IL-17 family member cytokines: regulation and function in innate immunity

Abstract

Recently, the IL-17 family member cytokines have become prominent subjects of investigation. IL-17 (IL-17A) is the best-described member of this family where its production has been mainly attributed to a specialized T helper subset of the adaptive immune response termed Th17. However, recent research on this and other Th17 cytokines has revealed new sources and functions of IL-17 family members in the innate immune response. This review will highlight recent advances in the field of IL-17 family member cytokines and will predominantly focus on the innate regulation and function of IL-17, IL-17F, and IL-25.

Figure 1

Differentiation pathways of CD4+ T helper cells compared to IL-17- and IFNγ-producing γδ T cells. γδ T cells utilize many of the same cytokines and transcription factors as Th cells for the regulation of cytokine production. The primary difference between the development of cytokine-committed αβ and γδ T cells seems to be that this process occurs in the thymus in the case of γδ T cells compared to the periphery in CD4+ t helper cells.

Figure 2

Many stimuli such as allergens or pathogens can induce several cell types to express IL-25. IL-25 functions on both innate effectors and adaptive T cells to promote type-2 immune responses. IL-25 plays pathogenic roles in allergic lung diseases and protective roles in helminth parasite infection and some organ-specific autoimmune diseases such as experimental encephalitis autoimmune disease (EAE) and colitis.