Response of monocytes exposed to phagocytosable particles and discs of comparable surface roughness

This in vitro study characterized the temporal cytokine expression profile from human monocytes exposed to phagocytosable Ti particles (0.78±0.12 μm) and to Ti discs of comparable surface roughness. Human THP-1 monocytes were cultured in six well tissue culture polystyrene (TCPS) plates. Each well was either bare, contained Ti particles (the particles were clearly engulfed by the monocytes), or contained a Ti disc. Half of the wells were treated with 1 μg/mL lipopolysaccharide (LPS), while the other half were left unstimulated. Unstimulated and LPS-stimulated cells in bare wells were the negative and positive controls, respectively. Supernatant was sampled from each well at 1, 6, 24, 48, and 72 h and assayed for the expression of nine different cytokines using a Luminex system. Three cytokines (IL-1β, GM-CSF and IL-13) gave little to no response under all conditions, while six cytokines (TNF-α, IL-6, MIP-1α, MCP-1, VEGF, and IL-1ra) were clearly detectable. Expression levels generally increased with culture time, particle concentration, and LPS stimulation. Most significantly, it was found that cells treated by Ti discs produced in many instances a higher cytokine expression than did particles.