Stimulation of human DC cytokine production by Ab-opsonized C. burnetii. Human monocyte-derived DC were infected for 24 h with C. burnetii (Cb), C. burnetii that had been incubated with naïve human serum (Cb + naïve), or C. burnetii that had been incubated with immune human serum (Cb + immune). Treatment of DC with E. coli LPS served as a positive control for stimulation. The production of IL-1β, IL-6, IL12p70 and tumor necrosis factor (TNF) by human DC was determined by BioPlex multiplex cytokine assay. Levels below the limits of detection of the assay are indicated with an asterisk. The results shown are from one experiment and representative of three independent experiments.