FOXP3 and GARP (LRRC32): the master and its minion

The transcription factor FOXP3 is essential for the development and function of CD4(+)CD25(hi)FOXP3(+) regulatory T (T-reg) cells, but also expressed in activated human helper T cells without acquisition of a regulatory phenotype. This comment focuses on glycoprotein-A repetitions predominant (GARP or LRRC32) recently identified as specific marker of activated human T-reg cells, which may provide the missing link toward a better molecular definition of the regulatory phenotype.