The Role of IL-17 in Periodontitis and Its Systemic Connections.

Interleukin 17 (IL-17) is a crucial mediator at the interface of periodontal dysbiosis and host immunity. This review synthesizes current evidence on IL-17 in periodontitis (PD), its systemic connections, and the role of IL-17 gene variants. Clinical and experimental studies show that IL-17 rises in periodontal disease and is associated with the severity of PD via action on epithelial, stromal and osteoblastic cells to promote chemokine release, neutrophil recruitment, cyclooxygenase 2 and prostaglandin E2 synthesis, RANKL expression, osteoclastogenesis, and matrix metalloproteinase activity. Periodontopathogens Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans pre-activate the local inflammation-maintaining Th17 response. There is converging evidence linking IL-17-centered signaling with rheumatoid arthritis, diabetes mellitus, and psoriasis in favor of a shared inflammatory network in barrier tissues and synovium. Despite these associations, IL-17 biology is contextually determined with mucosal defense and bone homeostatic roles that caution against unidimensional explanations. Evidence on IL-17A and IL-17F polymorphisms is still heterogeneous across populations with modest and variable risk associations with PD. Clinically, IL-17 in gingival crevicular fluid, saliva, or serum is a potential monitoring biomarker when utilized along with conventional indices. Therapeutically, periodontal therapy that reduces microbial burden may inhibit IL-17 function, and IL-17-targeted therapy has to balance potential benefit to inflammation and bone resorption against safety in oral tissues. The following research must utilize harmonized case definitions, standardized sampling, and multiethnic cohorts, and it must include multiomics to be able to differentiate between causal and compensatory IL-17 signals.