IL-17+ CD8+ T cells: Differentiation, phenotype and role in inflammatory disease

•IL-17A (IL-17) is produced by multiple cell subsets, including CD8+ T cells.•The presence of IL-17+ CD8+ T cells in human inflammatory diseases suggests these cells may contribute to immunopathology.•Increased knowledge of human IL-17+ CD8+ T cells will enhance our overall understanding of their role in human disease.

The pro-inflammatory cytokine interleukin-17A (IL-17) has been the subject of research by many groups worldwide. IL-17 expression is often associated with a specific subset of CD4+ T cells (the so-called Th17 cells); however various other immune cell subsets can also synthesise and express IL-17, including CD8+ T cells. Here we review recent data regarding the presence of IL-17+ CD8+ T cells (also known as Tc17 cells) in human inflammatory disease, discuss current knowledge regarding the culture conditions required for the differentiation of these cells in humans and mice, and describe key phenotypic and functional features. Collectively, this information may shed light on the potential pathogenic role that IL-17+ CD8+ T cells may play in human inflammatory disease.