Regulation of TREM-1/PGLYRP1/IL-1β Axis During Experimental Gingivitis

Objectives: The Triggering Receptor Expressed on Myeloid cells 1 (TREM-1) is a cell surface receptor of the immunoglobulin superfamily, involved in the propagation of the inflammatory response to bacterial challenge. TREM-1 and its putative ligand PGLYRP1 were shown to be associated with periodontitis. The present study aimed to investigate the levels of TREM-1, PGLYRP1, IL-1β in saliva samples during the induction (I) and resolution (R) phases of experimental gingivitis.
Methods: Forty-two systemically healthy, non-smoker participants (23.8yrs±3.7) were recruited. Experimental gingivitis was induced over 21 days, followed by a two-week resolution phase. For each subject, a modified gingival index (GI), modified Quigley-Hein plaque index (PI) were recorded. Unstimulated whole saliva (n=210) was collected at Day 0, 7, 14 and 21 (I-phase), and at Day 35 (R-phase). TREM-1, PGLYRP1 and IL-1β were measured by ELISA. For statistical analysis, Dunn’s multiple comparison (Friedman) and spearman rank correlation test was used (p<0.05).
Results: Mean PI and GI increased in the I-phase from 0.1±0.1 to 3.0±0.4 (p<0.001) and from 0.02±0.02 to 1.93±0.3 (p<0.001), respectively. Pl and GI decreased during the R-phase, reaching levels similar to Day 0 (p<0.001). TREM-1, PGLYRP1 and IL-1β were detected in 95% of all samples and concentrations (mean±SD) increased significantly during the I-phase (Day7 vs Day21) from 346.3±340.3pg/mL to 415.2±322.2pg/mL (p=0.019) for TREM-1 and from 16.2±17.0ng/mL to 20.9±17.7ng/mL (p=0.0072) for PGLYRP1. A decrease in concentration was observed during the R-phase (Day21 vs Day35) for all three analytes but the differences did not reach to significance, nevertheless the difference for TREM-1 was at the border of significance (p=0.0578). Further, time-independent analysis showed significant positive correlations between all three analytes (p<0.0001).
Conclusions: Increasing levels of TREM-1, PGLYRP1 and IL-1β while inducing gingivitis experimentally and decreased levels after reintroducing oral hygiene measures indicate that this axis can be used for monitoring active gingival inflammation.