The role of miR-155 and IL-6 in the shared pathogenesis of periodontitis and rheumatoid arthritis: a cross-sectional case-control study

Purpose: Periodontitis (PD) and rheumatoid arthritis (RA) share inflammatory pathways, with interleukin-6 (IL-6) and microRNA-155 (miR-155) implicated as key mediators.This study quantified salivary IL-6 and serum miR-155 levels across 4 groups (PD only, RA only with a healthy periodontium, comorbid PD+RA, and healthy controls) and examined their associations with clinical severity indices of both diseases.Methods: This cross-sectional case-control study enrolled 120 participants (30 per group).Periodontitis was diagnosed according to the 2017 American Academy of Periodontology/ European Federation of Periodontology classification, and RA was diagnosed according to the 2010 American College of Rheumatology/European League Against Rheumatism criteria.Salivary IL-6 and serum miR-155 were measured using quantitative real-time polymerase chain reaction.Results: Combined salivary IL-6 and serum miR-155 expression differed significantly across groups (multivariate analysis of covariance, Pillai's trace=0.892,P<0.001), with the highest levels observed in the comorbid group.Both biomarkers showed strong positive correlations with periodontal clinical parameters (Spearman =0.704-0.958)and moderate-to-strong correlations with RA disease activity measures (=0.391-0.782;all P<0.001).The periodontal severity composite score explained 94.3% of the variance and correlated most strongly with .Receiver operating characteristic analyses yielded area under the curve (AUC) values of 0.75-1.00,including perfect discrimination (AUC=1.00) in multiple comparisons.Conclusions: Salivary IL-6 and serum miR-155 were strongly associated with the presence and severity of both PD and RA and were markedly elevated in comorbid cases, supporting their potential as biomarkers.Longitudinal studies are needed to establish temporality and causality.