Bioactive IL-12 p70 production by DCs, in contrast to IL-12 p40, is specifically induced by Ag-specific interactions with T cells.

DCs either unpulsed or pulsed with TT were used to activate an autologous TT-specific CD4⁺ T-cell line. Secretion of IL-12 p40 (top) and IL-12 p70 (bottom) was measured in supernatants of DC culture or supernatants of DC/T-cell cocultures at day 1, 2, and 3. For the coculture experiment, results for 2.5 × 10⁴ and 5 × 10⁴ DCs per well, at T/DC ratios of 40:1 or 20:1, respectively, are shown. The TT-specific CD4⁺ T-cell line did not produce IL-12 when stimulated by PMA + ionomycin or with anti-CD3/anti-CD28 coated beads (not shown). These results are representative of 2 different experiments.