Platelet activation and platelet-leukocyte interaction in generalized aggressive periodontitis

Generalized aggressive periodontitis (GAgP) is an inflammatory disease of host response to bacterial challenge. To explore the role of platelets in host-microbial interactions in patients with periodontitis, 124 patients with GAgP and 57 healthy subjects were enrolled. Reliable indicators of subclinical platelet functional status, platelet count (PLT), platelet large cell ratio (PLCR), and mean platelet volume (MPV), were significantly lower in the GAgP group than in the control group and were negatively correlated with clinical periodontal parameters. The levels of important cytosolic protein in neutrophils, calprotectin (S100A8/A9) in plasma, and gingival crevicular fluid (GCF) were significantly higher in patients with GAgP compared with healthy subjects. Moreover, the GCF calprotectin level was negatively correlated with PLCR and MPV values. To explore the possible mechanisms of changes in platelet indices in periodontitis, flow cytometry analysis was performed, and patients with GAgP were found to have a higher status of platelet activation compared with healthy controls. Porphyromonas gingivalis (P. gingivalis) and recombinant human S100A8/A9 (rhS100A8/A9) induced platelet activation and facilitated platelet-leukocyte aggregate formation in whole blood of healthy subjects. In response to P. gingivalis and rhS100A8/A9, platelets from patients with GAgP increased activation and increased formation of platelet-leukocyte aggregates compared with those from healthy subjects. Platelet aggregates and platelets attached to leukocytes were found on gingival tissues from patients with GAgP, suggesting that decreased platelet size and count in the circulation might be related to consumption of large, activated platelets at inflamed gingiva. Platelets may have a previously unrecognized role in host response to periodontal infection.