Term placental explants were treated with 5×109- 5×1010/ml EVs derived from monocytes or macrophages, and culture supernatants collected at 24h. Explants were in 150μl culture media, equating to 1.5×108, 3.75×109 and 7.5×109 EVs per explant for the three doses. For the highest concentration of EVs (5×1010/ml), the mean number of initial cells plated was 2.2×106 monocytes and 4.7×106 macrophages per explant. A) Cytokine levels in culture supernatants assayed by ELISA showed that macrophage EVs induced significant dose-dependent increases in the production of IL-6, IL-8 and IL-1ß, with no such response seen to monocyte EVs (n=5 placentas). B) Luminex performed for the highest exosome dose (5×1010/ml) additionally showed that IL-10 and TNF-α and IL-1-α were significantly elevated in response to macrophage EVs, but not monocyte EVs (n=8 placentas). Asterisks above individual columns indicates a significant difference from the non-treated (NT). C) To confirm that cytokines detected were of placental origin, as previously shown for IL-6/IL-8[6], control wells of exosomes alone were incubated alongside placental explants at the highest concentration, and assayed for IL-1ß/TNF-α/IL-10/IL-1-α by ELISA (n=8 placentas). At least two different EV preparations were used for each cytokine measurement. *p<0.05, **p<0.01, ***p<0.001.