Semi-quantitative analysis of cytokines in MM THR tissues and their relationship to metal particles

Cytokines associated with osteolysis have been demonstrated in tissues surrounding failed metal-metal (MM) total hip replacements (THRs). The objective of the present study was to semi-quantify the amounts of inflammatory cytokines in tissues from 28 failed MM THRs, and determine their relationship with the quantity of metal particles. Paraffin sections were immunohistochemically stained with monoclonal antibodies: anti-IL-1-beta, anti-IL-6 and anti-TNF-alpha. Cytokines and metal particles were rated in 10 fields per tissue using standard light microscopy. Because of the use of light microscopy, only relatively large particles or agglomerations of particles were visible. Therefore, a polarized light and a semi-quantitative scheme based on the discoloration of cell cytoplasms induced by the presence of particles were used to evaluate the quantity of metal particles. Results showed an overall higher amount of IL-6 than IL-1beta while TNF-alpha remained at very low levels. For each patient, the average IL-1beta and IL-6 ratings decreased when the average particle rating increased, following a linear regression, with relatively high correlation factors (r=-0.69 for IL-1beta and r=-0.57 for IL-6). IL-1beta decreased about twice as fast as IL-6. TNF-alpha, remaining at very low levels, did not demonstrate any correlation with particle rating. When multiple tissues were available for the same patient, the correlation factors between the average cytokine and particle ratings were highly variable between samples, demonstrating the heterogeneity between the tissues from the same patient. At the cellular level, there was an even higher correlation between the quantity of metal particles and the production of IL-1beta and IL-6 (r=-0.99), while TNF-alpha did not demonstrate any correlation, remaining at very low levels. In conclusion, this study showed that tissues surrounding failed MM THRs with low to moderate quantities of metal particles can induce the production of potentially osteolytic cytokines. However, the overall number of cells producing these cytokines tended to be lower than that typically seen in tissues surrounding metal-polyethylene THRs.