Regulation of PGLYRP1 and TREM-1 during Progression and Resolution of Gingival Inflammation

Introduction: The triggering receptor expressed on myeloid cells 1 (TREM-1) signaling pathway is stimulated by bacteria and, together with its putative ligand peptidoglycan recognition protein 1 (PGLYRP1), propagates proinflammatory responses. Objectives: We aimed to evaluate the TREM-1/PGLYRP1/interleukin (IL)-1 beta regulation in response to biofilm accumulation and removal in an experimental human gingivitis model. Methods: The study (n = 42 participants, mean age: 23.8 +/- 3.7 y) comprised a recruitment step (day -14) followed by experimentally induced biofilm formation (induction [I] phase, day 0 to +21) and a 2-wk resolution (R) phase (day +21 to +35). Plaque was recorded by the Modified Quigley and Hein Plaque Index (TQHPI), while records of gingival inflammation were based on the Modified Gingival Index (MGI). Unstimulated whole saliva supernatants (n = 210, 5 time points) were tested for TREM-1, PGLYRP1, and IL-1 beta by enzyme-linked immunosorbent assay. Results: During the I-phase, concentrations of all analytes showed a tendency for downregulation at day +7 compared to day 0. TREM-1 (P = 0.019) and PGLYRP1 (P = 0.007) increased significantly between day +7 and day +21. Although all analyte levels decreased during the R-phase, the difference was not significant except TREM-1 being at borderline significance (P = 0.058). Moreover, TREM-1, PGLYRP1, and IL-1 beta showed significant positive correlations (P < 0.0001) with each other. The study participants were grouped into fast and slow responders based on clinical gingival inflammation scores. At each time point, fast responders showed significantly higher concentrations of TREM-1 (P < 0.025), PGLYRP1 (P < 0.007), and IL-1 beta (P < 0.025) compared to slow responders. Mixed-effects multilevel regression analyses revealed that PGLYRP1 (P = 0.047) and IL-1 beta (P = 0.005) showed a significant positive association with the MGI scores. Conclusion: The study demonstrated that TREM-1 and PGLYRP1 are regulated in response to biofilm accumulation and removal, and fast responders demonstrated higher levels of these analytes compared to slow responders. Knowledge Transfer Statement: The results of this study demonstrated the suitability of salivary TREM-1 and PGLYRP1 to reflect biofilm accumulation and removal and PGLYRP1 to monitor the progression and resolution of inflammation in gingivitis-susceptible individuals (fast responders). Combined with conventional risk factors, the molecular toolbox proposed here should be further validated in future studies to confirm whether it can be used for population-based monitoring and prevention of gingivitis.