FIG. 4.

NK cells produce enhanced amounts of IFN-γ and TNF-α upon coincubation with NDV-infected cells. HeLa or T98G cells were infected with NDV Ulster or MTH-68 and cultured with primary NK cells in the presence of IL-2. For comparison, uninfected HeLa and T98G cells were cocultured with NK cells, or NK cells and infected (Inf.) tumor cells were cultured alone. IFN-γ and TNF-α secreted into the supernatants were quantified using respective lymphokine immunoassays. Means of triplicate values ± SEM are shown. Lymphokine production elicited by NDV-infected cells was statistically compared with lymphokine secretion in the presence of uninfected cells by Student's t test (*, P < 0.05; **, P < 0.01; ***, P < 0.001).