YF17D elicits robust and diverse primary T helper cell responses in DC/T cell co-cultures. (a and b) Purified T helper cells were mixed with DCs that had been incubated with live or UV-inactivated YF17D. After 14 d, the cells were harvested and evaluated by flow cytometry for cytokine and CD154 expression after a short restimulation with autologous DCs targets that had been left untouched, pulsed with killed YF17D, or infected with live YF17D. All data plots show live CD4⁺-gated events. These are representative data of experiments done on cells from at least 10 volunteers. (c) Alternatively, the culture supernatants were harvested and evaluated by a multiplex cytokine analysis. Data representative of experiments done on cells from two volunteers.