白介素21在自體免疫和癌癥中扮演的角色。Role of IL-21 in autoimmunity and cancer. IL-21 is involved in reciprocal cross talk between disparate cell types, leading to effects on innate immune responses and adaptive antibody and cellular immune responses. This, in turn, may lead to autoimmune responses against normal or malignant tissues.

Interleukin-21 （IL-21） has synergistic effects on CD8+ T-cell proliferation in combination with either IL-7 or IL-15. The signal-transduction pathways that are downstream of each of the receptors are shown. Each of these common cytokine-receptor γ-chain （γc）-dependent cytokines signals through a Janus activated kinase 1 （JAK1） interaction with its corresponding cytokine-specific type-I-receptor protein and a JAK3 interaction with γc. IL-21-mediated signalling leads to the activation of mainly signal transducer and activator of transcription 1 （STAT1） and STAT3, whereas IL-7-mediated signalling and IL-15-mediated signalling mainly activate STAT and STAT5B. We have shown that signalling to CD8+ T cells that is mediated by either IL-21 or IL-15 activates unique gene-expression programmes that include the induction of the genes encoding granzyme A, B-cell lymphoma 3 （BCL-3） and JAK3 by IL-21 and those encoding BCL-2, MYC and cyclin D2 by IL-15 . In this study, a unique set of genes was shown to be induced by the combination of IL-21 and IL-15, including the genes encoding granzyme B, JUN and CXC-chemokine receptor 4 （CXCR4）. IL-2Rβ, IL-2 receptor β-chain; IL-7R, IL-7-receptor subunit; IL-15Rα, IL-15 receptor α-chain; IL-21R, IL-21-receptor subunit.