Oral tissues are constantly exposed to various types of damage – mechanical (during food intake), microbiological (during the penetration of pathogenic bacteria, fungi, viruses). In healthy oral tissues, there is a balance between commensal bacteria and innate immune cells, primarily neutrophils. When this balance is disturbed, an inflammatory process develops.
If the number of neutrophils is insufficient, the restraining effect of the oral immune system is reduced. However, if the neutrophil response is excessive, this will also (due to an increase in secondary alteration) lead to an inflammatory process in the periodontium, manifested by the development of a chronic inflammatory disease – periodontitis, accompanied by the destruction of the supporting tissues of the tooth, periodontium, alveolar bone and, as a consequence, tooth loss. In severe cases, this increases the risk of developing atherosclerosis, rheumatoid arthritis, diabetes mellitus, etc.
During the development of this pathological process, circulating neutrophils are quickly mobilized to the site of infection or inflammation through transmigration.
This process begins with the expression of adhesion receptors (E- and P-selectins) by endothelial cells. Then neutrophils must be activated by chemokines, which increases their affinity for integrins and ensures strong adhesion of polymorphonuclear leukocytes to endothelial cells, which serves as a necessary condition for transmigration. This process is primarily regulated by heterodimeric receptors formed by either the α subunit (CD11) or the common β subunit (CD18). These receptors interact with adhesion ligands such as intercellular adhesion molecule-1 and -2 on endothelial cells.
Neutrophils are equipped with various antimicrobial mechanisms that help them fight a wide range of microorganisms. These responses include phagocytosis, activation of oxidative stress, degranulation, and formation of neutrophil extracellular traps.
It has been shown that the number of polymorphonuclear leukocytes increases in the oral fluid as the disease develops. However, their role in the pathogenesis of chronic periodontitis is not completely clear, which determines the relevance of this problem.
An indicator of cell activity is the number of microvesicles necessary to ensure information flows in tissues. The total number of microvesicles in patients with chronic periodontitis increased more than 11 times (Table 2; 0.000001), and to a greater extent due to microvesicles of leukocyte origin. Thus, in healthy people, microvesicles formed by all leukocytes accounted for 29.5%, in case of periodontal inflammation – 41.15%, more than a third of them were formed by neutrophils. About 56% of neutrophil microvesicles had the CD11b marker, which indicated the formation of strong adhesion of neutrophils to the vascular endothelium and their active migration into damaged tissues.
When studying the level of neutrophil aggression factors, their increase in patients with periodontitis was revealed. The minimum increase in the indicator was recorded in myeloperoxidase – its concentration in the oral fluid of patients with periodontitis increased by 2.1 times, and the maximum – in metalloproteinase-2: its level increased by 24.8 times (0.0001)
Table. Factors of neutrophil aggression in the oral fluid of patients with chronic periodontitis
|
Indicators |
Patients periodontitis, n=30 |
р |
|
|
Calprotectin MRPg8/14, pg/ml |
15.89 (8.90; 19.05) |
62, 37 (47.98; 104.56) |
0.00002 |
|
Lipocaine 2 NGAL, pg/ml |
1.90 (1.40; 2.40) |
7.90 (7 ,30; 8.40) |
0.0001 |
|
Matrix metalloproteinase-9, pg/ml |
11.02 (5.03; 14.99) |
58.05 (54.87; 61.24) |
< p>0.00004 |
|
Myeloperoxidase, ng/mg protein |
28.45 ( 17.86; 33.61) |
58.21 (57.04; 60.98) |
0, 0001 |
Objective indicators of the oral health of the study group also had a strong positive relationship with factors of aggression of polymorphonuclear leukocytes. For example, the content of metalloproteinase-2 was correlated with the depth of the periodontal pocket (r=0.754), bleeding index (r=0.811), PMA (r=0.675); myeloperoxidase indicator – with the same parameters (r=0.721, r=0.689 and r=0.799, respectively) as the calprotectin concentration (r=0.654, r=0.743 and r=0.901, respectively).
The main causative factor of periodontitis is considered to be colonization of the oral biofilm by opportunistic bacteria. It is believed that P. gingivalis is the main causative agent of periodontitis. It has been shown that oral bacteria alone are not sufficient for the development of periodontitis. The clinical picture of periodontitis is the result of an exaggerated inflammatory response of the body in response to bacterial load, which leads to periodontal damage.
Neutrophils are the most abundant white blood cells in periodontal pockets, gingival crevice, and inflamed periodontal tissues. In healthy periodontal tissues, neutrophils are mainly found in the connective epithelium and gingival fluid; they are necessary to maintain the symbiosis between the bacterial community and the macroorganism.
The initiation and progression of periodontitis depends on dysbiotic changes in the microbiome in response to the emergence of nutrients from the products of gingival inflammation and tissue breakdown, as well as antibacterial mechanisms by which the body attempts to reduce the microbial load in the gingival crevicular area after the onset of inflammation. The body's reaction to damage is the activation of the innate part of the immune system, where the neutrophil is one of the main defenders.
During the development of the inflammatory process, there is an increase in the number of neutrophils and the intensity of their migration into the gingival crevice. Their release of proteolytic and collagenolytic enzymes, as well as reactive oxygen species in periodontal tissues leads to loss of marginal periodontal ligament fibers, apical migration of the connective epithelium, which contributes to the apical spread of bacterial biofilm along the root surface and even greater inflammation.
Polymorphonuclear leukocytes, through the formation of microvesicles carrying, on the one hand, aggression factors aimed at eliminating the pathogen, and on the other, chemokines that induce the recruitment of cells and innate and adaptive immunity, cause an increase in secondary alteration and prolongation of inflammation.
The intense struggle of neutrophils with pathogenic microflora leads to the appearance of neoantigens at the site of damage and the launch of the autoimmune component of the inflammatory process. In addition, activated neutrophils can induce osteoclastic bone resorption through the expression of a key osteoclastogenic cytokine, membrane-bound receptor activator of nuclear factor-κB ligand. As a result, a self-sustaining inflammatory process is formed, chronic inflammation develops, leading to the destruction of periodontal tissue.
Neutrophils enhance the pathogenesis of chronic periodontitis due to the secretion of aggression factors: metalloproteinases, myeloperoxidase, calprotectin, lipocaine 2 and microvesicles.