Comparison of the Response of Primary Human Blood Monocytes and the U937 Muman Monocytic Cell Line to Two Different Sizes of Alumina Ceramic Particles

It is well recognized that wear particles derived from orthopaedic implants have the potential to induce inflammation, which may eventually lead to aseptic loosening of the artificial joint. We hypothesized that alumina ceramic particles of different sizes cause a differential cytokine response by human monocytes. To test this hypothesis a human monocytic cell line (U937) and primary human blood monocytes obtained from healthy volunteers were exposed to ceramic particles within the range known to be generated in vivo. Cellular responses were measured by quantifying the relative gene expression of 12 different cytokines using TAQman Real-Time Polymerase Chain Reaction (RT-PCR). Our results demonstrate that at a particle to cell ratio of 100:1, 0.5 µm ceramic particles consistently provoked higher amounts of Interleukin-1α (IL-1α), IL-1ß, IL-8, IL-10 and Tumor necrosis factor-α (TNF-α) steady state mRNA by U937 cells. As expected, the variability of cytokine expression in primary blood monocytes was much higher compared to the cell line however, a similar trend was observed. These results show a differential response to ceramic particle size, which may imply that 0.5 µm particles are less biocompatible. New ceramic implants can be designed to generate a known particle size range in vivo. Implant materials of this type may induce relatively lower levels of production of inflammatory cytokines resulting in a reduced incidence of failure due to aseptic loosening