IL-12 polarization upon bacterial infection. DCs were infected with E. coli expressing OVA for 2, 4, or 6 h (DC/bacteria ratio of 1:20). (A) Intracellular accumulation (intra) and secretion (extra) of IL-12 were measured by ELISA at every time point after infection. (B) Kinetic of antigen presentation after infection. DCs were infected with E. coli -OVA and fixed after 2, 4, and 6 h. OT-I and OT-II cells were added to DCs, and the levels of IL-2 in the cell culture supernatant was tested by ELISA after 12 h of incubation. Results are presented as mean values of triplicate culture wells. One representative of three experiments with similar results is shown. (C) Staining profile of IL-12 (red) in the DC–T cell synapse formed using E. coli–infected DCs and OT-I cells (CFSE labeled).