Interleukin-13 is a cytokine which is secreted by activated T lymphocytes and primarily impacts monocytes, macrophages, and B cells. Interleukin 13 is a single-chain glycosylated polypeptide, which belongs to the IL-13/IL-4 family. IL-13 induces its effects through a multi-subunit receptor that includes the alpha chain of the IL-4 receptor （IL-4Rα） and at least one of two known IL-13-specific binding chains. Recent studies have shown that human interleukin-13 has many structural similarities with human interleukin-4 and is produced by gene replication events. As a cytokine, IL-13 protein is critical in regulating inflammatory, immune responses, and diseases. Also, it inhibits the production of pro-inflammatory cytokines and chemokines, and thus down-regulates macrophage activity.