Comparison of the response of primary murine peritoneal macrophages and the U937 human histiocytic cell line to challenge with in vitro generated clinically relevant UHMWPE particles
Affiliations: Immunology Research Laboratory, Division of Microbiology, The University of Leeds, Leeds, UK | Department of Orthopaedic Surgery, The General Infirmary at Leeds, Leeds, UK | Centre for Hip Surgery, Wrightington Hospital, Wigan, UK | Department of Mechanical Engineering, The University of Leeds, Leeds, UK
Note: [] Corresponding author: J. Bridget Matthews, Immunology Research Laboratory, Division of Microbiology, The University of Leeds, Leeds LS2 9JT, UK. Fax: +44113 2335638; E‐mail: micjbm@bmb.leeds.ac.uk.
Abstract: The response of primary murine macrophages and the U937 human histiocytic cell line to challenge with clinically relevant UHMWPE wear debris of known particle size and dose was evaluated. Particles with mean sizes of 0.24, 0.45, 1.71, 7.62 and 88 μm were co‐cultured with cells for 24 hours prior to assessment of cell viability and production of the osteolytic mediators IL‐1β, IL‐6, TNFα and, in supernatants from murine phagocytes, PGE2 and GM‐CSF. All particle fractions were evaluated at particle volume (μm3) to cell number ratios of 10 : 1 and 100 : 1 (and, additionally, 0.1 : 1 and 1 : 1 for U937 cells). These ratios had previously been identified as the most stimulatory and clinically relevant. Although the results for the cell line were highly variable, stimulation with phagocytosable particles (range 0.1 to 15 μm) resulted in enhanced levels of cytokine secretion by both murine macrophages and U937 histiocytes. The most biologically active particles were sub‐micrometre in size. However, U937 cells responded to wear debris at much lower particle volume to cell number ratios (>0.1 μm3 per cell) than the murine cells (>10 μm3 per cell). No GM‐CSF was produced by particle or LPS stimulated murine macrophages. Similarly, U937 histiocytes failed to secrete any IL‐1β. Neither macrophage population responded to stimulation with the largest (88 μm) particles. These results confirm earlier findings and suggest that the size of UHMWPE wear particles is a critical factor in macrophage activation. Moreover, primary murine macrophages have been demonstrated to be a suitable model for studying cell‐particle interactions in vitro.
