Janus kinase 3

Janus kinase 3 (a protein tyrosine kinase, leukocyte), also known as JAK3, is a human gene.

Since JAK3 expression is restricted mostly to hematopoietic cells, its role in cytokine signaling is thought to be more restricted than other JAKs. It is most commonly expressed in T cells and NK cells, but has been induced in other leukocytes, including monocytes. Jak3 is involved in signal transduction by receptors that employ the common gamma chain (γC) of the type I cytokine receptor family (e.g. IL-2R, IL-4R, IL-7R, IL-9R, IL-15R, and IL-21R). Mutations of JAK3 result in severe combined immunodeficiency (SCID). Mice that do not express JAK3 have T-cells and B-cells that fail to respond to many cytokines.