Stable Interactions and Sustained TCR Signaling Characterize Thymocyte–Thymocyte Interactions that Support Negative Selection

Abstract

Negative selection is one of the primary mechanisms that render T cells tolerant to self. Thymic dendritic cells play an important role in negative selection, in line with their ability to induce migratory arrest and sustained T cell receptor (TCR) signals. Thymocytes themselves display self-peptide/MHC class I complexes, and while there is evidence that they can support clonal deletion, it is not clear whether they do so directly, via stable cell-cell contacts and sustained TCR signals. Here we show that murine thymocytes can support surprisingly efficient negative selection of antigen-specific thymocytes. Further, we observe that agonist dependent thymocytethymocyte interactions occurred as stable, motile conjugates led by the peptide presenting thymocyte, and in which the trailing peptide-specific thymocyte exhibited persistent elevations in intracellular calcium concentration. These data confirm that self-antigen presentation by thymocytes is an additional mechanism to ensure T cell tolerance, and further strengthen the correlation between stable cellular contacts, sustained TCR signals, and efficient negative selection.

Sema3e/Plexin D1 Modulates Immunological Synapse and Migration of Thymocytes by Rap1 Inhibition

“…DP thymocytes exhibited relatively random and slow migration with repeated migratory arrest. This intermittent deceleration of migration speed was associated with transient elevation of intercellular calcium concentration ([Ca 2+ ] i ) upon TCR engagement with self-peptide/MHC in a positively selecting environment (4,45), reminiscent of TCR stopping of mature T cells upon Ag recognition (46). Simultaneous imaging of thymocyte trafficking and Rap1 activation showed that normal cortical thymocytes exhibited migration with modest Rap1 activity.…”

Methoxychlor metabolite HPTE alters viability and differentiation of embryonic thymocytes from C57BL/6 mice

“…It is not clear from the literature what role thymocytes play (as opposed to thymic stromal cells [TSC]: Brown, 2005; Melichar et al 2015) and which population(s) participate in responses to EDC. Data from chimeras (Staples et al 1999) suggest that ERα on stromal cells may be responsible for the decrease in thymic cellularity rather than ERα on thymocytes themselves.…”

“…The results thus cannot exclude a likelihood that TSC have a role in EDC-mediated toxicities in vivo (Kaplan et al 2015). Rather, it shows that in addition to potential TSC effects, EDC (like DES and HPTE) have direct effects on embryonic thymocytes similar to sustained thymocyte-thymocyte interactions that support negative selection (Melichar et al 2015). …”

A role for phagocytosis in inducing cell death during thymocyte negative selection

“…1a). We used flow cytometry to determine the ratio of viable OT-93 I:reference thymocytes remaining in the slice as a measure of negative selection 94 10,20,21 (Fig. 1a).…”

“…Although some non-phagocytic subsets, including mTECs, thymocytes, and B cells, 248 can induce negative selection 3,21,46 , this process may be rendered less efficient by 249 the requirement for a second cellular encounter with a phagocyte in order to 250 complete negative selection ( Supplementary Fig. 5b).…”