OR12 - The Immunomodulatory Effects of Lipopolysaccharide on Stem Cells of the Apical Papilla

Stem cells of the apical papilla (SCAP) play an important role in regenerative endodontic procedures (REPs). Previous research has demonstrated that gram-negative bacteria predominate infected root canal systems and can activate the immune system, causing cytotoxicity to SCAP. Lipopolysaccharide (LPS), a major component of gram-negative bacteria, could be present in the canal even after bacteria are eliminated, possibly affecting SCAP. Studies have shown that SCAP upregulates TLR4 in the presence of LPS. This upregulation could possibly activate the innate immunity system. However, the immunomodulatory properties of LPS-treated SCAP have not been clearly elucidated. Hence, the aim of this study is to evaluate the interactions of SCAP pretreated with and without LPS with the immune system. Human SCAP were cultured and pretreated with or without LPS and then co-cultured with human peripheral blood mononuclear cells (PBMCs). PBMCs in culture were activated with recombinant IL-2. An enzyme-linked immunosorbent assay (ELISA) was performed to measure levels of pro-inflammatory cytokines for these co-cultures. Data was analyzed using an ANOVA with post-hoc Tukey test. SCAP pretreated with LPS induced higher levels of pro-inflammatory cytokines, namely IL-6 and TNF-α, when co-incubated with both non-activated and activated PBMCs. SCAP by itself also secreted IL-6 in the presence of LPS. SCAP treated with LPS activates the innate immunity system to secrete increased levels of pro-inflammatory cytokines like IL-6 and TNF-α. This suggests that the presence of LPS in the canal could have negative effects on REPs. Adequate disinfection and neutralization of LPS is necessary for a successful REP.