Identification of macrophage migration inhibitory factor in synovial membranes of loosened total joint replacement.

Endosteal bone resorption often occurs around loosened total joint replacements. In the process of the loosening, macrophages play an important role by releasing cytokines such as interleukin-1, tumor necrosis factor-alpha and prostaglandin E2. In this study, we investigated the involvement of macrophage migration inhibitory factor (MIF) in the pathological state of the loosening of a total hip replacement. Interface membranes were harvested from bone-cement or bone-implant interfaces of two patients during revision hip surgeries. The tissues were immunohistochemically examined with a polyclonal antibody against human recombinant MIF. This study detected MIF in the cytoplasm of the macrophages in all the tissues tested, though it was not detected in that of interstitial cells. The expression of MIF mRNA in the membrane was also examined by reverse transcription polymerase chain reaction, which demonstrated that expression of the MIF mRNA in the interface membranes was higher than that of the normal synovium. Considering these results, it is suggested that MIF is one of important cytokines mediating the inflammatory process during loosening of total joint replacements.