The Effect of TGF-β on the Induction CD8 and NK1.1 Expression in CTLL-2 Cell Line

Background: The presence of CD8⁺ T-cells expressing NK cell associated markers (TNK cells) has been observed in several experimental models, which suggests that NK cells may belong to the T-cell lineage. We used the CTLL-2 cell line, which is NK1.1⁺ CD3^-TCR⁺ CD4^- CD8^- cells in the presence of IL-2, to investigate whether these cells can be switched to CD8⁺ or CD4⁺ cells, like TNK cells, by the TGF-β. Methods: CTLL-2 cells were cultured with TGF-β or other cytokines and activators in the presence of IL-2. In order to see the surface and intracytoplasmic antigen expression in a single-cell level, simultaneous surface CD4, CD8, TCR with NK 1.1, and intracytoplasmic NK 1.1 staining was performed and three-color flow cytometric analysis was performed. Results: During routine passage, less than 5% of cells were CD8a although 20-40% of cells expressed CD8a when treated with IL-2 + TGF-β, whereas TPA + Calcium ionophore, IFN-γ, and TNF-α cause no significant changes in the proportion of CD8⁺ cells. Twenty percent of CTLL-2 cells expressed NK1.1 with IL-2 treatment, and this expression was also increased up to 65%-70% with IL-2 + TNF-β. Furthermore, most of the CD8 positive cells showed intracytoplasmic NK1.1. Conclusion: Our results indicated that these would be useful models to investigate CD8 precursor potentials in populations of CD4^-CD8^- (double negative) cells and the relationship of NK1.1. These results also support a role for TGF-β in T-cell differentiation and the hypothesis that T-cells and NK cells may have the same ontogeny.