Figure 1

Role of cytokines in DC and T-cell interactions. Dendritic cells (DCs) produce IL-12 and IL-18; these favour the T-helper (Th)1 pathway, which is characterized by the transcription factor T-bet and the production of IFN-γ. The Th17 pathway results from the combined action of transforming growth factor (TGF)-β plus IL-6 and of IL-23. This pathway is characterized by the transcription factor retinoid-related orphan receptor (ROR)γt and by the production of IL-17. The effector Th1 and Th17 pathways are under the control of the regulatory pathway that is characterized by the transcription factor FoxP3 and the production of TGF-β and IL-10. Defects in this pathway may contribute to the consequences of the chronic RA synovitis that leads to destruction and lack of repair. It should be noted that some of these concepts have been established in the mouse; it is unclear to what extent they apply to humans.