Phenotypic characteristics of T lymphocytes in the interfacial tissue of aseptically loosened prosthetic joints.

Aseptic loosening of prosthetic joints represents a major cause for revision surgery. Wear particles represent the initial stimulus in the production of a multi-cellular inflammatory membrane at the bone-implant interface. The mechanisms by which this membrane is established and its influence on bone resorption are central to understanding aseptic loosening. T cells have been identified as a component of interface tissue a feature confirmed in this study. Of the 15 cases studied, 12 cases (12/15) stained positive for CD3. T cell infiltration was present throughout the sections with some perivascular clustering. Multiplex PCR (MPCR) testing of eight of the 15 cases for Th1/Th2 cytokines did not show a predominance of either "type" of T cell response. Interleukin (IL)-2 mRNA expression was the most common feature (7/8) while IL-4 (6/8), IL-13 (6/8) and IFN-gamma mRNA expression (6/8) was also prevalent. IL-5 (4/8) and IL-10 (4/8) mRNA expression was less and IL-12 (3/8) mRNA expression was the least. Recent work has shown furthermore, that activated T cells can directly stimulate osteoclastogenesis through the expression of RANK ligand. However, although staining for RANK ligand was a consistent feature of all cases stained, such RANK ligand expression was limited to endothelial cells. Helper T cells control and develop immune responses, their role in the inflammation seen in aseptic loosening will aid further understanding of this reaction and may also identify key points for therapeutic intervention.