Cytokine production induced by particles in mono- and co-cultures. A): IL-6 release; B): IL-8 release; C): MCP-1 release; D): IL-1β release; E): TNF-α release. Untreated HUVECs or THP-1 cells served as negative controls. Data represent the mean ± SD, n = 3. ## p < 0.01, **p < 0.01, a significant difference between compared groups. (c: control, FeNPs: Fe3O4 particles; SiNPs: SiO2 particles, EC: endothelial cells).