Fig. 1.
Necrotic, but not intact, tumour cells K562 and JAr stimulate DCs to secrete IL-12p40. Monocyte-derived DCs (3 × 105/ml) were co-cultured with heat-killed (a and b), freeze/thaw-killed (c and d) or non-injured K562 or JAr cells (3 × 105/ml except in (a) when K562 cells were added to DCs at varying ratios as shown), and IL-12p40 concentration in the culture supernatants was measured (Materials and methods). Heat-killed K562 cells were added to monocytes at different stages of differentiation into DCs (e). Non-injured K562 cells do not stimulate secretion of IL-12p40 by dendritic cells over 48 h (f). Compared with non-injured cells, killed K562 cells stimulated significantly more IL-12p40 secretion, both when (a) heat (at a 1 : 1 ratio, P = 0·008) and (c) freezing/thawing (P = 0·043 in three donors) were used to induce necrosis. Similarly, compared with non-injured cells, killed JAr cells stimulated significantly more IL-12p40 secretion, both when (b) heat (P = 0·005) and (d) freezing/thawing (P = 0·011) were used to induce necrosis.