Individual susceptibility to periprosthetic osteolysis is associated with altered patterns of innate immune gene expression in response to pro‐inflammatory stimuli

Susceptibility to osteolysis after total hip arthroplasty (THA) varies between individuals. We examined whether patients susceptible to osteolysis (group I, n = 34 subjects) after cemented Charnley THA have quantitatively different innate immune responses to pro‐inflammatory stimuli versus patients without this susceptibility (group II, n = 28 subjects) at a mean of 14 years after primary surgery. Extracted peripheral blood mononuclear cells were stimulated for 3 h using endotoxin (lipopolysaccharide—LPS, 100 ng/mL), endotoxin‐stripped titanium particles (Ti) or endotoxin‐stripped particles with adherent LPS added‐back (TI + LPS). Subjects returned 1 week later and the experimental protocol was repeated. Assays for mRNA induction for interleukin (IL)‐1α, IL‐1β, IL‐1Ra, IL‐6, IL‐10, IL‐18, and tumor necrosis factor (TNF) were made using quantitative real‐time PCR. Although baseline levels of mRNA expression were slightly lower in group I, inducibility of mRNA expression was markedly greater in group I versus group II for all cytokines in response to LPS or Ti + LPS, and for IL‐1α in response to Ti (P < 0.05). LPS or Ti + LPS stimulation also resulted in an increase in the IL‐1/IL‐1Ra mRNA ratio in group I versus group II (P < 0.05). mRNA induction was highly reproducible between subject visits (r > 0.7, P < 0.001). Osteolysis‐susceptible patients show repeatable, quantitatively different patterns of innate cytokine gene expression in response to pro‐inflammatory stimuli versus THA patients who do not display this susceptibility. These innate immune differences may contribute to the variation in osteolysis‐susceptibility observed clinically between individuals.