CD226 knockout reduces the development of CD8+ T by impairing the TCR sensitivity of double-positive thymocytes

The costimulation molecule CD226 is widely involved in T cell differentiation, activation, and immune functional regulation in peripheral immune tissues. CD226-deficient mice have impaired immune response capacity. The function of CD226 in regulating T cell development in the thymus, a central immune organ, is not yet fully understood. We investigated the development of thymocytes using CD226 knockout mice and single-cell Sequencing techniques. CD226 begins to be expressed in the second half of thymocyte development, with a gradual increase from the double-positive (DP) to single-positive (SP) phase and higher levels of CD226 on CD8+ T cells than on CD4+ T cells from the SP phase to mature T cells. In the thymus of CD226KO mice, the proportion of DPT at the quiescent phase (DPT-Q), particularly the Gzma+ cluster that tends to be CD8+ T cells and CD5+ cluster that are undergoing positive selection, decreases dramatically. Afterward, the proportion of mature CD8+ T cells reduces dramatically. Depletion of CD226 impaired TCR activation signaling and diminished Akt/ERK/NF-κB/p38 phosphorylation levels. The diminished TCR responsiveness of DPT cells impedes their positive selection process and influences the maturation of CD8+ T cells. In mechanism, CD226 knockout enhanced DPT cell Apoptosis via impairing Akt phosphorylation. These results suggest that CD226 plays a significant role in T cell thymic development via modulation of TCR signaling, affecting CD8+ T cell maturation. This article is protected by copyright. All rights reserved.