Interplay between CD45RA+ regulatory T cells and TNF-alpha in the regulation of human Th17 differentiation.

The balance between effector CD4(+) T cells secreting IL-17 (T(h)17) and regulatory T cells (Treg) plays an important role in autoimmune disorders that include rheumatoid arthritis (RA) and Crohn's disease. Tumor necrosis factor (TNF)-alpha is a key pro-inflammatory cytokine that contributes to disease pathogenesis. We investigated the interplay between CD45RA(+) Treg and TNF-alpha in the regulation of human T(h)17 differentiation. We found that CD45RA(+) Treg promoted while TNF-alpha inhibited naive CD4(+) T-cell differentiation into IL-17 and CCL20 co-expressing T(h)17 cells without influencing their IL-22 release. Unexpectedly, CD45RA(+) Treg depletion abrogated TNF-alpha suppressive function. Finally, dendritic cell-derived TNF-alpha suppressed the development of IL-17(+)CCL20(+) expressing T(h)17 cells. In conclusion, CD45RA(+) Treg positively governs human T(h)17 development, which is impaired by TNF-alpha. We propose that TNF-alpha may represent a negative feedback mechanism to control IL-17/CCL20- but not IL-22-associated autoimmune pathologies.