Interleukin-1 production by activated macrophages surrounding loosened orthopaedic implants: a potential role in osteolysis.

IL-1 producing cells at the bone-implant interface obtained during revision of loosened total joint replacements were demonstrated by immunohistochemistry on tissue sections. Other markers for the characterization of macrophages, B cells, T cell subpopulations, IL-2 receptor and HLA-DR antigens were also used. The 10 cases examined showed excessive metallosis within the cytoplasm of the macrophages and extracellular matrix. IL-1 beta containing cells were found in seven cases, four of which showed positive staining on more than 80% of the macrophages. A relatively similar proportion of T cells was seen in all the cases. T helper (CD4 positive) cells were always present in excess of T suppressor (CD8 positive) subtype. T cells showed no expression of detectable membrane IL-2 receptor. No B cells were found in these cases. Macrophages showed very strong immunostaining for HLA-DR. These findings indicate the possible induction of IL-1 production by activated macrophages in the interface in response to the presence of metallic wear debris. In view of the well known effect of IL-1 as a potent mediator of bone lysis, the results suggest a major role of the metal debris-containing macrophages in the process of osteolysis and subsequent implant loosening.