The effect of TGF-beta on the induction CD8 and NK1.1 expression in CTLL-2 cell line

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-beta.

CTLL-2 cells were cultured with TGF-beta 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 NK1.1, and intracytoplasmic NK1.1 staining was performed and three-color flow cytometric analysis was performed.

During routine passage, less than 5% of cells were CD8a+, although 20-40% of cells expressed CD8a when treated with IL-2 + TGF-beta, whereas TPA + Calcium ionophore, IFN-gamma, and TNF-alpha 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-beta. Furthermore, most of the CD8 positive cells showed intracytoplasmic NK1.1.

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-beta in T-cell differentiation and the hypothesis that T-cells and NK cells may have the same ontogeny.