Pertussis toxin–treated DCs are impaired in the ability to activate CD4⁺ T cells. (A,B) CD4⁺T cells (4 ×10⁴) were incubated with DCs, pulsed with 100 ng/mL of TSST1, pretreated (+PTX) or not (−PTX) with PTX. CD69⁺ expression on CD4⁺ T cells was analyzed by FACS. (A) Histograms of CD69 expression on CD4⁺ T cells cocultured with DCs at a DC/T ratio of 1:4 in round or flat-bottom wells; percentages of CD69⁺/CD4⁺ T cells are indicated. (B) For each DC/T cell ratio, data were normalized to the percentage of CD69⁺/CD4⁺ T cells obtained in the cocultures of untreated DCs (= 100%). Means and SD of 3 experiments are shown. For the indicated ratio, overnight supernatants from PTX-pretreated DCs were added to the cocultures (▒) (C) Flow cytometric analysis of DC maturation markers in the flat-bottom cocultures. (D) CD4⁺ T cells were added to the upper chamber of a transwell system together with untreated or PTX-treated DCs (DC_PTX) and migration toward CXCL12 was analyzed. Significance was assessed by Student unpaired t test (*P < .05; **P < .005). Error bars represent SD.