Direct activation of mast cells by prosthetic biomaterial particles.

IL-4 is a mast cell and T cell produced immune cytokine that is important in the regulation of macrophage function. IL-4 has also been implicated in the induction of foreign body giant cell formation. In patients with long-term joint prostheses, a localized granulomatous inflammation develops in periarticular tissues and other organs where phagocytosis of particulate material from various prosthetic components takes place. In this study we used the inflammatory lesions of the bone-implant interface as a model to investigate the possible production, the frequency and the cellular source of IL-4. 40 samples of the interface membrane obtained from 25 patients undergoing revision of clinically failed implants were analyzed by immunohistochemistry. Cryostat sections were labeled with specific monoclonal antibodies to mast cell products: IL-4, tryptase and the receptor c-kit (CD117). The study has identified a significant level of production of IL-4 by mast cells in all the cases analyzed. There was an apparent difference in the number of mast cells in relation to the histological variants of the interface. The increase in the number of mast cells and IL-4 production was more pronounced in cases with heavy macrophage infiltrate than those exhibiting a predominance of giant cells. The findings imply that the recruitment of mast cell and IL-4 expression precede the granulomatous reaction and may have a role in the induction of a number of immunopathological changes related to mast cell activation by biomaterial particles.