The Multifaceted Role of IL-35 in Periodontal Disease and Beyond: From Genetic Polymorphisms to Biomarker Potential

Periodontitis is a prevalent chronic inflammatory disease with complex etiopathogenesis involving microbial dysbiosis, host immune response, environmental factors, and genetic susceptibility. Among the cytokines implicated in periodontal immunoregulation, interleukin-35 (IL-35) has emerged as a novel anti-inflammatory mediator with potential diagnostic and therapeutic relevance. This narrative review evaluates the role of IL-35 in periodontal disease by exploring its local and systemic expression, response to non-surgical periodontal therapy (NSPT), and association with clinical disease severity. Additionally, current evidence regarding IL-35 gene polymorphisms and their potential contribution to individual susceptibility and disease progression, as well as their relevance in related systemic conditions, is assessed. A comprehensive review and synthesis of recent clinical and experimental studies were conducted, focusing on IL-35 levels in saliva, serum, and gingival crevicular fluid (GCF) among patients with healthy periodontium, gingivitis, and various stages of periodontitis, both before and after NSPT. Emphasis was placed on longitudinal studies evaluating IL-35 dynamics in correlation with periodontal parameters, as well as genetic association studies investigating IL-12A and EBI3 gene polymorphisms. IL-35 levels were generally found to be higher in healthy individuals and reduced in periodontitis patients, indicating a possible protective role in maintaining periodontal homeostasis. Following NSPT, IL-35 levels significantly increased, corresponding with clinical improvement and reduced inflammatory burden. Genetic studies revealed variable associations between IL-35 polymorphisms and susceptibility to periodontitis and related systemic conditions, although further research is needed for validation. IL-35 appears to function as a modulator of immune resolution in periodontal disease, with potential utility as a non-invasive biomarker for disease activity and therapeutic response. Its upregulation during periodontal healing supports its role in promoting tissue stabilization. The integration of cytokine profiling and genetic screening may enhance personalized risk assessment and targeted interventions in periodontal care.