Gingival Toll-like receptor and cytokine mRNA expression in equine periodontitis and oral health

Objectives: Equine periodontitis is a common and painful condition, causing severe pain and eventual tooth loss. Despite this, the disease often goes unnoticed by owners and is thus a major welfare concern. The aetiopathogenesis of the condition remains relatively poorly understood with few recent studies performed. The innate immune system is known to play an important role in human periodontitis, however its role in equine periodontitis has not been examined. The aim of this study was to quantify the expression levels of Toll-like receptor (TLR) and cytokine mRNAs in gingival tissue from orally healthy horses and those affected by periodontitis.
Methods: Gingival tissue samples were taken post-mortem from seven orally healthy horses and thirteen horses with periodontitis. mRNA expression of TLR2, TLR4 and TLR9 and cytokines IL-1β, TNFα, IL-4, IL-6, IL-10, IL-12, IL-17 and IFN-γ was determined using qPCR. Statistical significance of results was assessed using f-tests and paired t-tests.
Results: All TLRs and cytokines showed up-regulation of mRNA expression in disease. However, statistically significant increases were noted in expression of mRNAs for TLR2 (p=0.005), TLR4 (p=0.03) and TLR9 (p=0.0001) and cytokines IL-1β (p=0.02), IL-4 (p=0.03), IL-6 (p=0.005), IL-10 (p=0.005), IL-12 (p=0.02), and IFN-γ (p=0.003). The fold change between oral health and periodontitis was largest for IFN-γ, which increased 53-fold in disease.
Conclusions: This study has provided an initial insight into the involvement of the innate immune system in equine periodontitis. Increased expression of TLR2 and TLR9 mRNAs indicates increased need for recognition of and response to microbial products and bacterial DNA in disease. Increased expression of mRNAs for pro-inflammatory, anti-inflammatory and Th1/Th2/Th17cytokines indicates a complex immune response to periodontal pathogens. Further studies are required to fully characterise the role of the innate immune system in equine periodontitis.