Characterization of a regulatory T cells molecular meta-signature identifies the pro-enkephalin gene as a novel marker in mice

Regulatory T cells (Treg) are crucial in the proper balance of the immune system. A better characterization of Treg-specific genes should extend our knowledge on their complex biology. However, to date there is no consensual Treg signature in the literature. Here, we extracted a molecular Treg meta-signature relative to CD4+ conventional T cell from 8 different but comparable publicly available microarray datasets. We confirmed the validity of our result using the much larger but less stringent Immuno-Navigator database. However, many genes of the Treg meta-signature were also expressed at the protein level by other immune cell subsets, as assessed by mass cytometry, with the noticeable exceptions of Il2ra, Ctla4, and Tnfrsf9. Surprisingly, the proenkephalin (Penk) gene was a prominent member of this restricted Treg meta-signature. Further analysis of public datasets and of our own RNA sequencing experiments confirms that Penk was over expressed by Treg in various murine tissues, including thymic Treg. Interestingly, Penk expression was increased in intra tumoral Treg whereas it was down modulated in the central nervous system of mice suffering from EAE. Finally, we propose a mechanistic model linking TNFR signaling and the transcription factor Batf in the regulation of Penk expression in Treg. Altogether, our results provide the first Treg meta-signature in mice and identifies Penk as a novel and unexpected Treg marker.