Murine CD8⁺ Invariant Natural Killer T Cells are Negatively Selected by CD1d Expressed on Thymic Epithelial Cells and Dendritic Cells

Background: CD1d-dependent invariant natural killer (iNKT) cells are found as either CD4 single positive (SP) or CD4/CD8 double negative (DN) cells in mice. The size of the CD8⁺ iNKT population is extremely small. It is known that CD1d expression on developing thymocytes is sufficient for iNKT development and co-receptor choice, which is driven by Th-POK expression. This study aimed to examine the factors involved in the CD4/CD8 co-receptor choice of iNKT cells in addition to Th-POK-driven silencing of CD8 expression. Methods: In this study, we compared iNKT cells of wild-type (WT) mice with those of transgenic mice in which CD1d expression is restricted to developing thymocytes by the proximal Lck (pLCK) promoter. CD8 positive iNKT cell population were analyzed by flow cytometry. Results: We found that there was a substantial population of CD8⁺ iNKT cells in the thymus and spleen of transgenic mice, and these cells are negatively selected in between Stage 2 and Stage 3 of their developmental program by the CD1d expressed on Thymic epithelial cell (TEC) and Dendritic cells in WT mice. Conclusion: We conclude that TEC expression of CD1d in the murine thymus contributed to co-receptor choice of iNKT cells, in addition to Th-POK-driven silencing of CD8. Therefore, mostly CD4 SP and DN iNKT cells are produced under normal physiological conditions in mice.