JAK3 can be used for the signalling of IL-2, IL-4, IL-15 and IL-21 (as well as other cytokines); therefore patients with mutations in the JAK3 gene often experience issues affecting many aspects of the immune system.[52][53] For example, non-functional JAK3 causes SCID, which results in patients having no NK cells, B cells or T cells, and this would make SCID individuals susceptible to infection.[53] Mutations of the STAT5 protein, which can signal with JAK3, has been shown to result in autoimmune disorders.[54]