IL-17 and IL-23 Affect Inflammation in the TMJ

Objectives: The recent discovery of a distinct lineage of T helper cells, Th17 cells, has provoked breakthroughs in understanding rheumatoid arthritis (RA) pathology.  Interleukin-17 (IL-17) release from TH17 cells has been studied in animal models of experimentally-induced arthritis in joints of the extremities.  In addition, IL-23 is a key cytokine that is involved in the process of unraveling the distinct lineage of Th17 cells from the Th1/Th2 scheme.  However, our understanding of IL-17 and IL-23 activity in RA of the TMJ is minimal.  Thus, the objectives of our study were to investigate the role of IL-17 on IL-23 expression during TMJ inflammation using a complete Freund’s adjuvant (CFA) -induced model and determine if a neutralizing antibody treatment would reduce damage and inflammation.

Methods: Fifty-six rats were randomly divided into seven groups of eight: no treatment (NT), then CFA-only treatment (CFA), IL-17 antibody-only treatment (IL), or CFA+IL-17 antibody (CFA+IL) for two time periods each, either two or seven days.  For antibody neutralization experiments, anti-IL-17 antibody was injected into rats on days 1 and 6 following the CFA injection. The rats were sacrificed and TMJ tissues were extirpated bilaterally, homogenized, and then analyzed. Quantitative measurement of IL-17 and IL-23 was performed in duplicate using ELISA.

Results: Histological analysis revealed a high inflammatory response in the CFA-only-treated groups and a significantly decreased response in the CFA+IL-17 antibody-treated groups.  ELISA revealed increased levels of IL-17 and IL-23 in the inflamed TMJ (p≤0.05).  Neutralizing antibody treatment produced a significant reduction in both IL-17 and IL-23 levels (p≤0.05).

Conclusions:

This study demonstrated that IL-17 plays a vital role in the cascade of TMJ inflammation, potentially through the activation of IL-23, and that anti-IL-17 treatment may be a potential therapeutic treatment for those with TMJ disorders. Supported by the Baylor Oral Health Foundation.