IL-23 Promotes the Production of IL-17 by Antigen-Specific CD8 T Cells in the Absence of IL-12 and Type-I Interferons

Abstract In contrast to CD4 T cells, CD8 T cells inherently differentiate into IFN-γ-producing effectors. Accordingly, while generation of IFN-γ-producing Th1 CD4 T cells was profoundly impaired in mice deficient for both type-I IFN and IL-12 signaling in response to infection with Listeria monocytogenes, generation of Ag-specific, IFN-γ-producing CD8 T cells was unimpaired. However, a fraction of these CD8 T cells also produced IL-17 in an IL-23-dependent manner. Furthermore, the addition of IL-23 in vitro was sufficient for some naive CD8 T cells to differentiate into IFN-γ/IL-17 dual-producing cells and was associated with increased expression of ROR-γt and ROR-α. Addition of IL-6 and TGF-β to IL-23 further augmented ROR-γt and ROR-α expression and suppressed Eomes expression, thereby enhancing IL-17 production by CD8 T cells. A loss of cytotoxic function accompanied the production of IL-17, as the addition of IL-6 and TGF-β resulted in a marked reduction of granzyme B and perforin expression. Thus, CD8 T cells retain sufficient plasticity to respond to environmental cues and can acquire additional effector functions in response to their environmental context.