Association between apoptotis and CD4(+)/CD8(+) T-lymphocyte ratio in aseptic loosening after total hip replacement

Particle-induced osteolysis is a major cause of aseptic loosening after total joint replacement. While the osteolytic cascade initiated by cytokine release from macrophages has been studied extensively, the involvement of T-lymphocytes in this context is controversial and has been addressed by only a few authors. In a former study we detected that the quantity of T-lymphocytes may be influenced by apoptosis in patients with aseptic loosening. In this study we intended to find out more details about the apoptosis-induced shifting of the T-cell number. We focused our interest on the CD4(+) and CD8(+) T-cells and their relative ratio. Caspase-3 cleaved was evaluated immunohistochemically to detect apoptotic T-cells in capsules and interface membranes from patients with aseptic hip implant loosening and a varying degree of caspase-3 cleaved expression in CD4(+) and CD8(+) T-lymphocytes was detected. Moreover, a relationship between the intensity of the apoptotic reactions and the radiological extent of osteolysis was observed. The number of CD4(+) cells was decreased in the presence of strong apoptotic reactions, respectively extensive osteolysis, while CD8(+) cells were affected to a much lower degree. Thus, the CD4(+)/CD8(+) ratio changed from 1.0 in cases with only small areas of periprosthetic osteolysis and minimally intense apoptosis to 0.33 in cases with large areas of osteolysis. This may suggest a causal relationship between the apoptosis-induced shift in the CD4(+)/CD8(+) ratio and the osteolysis respectively aseptic loosening. It is possible that these findings may lead to a new understanding of particle-induced osteolysis.