Figure 2

A subpopulation of IL-15-activated PBL induces TNF synthesis in monocytic cells. (a) Peripheral blood lymphocytes (PBL) were stimulated with IL-15 at 50 ng/ml for 24 hours and then co-cultured with THP-1 cells for 24 hours; the ratio of lymphocytes to monocytes was 10:1. Under some conditions, lymphocytes or THP-1 cells were fixed with 0.05% glutaraldehyde at 4°C for 30 to 45 s and washed intensively with sterile PBS before co-culture. The data shown are the TNF concentration in the supernatant and are expressed as means ± SEM (n = 5). (b, c) PBL were stimulated as in (a) and then incubated together with THP-1 cells for different durations (2 to 24 hours) (b) or at different cell ratios (1:1 to 50:1) (c). The data shown are the TNF concentration in the supernatants and are expressed as means ± SEM (n = 5).