Although regulatory T cells exert their effect on a multitude of different cell types, the pro-inflammatory CD4+ Th17 phenotype, which is characterized by expression of the retinoic acid-related orphan receptor (ROR-γt) and the production of the IL-17 cytokine family is of particular interest when trying to understand the implications of regulatory T cells in RA. Here, CD4 is linked to rheumatoid arthritis.