Cobalt and Chromium Ions Impair Macrophage Response to Staphylococcus aureus Infection

Cobalt-chromium-molybdenum (CoCrMo) alloys are routinely used in arthroplasty. CoCrMo wear particles and ions derived from arthroplasty implants lead to macrophage-driven adverse local tissue reactions, which have been linked to an increased risk of periprosthetic joint infection after revision arthroplasty. While metal-induced cytotoxicity is well characterized in human macrophages, direct effects on their functionality have remained elusive. Synchrotron radiation X-ray microtomography and X-ray fluorescence mapping indicated that peri-implant tissues harvested during aseptic revision of different arthroplasty implants are exposed to Co and Cr in situ. Confocal laser scanning microscopy revealed that macrophage influx is predominant in patient tissue. While in vitro exposure to Cr³⁺ had only minor effects on monocytes/macrophage phenotype, pathologic concentrations of Co²⁺ significantly impaired both, monocyte/macrophage phenotype and functionality. High concentrations of Co²⁺ led to a shift in macrophage subsets and loss of surface markers, including CD14 and CD16. Both Co²⁺ and Cr³⁺ impaired macrophage responses to Staphylococcus aureus infection, and particularly, Co²⁺-exposed macrophages showed decreased phagocytic activity. These findings demonstrate the immunosuppressive effects of locally elevated metal ions on the innate immune response and support further investigations, including studies exploring whether Co²⁺ and Cr³⁺ or CoCrMo alloys per se expose the patients to a higher risk of infections post-revision arthroplasty.