Production of IFN-γ by spleen lymphocytes in response to MADB106 tumor cells. Total spleen lymphocytes were incubated in the presence of MADB106 tumor cells. At selected time intervals (2, 6, 24 and 96 h), the levels of IFN-γ cytokine were determined in culture supernatants. In addition, B cells were removed from total splenic lymphocyte cultures. After 1 and 4 days of culture, supernatants were collected and the level of IFN-γ determined using ELISA techniques. Vertical bars and error bars represent the mean ± SE (n = 4). N.D. indicates IFN-γ production was not detectable. An asterisk (*) indicates a statistical difference (P less than or equal to 0.05) in the cytokine production by spleen cells. Asterisks (**) indicate a statistical difference (P less than or equal to 0.05) in the cytokine production between total and B cell-depleted groups.