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Transient expression of T-bet epigenetically imprints the Ifng locus for its expression in a distinct Tfh cell subset

ABSTRACT: T follicular helper (Tfh) cells, which reside in the B cell follicles and help Ig class switching, express the master transcription factor BCL-6 and signature cytokine IL-21. Tfh cells are also capable of expressing IFN-g, however, whether IFN-g-producing Tfh population represents a unique Tfh subset and how they develop are unknown. While T-bet is the master regulator for IFN-g production in Th1 cells, Tfh cells express no or very low levels of T-bet. Here, by using a T-bet-fate-mapping mouse strain, we report that all the IFN-g-producing Tfh cells identified after immunization have previously expressed T-bet. DNase I hypersensitivity analysis indicates that the Ifng gene locus is partially accessible in this ‘ex-T-bet’ population but inaccessible in Tfh cells without a history of T-bet expression. Furthermore, multi-color tissue imaging shows that some “ex-T-bet” Tfh cells reside in germinal centers and express IFN-gin situ. Finally, IFN-g-expressing Tfh cells are absent in T-bet-deficient mice and the Ifng gene is inaccessible in T-bet-deficient Tfh cells. Thus, transient expression of T-bet epigenetically imprints the Ifng locus for cytokine production in Tfh cells. Our results also indicate that Tfh cells are composed of different subsets and they may use genetic programs similar to those of classical non-Tfh T helper cells in order to acquire unique cytokine producing capacity.RNA-Seq analysis of gene expression in splenic CD4+CD44highCD25- T cell subsets. RNA-Seq analysis of gene expression in antigen-specific Tfh cells and non-Tfh cells that have a history of T-bet expression. DNase 1-Seq of T-bet expressed and un-expressed Tfh cells and non-Tfh cells.

ORGANISM(S): Mus musculus

PROVIDER: GSE102959 | GEO | 2018/09/17

REPOSITORIES: GEO

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Project description:Follicular T helper cells (Tfh) are critical for providing help to B cells for germinal center (GC) formation. Mutations affecting SAP prevent GC formation due to defective T:B cell interactions, yet effects on Tfh cell differentiation remain unclear. We describe the in vitro differentiation of functionally competent “Tfh-like” cells that expressed IL-21, Tfh markers, and Bcl6, and rescued GC formation in SAP-deficient hosts substantially better than other T helper (Th) cells. SAP-deficient Tfh-like cells appeared virtually indistinguishable from wildtype, yet failed to support GCs in vivo. Interestingly, both Tfh-like and in vivo-derived Tfh cells could produce effector cytokines in response to polarizing conditions. Moreover, other Th cell populations could be reprogrammed to obtain Tfh characteristics. ChIP-Seq analyses revealed positive epigenetic markings on Tbx21, Gata3 and Rorc in Tfh-like and ex vivo Tfh cells, and Bcl6 in other Th cells, supporting the concept of plasticity between Tfh and other Th populations. We describe the in vitro differentiation of functionally competent IL-21-producing cells with Tfh-like properties. Importantly, transfer of low numbers of these cells induced GC formation in SAP-deficient hosts more effectively than other in vitro differentiated Th cells, suggesting they represent bona fide Tfh cell precursors. We have chosen the name “Tfh-like” cells for these in vitro differentiated IL-21 producing cells as they exhibit Tfh characteristics, but do not reside within B cell follicles. SAP-deficient Tfh-like cells were virtually indistinguishable from WT, yet nonetheless, failed to effectively contribute to Tfh cells and rescue GC formation in vivo. Evaluation of cytokine production as well as epigenetic chromatin modifications of genes encoding Th cell-specific transcription factors from either in vitro-generated Tfh-like cells or Tfh cells isolated directly ex vivo provided evidence for plasticity between Tfh-like and other Th cell populations. Our results provide insight into the requirements for differentiation and plasticity of Tfh cells, which are critical for the generation of effective long-term humoral immunity. RNA was prepared from subconfluent asynchronously proliferating cells using TRIZOL and purified by RNeasy MinElute Cleanup kit (Qiagen). Hybridization to Affymetrix GeneChip Mouse Genome 430 2.0 arrays was used to generate gene expression profiles of WT Tfh-like and SAP-deficient Tfh-like cells.