Why Peri-Implant Tissues Are Susceptible to Inflammatory Breakdown-Single-Cell Transcriptomics Reveals Immune Priming in Clinically Healthy Peri-Implant Mucosa and CXCR2+ Neutrophil Activation in Peri-Implantitis.

AIM: Peri-implant tissues are more susceptible than gingiva to rapid inflammatory breakdown, but the cellular basis of this vulnerability remains unclear. This study investigated (1) whether clinically healthy peri-implant mucosa already displays an immune landscape distinct from healthy gingiva, and (2) which cellular states and molecular pathways characterize the transition from peri-implant health to peri-implantitis.

METHODS: An integrative single-cell RNA-sequencing analysis was performed using clinically healthy pre-loading peri-implant mucosa (n = 3), healthy gingiva (n = 17), and peri-implantitis tissues (n = 3). Healthy peri-implant mucosa was first compared with a healthy gingival reference atlas to define the baseline peri-implant immune niche. Disease-associated changes were then examined by comparing healthy peri-implant and peri-implantitis tissues. Key findings were validated in independent tissue cohorts comprising healthy gingiva, clinically healthy peri-implant mucosa, and peri-implantitis (n = 6 participants per group) using multiplex immunofluorescence, immunohistochemistry, and reactive oxygen species (ROS) detection.

RESULTS: Clinically healthy peri-implant mucosa showed greater immune-cell enrichment than healthy gingiva, most notably within the myeloid compartment. Among myeloid cells, a CXCR2+ neutrophil subset exhibited the highest baseline signature for neutrophil extracellular trap (NET) formation, indicating an immune-enriched state with enhanced NET-associated transcriptional potential, despite clinical health. In peri-implantitis, this CXCR2+ neutrophil subset expanded further and displayed increased oxidative, chemotactic, and NET-associated programs, supported by tissue validation of MPO, CXCR2, CitH3, and ROS signals. Cell-cell communication analysis nominated fibroblast-derived CXCL signaling as a potential contributor to CXCR2+ neutrophil recruitment. NSUN6, an RNA modification enzyme, was enriched in disease-associated CXCR2+ neutrophils, and NSUN6 knockdown in neutrophil-like cells attenuated CXCR2+ cell enrichment and NET-associated marker expression.

CONCLUSION: Clinically healthy peri-implant mucosa before functional loading is not immunologically equivalent to gingiva, but represents an immune-primed niche that may lower the threshold for inflammatory breakdown. These findings may not be directly generalized to long-term functionally loaded implants. Peri-implantitis is characterized by amplification of an oxidative CXCR2+ neutrophil state, with fibroblast-derived CXCL-CXCR2 signaling and NSUN6-associated neutrophil activation emerging as candidate pathways for future diagnostic and therapeutic investigation.