Human IL-13 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 IL-13 (P600) cDNA as a probe. Human IL-13, a pleiotropic cytokine, is produced by activated Th0, Th1 like, Th2 like, and CD8 T cells. The gene for human IL-13 maps to chromosome 5 and is closely linked to the genes for IL3, IL4, IL5, and GMCSF. IL-13 inhibits proinflammatory cytokine production and stimulates antibody production. It induces proliferation in the human pre myeloid cell line TF1. IL-13 has multiple effects on the differentiation and functions of monocytes and macrophages. It suppresses cytotoxic functions and induces changes in the morphology of human monocytes and in the phenotype of human monocytes and B cells by upregulating MHC class II expression. IL-13 will also decrease the production of nitric oxide by activated murine macrophages, leading to impaired parasiticidal activity. Human and mouse interleukin 13 share approximately 58% amino acid sequence identity. Although human and mouse IL-13 are equally active on human cells, human IL-13 is much less active than mouse IL-13 on mouse cells. Human IL-13 and human IL-4 also share approximately 30% sequence homology and have similar biological functions.

Secreted