Abstract
Introduction: UHMWPE wear debris is known to be a major cause of periprosthetic osteolysis and the long-term failure of total joint replacements by a macrophage-mediated mechanism. The aim of this study was to compare the in vitro response of mononuclear phagocytes from patients undergoing total hip arthroplasty to challenge with polyethylene particles or stimulation with lipopolysaccharide (LPS).
Methods: Peripheral blood was taken from 2 healthy donors and 16 patients admitted to hospital to undergo total hip arthroplasty. Human mononuclear phagocytes were isolated by density centrifugation. Polyethylene particles were sequentially filtered to obtain biologically active particles (0.1–0.6 μm diameter). Cells plus particles, cells plus LPS and cells only were co-cultured in supplemented RPMI-1640 culture medium. Culture supernatants were harvested and the concentration of TNFα quantified by ELISA. Mean specific activity was calculated.
Results:.
| TNFα | levels Particle stimulation | LPS stimulation |
|---|---|---|
| Control | 0.043–0.059 | 0.097–0.208 |
| Patients | 0–1.1 | 0.03–17.693 |
When considering all the subjects, no correlation was found between the response of their cells to polyethylene particles and LPS stimulation. However the cells of four subjects gave a much higher response to LPS than the rest and when these where excluded the correlation between the response to LPS and PE particles was significant with an R2 value of 0.9076.
Discussion: Despite the different mechanisms by which PE particles and LPS activate macrophages, the patient group with ‘normal’ or low response to LPS had a significant correlation in their response to LPS and particle stimulation. Why a small number of subjects had a much higher response to LPS without a proportional response to PE particles is not known, but it could be due to an increased expression of LPS receptors or genetic polymorphism. A greater than ten-fold difference in the patient response to particles may be of clinical importance in their potential susceptibility to loosening through osteolysis.
The abstracts were prepared by Peter Kay. Correspondence should be addressed to him at Centre for Hip Surgery, Wrightington Hospital, Appley Bridge, Wigan WN6 9EP.
