The unwavering commitment of regulatory T cells in the suppression of autoimmune encephalomyelitis: another aspect of immune privilege in the CNS.

FoxP3(+) regulatory T (Treg) cells accumulate in the central nervous system (CNS) during experimental autoimmune encephalomyelitis and have been shown to limit the extent of neuroinflammation and to facilitate clinical recovery. The recent demonstration that Treg cells lose FoxP3 expression and assume effector cell characteristics upon stimulation with proinflammatory cytokines has raised questions about their stability in the inflamed CNS. In this issue of the European Journal of Immunology, O'Connor et al. [Eur. J. Immunol. 2012. 42: 1164-1173] show that CNS-infiltrating Treg cells maintain their suppressor phenotype by downregulating the IL-6 receptor. This commentary discusses the finding particularly with relevance to therapy of multiple sclerosis.