The four members of the Janus kinase (Jak) family and the major cytokines reported to activate them
| Jak | Cytokines that activate | Phenotype of knockout* |
|---|---|---|
| *The phenotype associated with deficiency of each of the Jaks is also summarised. | ||
| SCID, severe combined immunodeficiency; IFN, interferon. | ||
| Jak1 | gp130 cytokines, type I IFNs, IFNγ, γc cytokines | Perinatally lethal, neurological defects, SCID |
| Jak2 | Erythropoietin, thrombopoietin, prolactin, growth hormone, βc cytokines,IFNγ, IL-12 | Embryonically lethal, defective erythropoiesis |
| Jak3 | γc cytokines | SCID |
| Tyk2 | gp130 cytokines, type I IFNs, IL-12, IL-23 | Modest viral susceptibility, reduced IL-12 response and resistance to arthritis |