Ectopic expression of macrophage scavenger receptor MARCO in synovial membrane-like interface tissue in aseptic loosening of total hip replacement implants.

Macrophage receptor with collagenous structure (MARCO) is a scavenger receptor with a very limited expression in healthy tissues. It was hypothesized that foreign body wear debris induces it to participate in handling of implant-derived particles in human synovial membrane-like tissue around aseptically loosening total hip replacement implants. A DNA microarray study showed that MARCO was upregulated in human monocytes by polymethyl methacrylate particles in cell culture. MARCO mRNA and protein were strongly expressed in numerous CD68 positive macrophages and foreign body giant cells in interface membrane lining and stroma around cemented implants, but was only present in a few cells in synovial membrane from osteoarthritis patients. A 65-kDa MARCO-reactive band was only found in interface tissue extracts. This is the first work to show upregulation of MARCO mRNA by foreign bodies in vitro. This is paralleled in vivo as MARCO mRNA and protein were over-expressed in chronic foreign body synovitis. As scavenger receptor MARCO apparently participates in handling of wear particles, which due to their nondegradable, irritating nature initiate/perpetuate foreign body inflammation, and peri-implant osteolysis.