Diversity of cell phenotypes among MT-2 cell lines affects the growth of U937 cells and cytokine production

We previously reported the diversity of structure and integration sites of human T-cell leukemia virus type 1 (HTLV-1) provirus among different MT-2 cell lines. This raised the question as to whether cell phenotypes also differed among MT-2 cell lines. The influence of two different MT-2 cell lines (MT-2J and MT-2B) on the growth of the promonocytic leukemia cell line, U937, was investigated. Protein levels and mRNA expression of cytokines were also investigated. In addition, Western blot analysis of HTLV-1 regulatory proteins, Tax and HBZ, was also performed. Culture supernatant from MT-2B, but not MT-2J, cells showed marked suppressive effects on U937 cell growth. MT-2B showed high tumor necrosis factor (TNF)-α, TNF-β, and interferon (IFN)-γ both in protein levels of the culture supernatant and mRNA levels of the cells. Analysis using recombinant cytokines indicated that the suppressive effects of MT-2B were due, at least in part, to high levels of TNF-β and its synergic effects with IFN-γ in the culture supernatant. Protein levels of HTLV-1 Tax and HBZ were higher in MT-2B than those in MT-2J cells. These molecules have been reported to affect the cytokine production of HTLV-1 infected cells; therefore, the difference in these molecules may have accounted for the differences in cytokine production between MT-2J and MT-2B cells. Furthermore, because MT-2 cells showed a large variation of integrated HTLV-1 proviruses as well as cell phenotypes, it is important to exercise caution in the assessment and interpretation of experimental data from MT-2 cells.