IL-12 is the major Th1-skewing factor in supernatants of SAC-activated DC. Naive Th cells were stimulated with CD3 MoAb and CD28 MoAb in the presence of rIL-2. rIL-12 (200 U/mL) or supernatants of 24-hour activated DC (DC-sup; final dilution 1:2) were added, the latter in the absence or presence of neutralizing anti-IL-12 (αIL-12). Th cells were cultured for 14 days and restimulated with CD3 and CD28 MoAb. Supernatants were procured after 24 hours and levels of IFN-γ and IL-4 were analyzed. Results are expressed as the percentage (mean ± SEM of three independent experiments) of the cytokine production of Th cells that were cultured in the absence of rIL-12, DC-sup, and αIL-12.