Table 1.
Summary table of the studies assessing the role of neutrophil extracellular traps (NETs) in periodontitis and the induction of NET formation by periodontal bacteria.
| Studies on the Expression of NETs in Periodontitis Patients | |||||
| Author | Year | Participants | Types of samples | NET marker | Results |
| Zhang et al. [62] | 2020 | 27 periodontitis, 17 gingivitis and 20 controls | Peripheral blood neutrophils | IL-8 and TNF-alpha as NETs inducers | Periodontitis showed lower expression of IL-8 compared to controls |
| Moonen et al. A [61] | 2019 | 1st part:38 periodontitis and 38 controls 2nd part: 91 periodontitis before and after treatment |
Peripheral blood neutrophils | SYTOX Green | No differences in NET degradation between healthy subjects and periodontitis. Periodontal therapy increased NET degradation |
| Magán-Fernández et al. [63] | 2019 | 6 Chronic periodontitis, 5 gingivitis and 2 controls | Gingival tissue biopsies | CitH3 and MPO | Higher H3 in gingivitis and MPO higher in periodontitis |
| Levy et al. [64] | 2019 | 3 Localized aggressive periodontitis and 3 controls and HL60 neutrophils | Peripheral blood neutrophils and HL60 neutrophils incubated with nupharidine | SYTOX Green | NET formation was higher in the neutrophils exposed to Nupharidine |
| Kaneko et al. [65] | 2018 | 40 Rheumatoid arthritis and periodontitis, 30 periodontitis and 43 controls | Serum samples | NET-associated MPO-DNA complexes by ELISA | NETs increased in the RA + periodontitis group. NETs were associated with moderate to severe periodontitis. Periodontal treatment reduced NETs |
| White et al. [60] | 2016 | Chronic periodontitis and controls (40 pairs) | Peripheral blood neutrophils stimulated with PMA or HOCl | SYTOX Green | NET formation decreased and NET removal was restored following periodontal treatment |
| Fine et al. [66] | 2016 | 17 Chronic periodontitis and 11 controls | Blood and oral neutrophils | CitH3, MPO, CD18 | Proinflammatory oral neutrophils from periodontitis showed high levels of NET formation compared to controls |
| Hirschfeld et al. [67] | 2015 | 14 Experimental gingivitis and 6 controls | Supragingival plaque, peripheral blood neutrophils | CitH3, Histone H1, CD-177, MPO, NE, Cathepsin-G. | NETs were found within the oral biofilm. Bacterial isolates tested induced NET formation. |
| Vitkov et al. [68] | 2010 | 26 Periodontitis | GCF (18); Purulent crevicular exudate (8) | Scanning electron microscopy (SEM); CitH3 and DNA | All neutrophils in the samples were citrullinated. 78% of them showed dispersed NETs |
| Vitkov et al. [69] | 2009 | 22 Chronic Periodontitis | Purulent crevicular exudate (22); Gingival biopsies (12) | Exudates: NE and DNA; Biopsies: Transmission electron microscopy (TEM) and SEM (with and without DNase). |
NETs were found on all the exudate samples. DNase caused the disappearance of NETs |
| In Vitro Studies on NET Formation Induced by Periodontal Bacteria | |||||
| Author | Year | Participants | Types of samples | NET marker | Results |
| Bryzek et al. [55] | 2019 | Human donors | Peripheral blood neutrophils stimulated with different P. gingivalis strains, antigens and gingipains | NE, Hoechst 33342, ADNbc PicoGreen® and DNase I | Gingipains from P. gingivalis induce NETs formation and prevent P. gingivalis entrapment and killing |
| Alyami et al. [70] | 2019 | In vitro PMN layers | Human primary neutrophils infected with Aggregatibacter actinomycetemcomitans, P. gingivalis and F. nucleatum | SYTOX Orange, NE, CitH3, DAPI | F.nucleatum induced rapid and robust NET formation trough NOD1 and NOD 2 receptors |
| Hirschfeld et al. [71] | 2017 | 10 Healthy donors | Peripheral blood neutrophils. Stimulation with 19 periodontal bacteria | FITC NET-DNA, NE, and MPO | Certain species stimulated higher NET formation. |
| Doke et al. [57] | 2017 | Healthy donors | PMA-stimulated peripheral blood neutrophils. Nucleases from several periodontal bacteria. | SYTOX Orange, NE and DAPI | Prevotella intermedia demonstrated the highest NET degradation of all the Gram—periodontal bacteria |
| Roberts et al. [72] | 2016 | 5 Papillon–Lefévre syndrome (PLS) patients and 5 controls | Peripheral blood neutrophils stimulated with periodontal bacteria | SYTOX Green, NE, NET-bound MPO, NET-bound CG | Neutrophils from PLS patients have a reduced capacity for NET formation and a compromised antimicrobial activity |
| Palmer et al. [73] | 2016 | Healthy donors | Peripheral blood neutrophils incubated with oral bacteria in different complement blocking conditions | NET-DNA fluorometry | Complement and IgG enhance NET formation by several periodontal bacteria |
| Hirschfeld et al. [74] | 2016 | Healthy donors | Peripheral blood neutrophils with A.a., A.a. leucotoxin | Micrococcal nuclease | The leucotoxic strain of A.a. and high concentrations of A.a. leucotoxin induced NET formation |
| Jayaprakash et al. [56] | 2015 | Healthy donors | In vitro PMA-generated NETs; | FITC-labeled P. gingivalis, F-actin, DNA | P. gingivalis strains K1A and E8 induced NET formation |
| Palmer et al. [54] | 2012 | Healthy donors | In vitro PMA-generated NETs | DNase activity of periodontal bacterial species. SYTOX Green | DNase producing species caused the degradation of NETs |
| Other Studies Regarding NET Formation in Oral Neutrophils | |||||
| Moonen et al. [18] | 2019 | 9 Healthy donors | PMA-stimulated venous blood neutrophils and oral neutrophils | SYTOX Green | Oral neutrophils showed greater NET formation than circulating neutrophils in both stimulated and non-stimulated groups |