Monocyte-derived DCs are activated by pathogenic (invasive and noninvasive) or nonpathogenic bacteria. MoDCs were incubated with WT or attenuated strains of S typhimurium (described in “Materials and methods”), or with a laboratory strain of E coli (DH-5α) or with L plantarum (LP), at a ratio of 1 DC to 10 bacteria for 1 hour in medium without antibiotics. Cells were washed and incubated for an additional 23 hours in medium containing 100 μg/mL gentamicine to kill extracellular and intracellular bacteria. Cell culture supernatants were collected for cytokine measurements (IL-10 and IL-12p70) by ELISA. Cells were harvested and processed for FACS analysis after staining for CD83 surface expression. As shown, all of the tested bacteria induced production of IL-12 and IL-10 and induced substantial activation of MoDCs as attested by increase of surface expression of CD83. Data are shown as means (± SD, top) and are representative of 3 independent experiments. NT indicates not treated.