Live-cell imaging reveals the relative contributions of antigen-presenting cell subsets to thymic central tolerance

Abstract

Both medullary thymic epithelial cells (mTEC) and dendritic cells (DC) present tissue-restricted antigens (TRA) to thymocytes to induce central tolerance, but the relative contributions of these antigen-presenting cell (APC) subsets remain unresolved. Here we developed a two-photon microscopy approach to observe thymocytes interacting with intact APCs presenting TRAs. We find that mTECs and DCs cooperate extensively to induce tolerance, with their relative contributions regulated by the cellular form of the TRA and the class of major histocompatibility complex (MHC) on which antigen is presented. Even when TRA expression is restricted to mTECs, DCs still present self-antigens at least as frequently as mTECs. Notably, the DC subset cDC2 efficiently acquires secreted mTEC-derived TRAs for cross-presentation on MHC-I. By directly imaging interactions between thymocytes and APCs, while monitoring intracellular signaling, this study reveals that distinct DC subsets and AIRE + mTECs contribute substantially to presentation of diverse self-antigens for establishing central tolerance.

Toll-like receptor signaling in thymic epithelium controls monocyte-derived dendritic cell recruitment and Treg generation

“…It has been previously documented that distinct subtypes of thymic DCs vary in their capacity to acquire antigens from TECs 6,10,11,16 . Whereas CAT of TdTOM from TECs to cDC1 and cDC2 is very potent in the Foxn1 Cre ROSA26 TdTOMATO system, it is limited in the case of pDC (Fig.…”

“…It has become clear that developing thymocytes encounter selfantigens presented by various types of thymic APC, including mTECs 47 , B-cells 58 , pDCs 14 , and cDCs 11,59 . Although the generation of thymic Tregs was shown to be dependent on antigen presentation by both mTECs and DCs 4,47 , thymic cDCs seem to be particularly important for this process 6,17,60 .…”

“…mTECs mediate the promiscuous expression of thousands of otherwise strict tissuerestricted self-antigens (TRAs), a large number of which are under the control of the transcriptional regulator Aire 2 . The presentation of TRAs by mTECs can result in either the deletion of self-reactive T cells 3 or their conversion into Tregs 4,5 It has been recently demonstrated that the process of cooperative antigen transfer (CAT) from mTECs to DCs is essential for the establishment of thymic tolerance [6][7][8][9][10][11] . The complexity of CAT is foremost due to the heterogeneity of DCs in the thymus.…”

Distinct Subcellular Compartments of Dendritic Cells Used for Cross-Presentation

“…cDC2 mainly trigger the T H 2 response and show restricted CP ability as compared with cDC1s [24,37,38,39]. However, they efficiently present secreted antigenic peptides loaded on MHC I, in the thymus, for central tolerance [40]. Similar to cDC1s, cDC2s produce several different cytokines and express cell-surface-associated molecules to prime naïve CD4 + T cells into Tregs, Th2, or Th17 cells [18].…”

Factors that influence the thymic selection of CD8αα intraepithelial lymphocytes

“…Our observation that both peptide presentation by hematopoietic cells, as well as exogenous IL-2 and IL-15, enhanced certain aspects of the CD8αα IEL developmental program, suggest that thymic microenvironments enriched in these factors would support CD8αα IEL development. Medullary thymic epithelial cells (mTECs) are the major source of IL-15 in the thymus and closely associate with hematopoetic cells such as thymic DC 29,48,49 . Thymic IL-2 derives from hematopoetic cells, particularly thymocytes 50 , and there is also evidence that spatial linkage of IL-2 with antigen presenting cells such as DC promotes tT reg development 10,26 .…”