Biological effects of double-walled carbon nanotubes on the innate immune system: An in vitro study on THP-1 human monocytes

DWCNTs have numerous industrial and biomedical applications and several studies reported that they could act as immunomodulator systems. The immune system is the first line of defence of the human body when exposed to particulate matter. In order to investigate DWCNTs’ role on innate immunity, we used THP-1 monocytic cells for the purpose of this study.We showed that DWCNTs were not cytotoxic until 6 h, 24 h, 48 h and 72 h of incubation with THP-1 monocytic cells (concentrations tested from 10 to 50 μg/mL). From 6 h to 72 h of incubation of THP-1 cells with DWCNTs, we measured a significant increase of the baseline cell index using xCELLigence® technology showing cell adhesion. After 24 h of exposure, DWCNTs agglomerates were localized in THP-1 monocyte cytoplasm and cell adhesion was observed simultaneously with a significant increase in the expression of CD11b and CD14 cell surface proteins. Pro-inflammatory cytokine secretion (IL-1β, IL-6, IL-8, TNF-α and IL-10) was also measured in supernatants after 6 h or 24 h of exposure to DWCNTs. This pro-inflammatory response was increased in THP-1 monocytic cells pre-treated with LPS.Altogether, our data indicate that DWCNTs induce an increased pro-inflammatory response of THP-1 monocytes and seem to modulate cell surface protein expression confirming that DWCNTs could act as stimulators of innate immunity.