IL-6 production by MSCs under different culture conditions. IL-6 production was evaluated in MSCs cultured alone or in combination with monocytes (either in the absence or in the presence of the PGE₂ inhibitor NS-398) with GM-CSF and IL-4. After 5 days, culture SNs were collected and IL-6 was measured by ELISA assay. Data are represented as mean ± SD of IL-6 levels (expressed as ng/mL) evaluated in 6 independent experiments performed. **P < .01.