Evolution of interleukin-18 binding protein

Motivation: Interleukin-18 (IL-18) is one of the pivotal cytokines, which controls,defense mechanism called inflammation. To develop proteins available for controlling the local and/or circulating IL-18 levels, we initiated study of interleukin-18 binding proteins (IL-18BPs). Results: Eighteen IL-18BPs, 7 from vertebrates and I I from chordopoxviruses, were picked from the NCBI database. All of their IL-18 binding domains (IL-18BDs) were aligned and a phylogenetic tree constructed. Our results suggested that at least two independent events created two different ancestral viral IL-18BP genes by retroposing IL-18BP genes from the vertebrate lineage. These two events are estimated to have occurred, after an ancient mammalian IL-18BP gene diverged from bird, and before the mammalian IL-18BP gene diverges into human, ungulate and rodent IL-18BP genes.