THE ROLE OF NEWLY FORMED VESSELS AND CELL-ADHESION MOLECULES IN THE TISSUE-RESPONSE TO WEAR PRODUCTS FROM ORTHOPEDIC IMPLANTS

Neovascularization and activation of endothelial cells play an important role in recruitment of blood leucocytes at sites of inflammation. This study aimed to assess the pattern of vascular growth and the expression of cell adhesion molecules on vascular endothelium and inflammatory macrophages and T cells in the bone-implant interface from patients with aseptically loosened orthopaedic prostheses. ELAM-1, VCAM-1, ICAM-1 and the receptors LFA-1 and CR3 were immunolocalized on cryostat sections of the interface obtained during revision arthroplasty. The results showed that ELAM-1 was restricted to endothelium and was upregulated on different vessels in 21 cases. Its expression correlated strongly with the presence of metal wear debris. VCAM-1 was less frequently expressed (n=6 cases), and was co-expressed with ELAM-1 in three cases with metal debris. ICAM-1 was detected on a targe number of vessels on the bone side in 13 cases, but was more strongly expressed on macrophage subsets and foreign body giant cells (FBGCs) on the lining layer at the implant side. This study indicates the contribution of three different pathways in the migration of inflammatory cells to the bone-implant interface in response to phagocytosis of implant degradation products. Upregulated ELAM-1 expression may suggest a role in hypersensitivity reactions. Finally the persistent expression of VCAM-1 and ICAM-1 on macrophages and FBGCs in the lining layer indicates possible cellular interactions with the extracellular matrix proteins.