Abstract
Unlike metal-on-Polyethylene, metal-on-metal (MoM) implants seem to affect the adaptive immune response as evident from the associated perivascular infiltrate containing lymphocytes and plasma cells. This is more pronounced in implant failure secondary to aseptic loosening, and may represent the failure mode. A reduction in CD8+ T lymphocyte counts has also been described with Hip Resurfacing. MoM articulations produce a much smaller order of size of wear particles (nanoparticles) than metal-on- Polyethylene, which may be responsible for the observed adaptive immune system effects. We therefore analyzed the effects of CoCr nanoparticles (CoCrNP) on Dendritic Cells, T cells & B cells.
We produced CoCrNP using repetitive short spark discharges between electrodes of prosthetic CoCr alloy. Electron micrography and Brunauer-Emmet-Teller method both confirmed nanoparticle size. The following experiments were then undertaken.
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Dendritic Cells were cultured from mouse bone marrow and incubated with CoCrNP of varying concentrations for 24hrs, or lipopolysaccharide as a positive control. Activation status was then characterized by CD40 expression on fluorescence activated cell sorting (FACS) analysis.
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T Cell Viability; Cells from mouse lymph nodes were incubated with CoCrNP in varying concentrations. At 48hrs, Propidium Iodide (PI) was added and proportion of CD4+ lymphocytes that were PI+ve determined by FACS analysis.
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T Cell proliferation; Cells from mouse lymph nodes were cultured in medium without phenol red and incubated with μCD3 (anti CD3), μCD3 + CoCrNP, μCD3 + μCD28 or μCD3 + μCD28 + CoCrNP. At 48hrs, Almar Blue was added & difference in light absorbance at 570nm & 600nm was then used to determine T cell proliferation at 72hrs.
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Cells from lymph nodes of an MD4 (Hen Egg Lysozyme (HEL) specific B cell receptor transgenic) mouse were incubated with CoCrNP, HEL (positive control) or CoCrNP + HEL. B cell activation at 48hrs was characterised by CD40 and CD86 expression on FACS analysis.
We found CoCrNP did not significantly increase CD40 expression on DCs, neither did it alter CD40 or CD86 expression on B cells. Using a sublethal concentration of CoCrNP as determined from the viability tests, CoCrNP inhibited CD3 & CD3/CD28 dependent T-cell proliferation. This would indicate CoCrNP reduces T cell proliferation and/or survival, which may explain the observed reduction in CD8+ count with hip resurfacing. Understanding the development of the Peri-vascular infiltrate associated with MoM implants will however, probably require more complex (most likely in vivo) models.
Correspondence should be addressed to Mr Carlos A. Wigderowitz, Senior Lecturer, University Dept of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY
