Maturing Human CD127+ CCR7+ PDL1+ Dendritic Cells Express AIRE in the Absence of Tissue Restricted Antigens.

Joannah R Fergusson,Michael D Morgan,Daisy Picavet,Melanie Bruchard,Frits Koning,Jan Piet Van Hamburg,Balthasar A Heesters,Hergen Spits,Mark S Anderson,John C Marioni,Vincent Van Unen,Nicole N Van Der Wel,Leonie Huitema,Sander W Tas,Georg A Holländer

doi:10.3389/fimmu.2018.02902

Abstract

Expression of the Autoimmune regulator (AIRE) outside of the thymus has long been suggested in both humans and mice, but the cellular source in humans has remained undefined. Here we identify AIRE expression in human tonsils and extensively analyzed these “extra-thymic AIRE expressing cells” (eTACs) using combinations of flow cytometry, CyTOF and single cell RNA-sequencing. We identified AIRE+ cells as dendritic cells (DCs) with a mature and migratory phenotype including high levels of antigen presenting molecules and costimulatory molecules, and specific expression of CD127, CCR7, and PDL1. These cells also possessed the ability to stimulate and re-stimulate T cells and displayed reduced responses to toll-like receptor (TLR) agonists compared to conventional DCs. While expression of AIRE was enriched within CCR7+CD127+ DCs, single-cell RNA sequencing revealed expression of AIRE to be transient, rather than stable, and associated with the differentiation to a mature phenotype. The role of AIRE in central tolerance induction within the thymus is well-established, however our study shows that AIRE expression within the periphery is not associated with an enriched expression of tissue-restricted antigens (TRAs). This unexpected finding, suggestive of wider functions of AIRE, may provide an explanation for the non-autoimmune symptoms of APECED patients who lack functional AIRE.

Highlights

Autoimmune regulator (AIRE) has primarily received attention due to its expression within the thymus and role in tolerance induction
These extra-thymic AIRE positive cells of the tonsil were localized within the T cell zone, at the boundary between the T cell paracortex and B cell follicles. eTACs have previously been described in mice as a bone marrow-derived CD45+ and Major Histocompatibility Class II (MHCII)+ APC population which expresses the epithelial marker EpCAM [12]
With t-distributed stochastic neighbor embedding (t-SNE) of all tonsil CD45+MHCII+ cells, and by using color as a third dimension to visualize the intensity of expression of specific markers, distinct clusters relating to conventional dendritic cells (CD11c; cDC) and plasmacytoid dendritic cells (CD123; pDC) were clearly visible (Figures 1B,C)

Summary

Introduction

Autoimmune regulator (AIRE) has primarily received attention due to its expression within the thymus and role in tolerance induction. Using AIREdeficient mice this study demonstrated the role of AIRE in promoting tissue-specific gene expression within the thymus and a related reduction in the self-reactivity of peripheral T cells. Expression of AIRE and associated tissue restricted antigens (TRAs) are largely restricted to a specific population of epithelial cells within the medulla (mTEC) [1], where developing thymocytes are screened for self-reactivity and deleted before release into the periphery. Together, these findings established thymic AIRE as the master transcription factor for central tolerance induction during T cell development

Methods

Results

Conclusion