ObjectivesThe aim of this study was to investigate the response of THP-1 monocyte-derived macrophages following exposure to titanium dioxide nanoparticles (TiO2 NPs) and microparticles (TiO2 MPs) in an in vitro system. DesignTHP-1 monocytes were maintained in RPMI medium and transformed into M0 macrophages using Phorbol 12-myristate 13-acetate (PMA). TiO2 particle size characterization was performed using scanning electron microscopy (SEM) and dynamic light scattering (DLS) technology. A viability study using an XTT assay was performed by treating THP-1-derived macrophages with TiO2 NPs (<100 nm) and TiO2 MPs (<5 μm) at concentrations ranging from 100, 50, 25, 12.5, 6.25 and 3.125 μg/mL. Macrophages were then treated with three different concentrations of NPs and MPs (5, 20 or 100 μg/mL) for 24 h, and ROS production and TiO2 particle cellular uptake were measured using ROS assays and flow cytometry, respectively. ResultsThere was no significant change in the viability of THP-1 monocytes after treatment with TiO2 NPs and MPs. The uptake of both particles was confirmed and showed an increase in ROS generation, and the MPs produced more ROS than NPs. The increase in ROS generation with NPs was concentration-dependent. ConclusionUptake of TiO2 NPs and MPs in macrophages at subcytotoxic levels generate ROS in a size- and dose-dependent manner.