CD8 T cell sensory adaptation dependent on TCR avidity for self-antigens.

Adaptation of the T cell activation threshold may be one mechanism to control autoreactivity. To investigate its occurrence in vivo, we engineered a transgenic mouse model with increased TCR-dependent excitability by expressing a Zap70 gain-of-function mutant (ZAP-YEEI) in postselection CD8 thymocytes and T cells. Increased basal phosphorylation of the Zap70 substrate linker for activation of T cells was detected in ZAP-YEEI-bearing CD8 T cells. However, these cells were not activated, but had reduced levels of TCR and CD5. Moreover, they produced lower cytokine amounts and showed faster dephosphorylation of linker for activation of T cells and ERK upon activation. Normal TCR levels and cytokine production were restored by culturing cells in the absence of TCR/spMHC interaction, demonstrating dynamic tuning of peripheral T cell responses. The effect of avidity for self-ligand(s) on this sensory adaptation was studied by expressing ZAP-YEEI in P14 or HY TCR transgenic backgrounds. Unexpectedly, double-transgenic animals expressed ZAP-YEEI prematurely in double-positive thymocytes, but no overt alteration of selection processes was observed. Instead, modifications of TCR and CD5 expression due to ZAP-YEEI suggested that signal tuning occurred during thymic maturation. Importantly, although P14 x ZAP-YEEI peripheral CD8 T cells were reduced in number and showed lower Ag-induced cytokine production and limited lymphopenia-driven proliferation, the peripheral survival/expansion and Ag responsiveness of HY x ZAP-YEEI cells were enhanced. Our data provide support for central and peripheral sensory T cell adaptation induced as a function of TCR avidity for self-ligands and signaling level. This may contribute to buffer excessive autoreactivity while optimizing TCR repertoire usage.