DIFFERENCES IN IMMUNE RESPONSES BETWEEN SUBJECTS WITH PREVIOUS ASEPTIC LOOSENING VERSUS SURVIVING THA

Abstract

Introduction: Immune responses in patients susceptible to aseptic loosening may differ to those without this susceptibility. We compared stimulated cytokine mRNA and protein expression in peripheral blood mononuclear cells (PBMC) in 34 subjects (M:F 16:18; mean age 75 years) with previous revision surgery for aseptic loosening versus 28 subjects (14:14; 75 years) with well-fixed implants after Charnley THA for osteoarthritis.

Methods: Extracted PBMCs were stimulated with endotoxin (LPS 200ng/mL), endotoxin-free titanium particles (Ti, endotoxin level =0 Eu/mL), or particles with adherent LPS (TiLPS, 140 Eu/mL). Cell lysate IL-1α, IL-1β, IL-1RA, IL-6, IL-10, IL-18, and TNF mRNA were assayed after 3 hours stimulation using standard rqRT-PCR techniques. Cell supernatant IL-1β, IL-1RA, IL-6 and TNF protein were assayed after 24 hours stimulation using a multiplex method.

Results: mRNA and protein levels in non-stimulated cells were lower in revision versus control subjects for all cytokines (p< 0.05 all analyses). mRNA expression relative to baseline was greater in revision subjects versus controls for all cytokines and all modes of stimulation (LPS, Ti, and TiLPS, p< 0.05 all analyses). LPS induced the greatest inflammatory cytokine response at both the mRNA and protein level in both groups, TiLPS particles induced a more attenuated response, and responses to Ti particles were weakest. In the control group endotoxin free particles showed a negative cytokine mRNA response for IL-1α, IL-1β, and IL-6 (p< 0.05), and reduced protein levels for IL-1β, IL-1RA, IL-6, and TNF versus non-stimulated cells (p< 0.05).

Discussion: Patients with a susceptibility to aseptic loosening have lower baseline but greater stimulated immune responses versus patients without loosening that may contribute to the pathogenesis of aseptic loosening.