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 lipopolysacchride (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.

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