FIG. 4.

BLV infection alters the growth and proliferation of iPfB cells costimulated with CD154 and recombinant human IL-2 and -4. iPfB cells were cocultured with γ-irradiated J558L cells, expressing a membrane form of murine CD154, at a ratio of 1:10 (J558L cell to iPfB cell), and the medium was supplemented with 10 ng of recombinant human IL-2 and -4 (CD154 + IL-2+4) per ml. Cultures were established with 10 × 10⁶ iPfB cells exposed to culture supernatant from either OVK (CD154 + IL-2+4) or FLK (CD154 + IL-2+4/BLV) cells. A total of 4 × 10⁶ viable iPfB cells were transferred every 4 days to fresh medium supplemented with CD154 plus IL-2 and IL-4. (A) Viable-cell number was determined at each cell passage by counting total cell number with a Coulter particle counter and then determining the percent viable cells (propidium iodide exclusion) with a flow cytometer (FACScan). Incubation with BLV significantly (P < 0.001) increased viable-cell number throughout the 16-day culture period. (B) iPfB-cell proliferation was assayed at each passage by culturing 2 × 10⁵ viable cells in triplicate cultures for 4 h. During this time, cells were pulsed with 0.4 μCi of [³H]thymidine per well. Spontaneous proliferation was significantly (P < 0.05) increased following exposure to BLV. Data presented are the mean + 1 SD of values from three experiments. ∗, P < 0.05, +, P < 0.01.