Table 2

 The four members of the Janus kinase (Jak) family and the major cytokines reported to activate them

JakCytokines that activatePhenotype of knockout*
*The phenotype associated with deficiency of each of the Jaks is also summarised.
SCID, severe combined immunodeficiency; IFN, interferon.
Jak1gp130 cytokines, type I IFNs, IFNγ, γc cytokinesPerinatally lethal, neurological defects, SCID
Jak2Erythropoietin, thrombopoietin, prolactin, growth hormone, βc cytokines,IFNγ, IL-12Embryonically lethal, defective erythropoiesis
Jak3γc cytokinesSCID
Tyk2gp130 cytokines, type I IFNs, IL-12, IL-23Modest viral susceptibility, reduced IL-12 response and resistance to arthritis