Lack of correlation between mycoplasma induced IFN-gamma production in vitro and natural killer cell activity against FLD-3 cells.

Interferon (IFN) stimulates natural killer (NK) cell-mediated lysis of tumor cells. However, it is not clear whether IFN production is essential for NK cells to lyse their target cells in vitro, especially in long-term (greater than 18 hrs) assays. To investigate this, 0.5 X 10(6) normal mouse spleen cells were cocultured in RPMI 1640 medium with Friend erythroleukemia cells (FLD-3) (1 X 10(4] for 24 hours under conditions which cause lysis of FLD-3 cells. Supernatant fluid from such cultures demonstrated antiviral activity (100-200 units) which could be identified as IFN-gamma. Prior filtration of spleen cells over nylon wool, and pretreatment with anti-Thy-1.2 + C' abrogated their ability to generate IFN-gamma without affecting their NK (FLD-3) activity. The IFN-gamma producing cell which could also be detected in spleens of nu/nu BALB/c mice lacked cell surface, Lyt-1, Lyt-2, and NK-1.2 antigens. The stimulus for IFN-gamma induction appeared to be Mycoplasma arginini carried in the FLD-3 tumor cells. Although mycoplasma-free FLD-3 cells failed to induce IFN in vitro, they retained their susceptibility to NK cell-mediated lysis. We conclude that IFN induction is not essential for NK(FLD-3) cell-mediated lysis; indeed IFN detected in NK cell assays may be produced in response to mycoplasma infection of the tumor cells. The Thy-1.2 positive cells stimulated by mycoplasma to produce IFN-gamma lack several characteristics of T-cells or NK cells.