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

• Published in: Immunology Vol. 169; no. 1; pp. 83 - 95
• Main Authors: Ma, Jingchang, Liu, Yitian, Duan, Chujun, Wu, Shuwen, Xie, Yang, Yang, Lu, Li, Xuemei, Wang, Yuling, Zhang, Yuan, Zhuang, Ran
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.05.2023
• Subjects: AKT protein; Animal tissues; Animals; Apoptosis; CD226; CD4 antigen; CD4 Antigens; CD5 antigen; CD8 antigen; CD8 Antigens; CD8+ T cell; CD8-Positive T-Lymphocytes; Cell activation; Cell Differentiation; Clonal selection; Clusters; Depletion; Differentiation (biology); Immune response; Immune system; Lymphocytes; Lymphocytes T; Maturation; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphorylation; Positive selection; Proto-Oncogene Proteins c-akt; Receptors, Antigen, T-Cell - genetics; Signaling; single‐cell sequencing; T cell receptors; Thymocytes; Thymus; Thymus Gland; single-cell sequencing; CD226; positive selection; thymocytes; CD8+ T cell
• ISSN: 0019-2805; 1365-2567
• DOI: 10.1111/imm.13612

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 began 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) increased, of which the Gzma+ cluster that tends to be CD8+ T cells and CD5+ cluster that is undergoing positive selection decreased dramatically. Afterward, the proportion of mature CD8+ T cells reduced dramatically. Depletion of CD226 impaired TCR activation signalling and diminished AKT/ERK/NF‐κB/p38 phosphorylation levels. The diminished TCR responsiveness of DPT cells impeded their positive selection process and influenced 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 signalling, affecting CD8+ T cell maturation. CD226 provides active signals to strengthen TCR downstream signalling. CD226 knockout impairs the positive selection of DPT cells, thus impedes the development of CD8+ T in the thymus.