Integration of epigenetic and transcriptional mechanisms governs functional commitment versus plasticity of gd T cell subsets

gd T cells are major innate sources of interleukin-17 (IL-17) and interferon-g (IFN-g), which are differentially produced by two thymically-derived subsets segregated on CD27 expression. However, the molecular mechanisms that program the functional differentiation of gd cells remain incompletely understood. Here we show that CD27+ gd cells are epigenetically committed to express Ifng but not Il17, whereas CD27- gd cells spontaneously make IL-17 but can be induced to produce IFN-g under specific inflammatory conditions. This “plastic” behavior of CD27- gd cells associates with permissive histone H3 marks at loci encoding Ifng and upstream “type 1” transcription factors. By contrast, Il17 and related “type 17” factors are epigenetically and transcriptionally active in CD27- but silenced in CD27+ gd cells. Hence, stable versus plastic behaviors of gd cell subsets are controlled by integrated epigenetic and transcriptional mechanisms that regulate the expression of “master” transcription factors and effector cytokine genes. ChIP was carried out on FACS-sorted cells from pooled spleen/ lymph nodes. The following antibodies were used: anti-histone H3K4me2 (07-030, Millipore) and anti-histone H3k27me3 (07-449, Millipore). Between 105 - 106 cells were crosslinked with formaldehyde and nuclei were isolated and sonicated with a Sanyo Soniprep 150 at an amplitude of 10 microns with 17 times 10s bursts, resulting in 200–400bp chromatin fragments. IP was carried out as previously described 49. The Immunoprecipitated DNA released from crosslinked proteins was extracted with the QiaQuick kit (Qiagen) in accordance with the manufacturer´s instructions. Deep sequencing was performed at the GeneCore facility of EMBL (http://www.genecore.embl.de/). At least 1 ng of immunoprecipitated DNA was used for library preparation according to the Illumina protocol.