Human IL13 was originally identified by differential screening of an anti CD28 activated human peripheral blood mononuclear cell cDNA library as an induction specific novel cytokine. It was also isolated from cDNA libraries of human T cell clones using the murine IL13 (P600) cDNA as a probe. Human IL13, a pleiotropic cytokine, is produced by activated Th0, Th1 like, Th2 like, and CD8 T cells. The gene for human IL13 maps to chromosome 5 and is closely linked to the genes for IL3, IL4, IL5, ａ