A Zap70 gain-of-function mutation alters mouse thymic maturation.

The tyrosine kinase ZAP-70 is essential for T-cell activation and development, but the mechanisms regulating its activity remain unclear. Previous studies showed that the Src-family kinase LCK binds phosphorylated tyrosine 319 of ZAP-70 via its SH2 domain. Additionally, a gain-of-function ZAP-70 mutation involving the YEEI motif enhances LCK recruitment and TCR-mediated signaling. To investigate the physiological consequences of enhanced ZAP-70-LCK interaction in vivo, we generated a knock-in mouse model expressing the Zap70 YEEI gain-of-function mutation. Analysis of thymocyte development revealed that the Zap70 YEEI mutation altered T-cell maturation, resulting in increased differentiation of thymic regulatory T (Treg) cells and reduced thymic negative selection. In the peripheral T-cell compartment, mutant mice exhibited decreased surface expression of the TCRαβ complex and an increased frequency of memory CD4 T cells. These findings indicate that enhancing the ZAP-70-LCK interaction modifies signaling thresholds during thymic selection and peripheral T-cell homeostasis. Collectively, our results demonstrate that a gain-of-function mutation in Zap70 significantly reshapes T-cell development and maturation, highlighting the importance of regulated ZAP-70-LCK interactions in establishing immune tolerance and maintaining T-cell compartment balance.