Interleukin-34 in Stage I and II Periodontitis

Periodontal disease is a multifactorial infection induced by a complex of bacterial species that interact with host tissues and cause destruction of the periodontal structures, including the supporting tissues of the teeth, alveolar bone, and periodontal ligament.

The bacterial biofilm formation initiates gingival inflammation; however, periodontitis initiation and progression depend on dysbiotic ecological changes in the microbiome in response to nutrients from gingival inflammatory and tissue breakdown products that enrich some species and anti-bacterial mechanisms that attempt to contain the microbial challenge within the gingival sulcus area once the inflammation has initiated.

Current evidence supports multifactorial disease influences, such as smoking, diabetes mellitus, obesity, metabolic syndrome, osteoporosis, low dietary calcium and vitamin D and other immunoinflammatory responses that make the dysbiotic microbiome changes more likely for some patients than others and likely influence the severity of disease for such individuals.

During periodontitis, the pathogen triggers the white blood cells of the innate immune system to release proinflammatory mediators such as cytokines that play a vital role in the progression of the inflammation process of periodontitis. In addition, these pathogens can activate the acquired immune system contributing to the release of more cytokines and chemokines that cause permanent bone damage and irreversible periodontal attachment loss.

Cytokines are defined as soluble small proteins (~5-20 kDa) that bind to specific receptors on certain cells, stimulate some internal cellular changes, and cause multiple genetic and chemical regulations.

There are two different types of inflammatory cytokines: proinflammatory cytokines that are involved in inflammatory reactions including interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF-α), and anti-inflammatory cytokines that regulate or control the pro-inflammatory cytokine response including interleukin-4 (IL-4), interleukin-1 receptor antagonist (IL-1RA) and interleukin-10 (IL-10).

NSPT aimed at the mechanical removal of bacterial plaque from the tooth surface is considered the "gold standard." This procedure decreases the number of Gram-negative bacteria in favor of Gram-positive bacteria as well as reduces the overall number of microorganisms in periodontal pockets and decreases the amount of proinflammatory cytokines.

Recent methods in oral and periodontal disease diagnostic research are identifying periodontal risk which is quantified by objective measures like biomarkers which are diagnostic tools to measure periodontal disease at the molecular, cellular, tissue, and clinical levels. The biological media for detecting periodontal disease biomarkers include GCF, saliva, serum, subgingival plaque, and tissue biopsies.

The major attraction of GCF as a diagnostic marker is the site-specific nature of the sample which may offer the basis for patient-specific diagnostic tests for periodontal disease. Moreover, the simplicity of its use along with a level of reliability and low cost favors its use over other modalities.

The discovery of new biomarkers will aid in the development of new therapeutic approaches via host modulatory drugs for periodontal disease treatment leading to more individualized, targeted treatments for oral health.

In 2008, Lin identified a secreted protein known as IL-34 with a high functional selectivity represented by stimulating monocyte survival in a CSF-1R-dependent manner. Many studies provided insight into IL-34 biology, but many questions remain unanswered, specifically in terms of its function.

High expression of IL-34 correlates with disease severity in autoimmune diseases (Sjögren's syndrome, SLE, and RA), and inflammatory diseases (liver fibrosis, kidney disease, and inflammatory bowel disease). In contrast, IL-34 plays a protective role in some diseases, such as atopic dermatitis, Alzheimer's disease, breast cancer, and head and neck cancer.

In periodontal disease, some studies such as Guruprasad \& Pradeep in 2018 and Bozkurt Doğan in 2021 suggested that IL-34 is a proinflammatory cytokine in the pathogenesis of periodontal disease while others such as Martinez in 2017 and Lira-Junior in 2021 concluded that IL-34 play a protective role in periodontal disease.

Therefore, Further studies must be carried out to confirm these findings and to better understand the possible role of IL-34 in the pathogenesis of periodontal diseases and to evaluate its levels in GCF in patients with periodontal disease after NSPT