The role of retinoic acid-related orphan receptor variant 2 and IL-17 in the development and function of human CD4+ T cells.

Th17 cells are defined by their capacity to produce IL-17, and are important mediators of inflammation and autoimmunity. Human Th17 cells express high levels of the retinoic acid-related orphan receptor variant 2 (RORC2), but it is currently unclear whether expression of this transcription factor alone is sufficient to recapitulate all the known properties of Th17 cells. We used lentivirus-mediated transduction to investigate the role of RORC2 in defining aspects of the human Th17 cell lineage. Expression of RORC2 induced production of IL-17A, IL-22, IL-6 and TNF-alpha, a Th17-cell-associated chemokine receptor profile and upregulation of CD161. RORC2-transduced T cells were hypo-responsive to TCR-mediated stimulation, a property shared with ex vivo Th17 cells and overcome by addition of exogenous IL-2 or IL-15. Co-culture experiments revealed that RORC2-expressing cells were partially resistant to Treg cells since production of IL-17 and proliferation were not suppressed. Evidence that IL-17 stimulates CD4(+) T cells to produce IL-2 and proliferate suggested that the resistance of Th17 cells to Treg-mediated suppression may be partly attributed to IL-17 itself. These findings demonstrate that expression of RORC2 in T cells has functional consequences beyond altering cytokine production and provides insight into the factors regulating the development of human Th17 cells.