 and TIL4 encode a family of genes with conserved structural and functional features involved in immune modulation.