Cross-priming DC are the most effective stimulus in promoting the expansion of <i>S.</i> Typhi-specific T cells.

<p>Net frequencies of IFN-γ-spot forming cells (SFC) were assessed by an IFN-γ ELISPOT assay using <i>in vitro</i> expanded PBMC as effectors and autologous blasts infected with live <i>S.</i> Typhi as stimulators. PBMC were co-cultured with their own DC alone or DC that had been pulsed with live or heat-killed <i>S.</i> Typhi, or uninfected or <i>S.</i> Typhi-infected autologous blasts at a 1∶4 blast∶DC ratio. Net frequencies of IFN-γ SFC were calculated as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005879#s4" target="_blank">Materials and Methods</a>. The dashed line represents the cut-off for positive-ELISPOT assays determined as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005879#s4" target="_blank">Materials and Methods</a>. Bar graphs show means+SE of 3 experiments using 4 different donors (*, p<0.05 compared with DC pulsed with <i>S.</i> Typhi-infected cells).