Immune Cells and Molecular Networks in Experimentally Induced Pulpitis

Abstract

Dental pulp is a dynamic tissue able to resist external irritation during tooth decay by using immunocompetent cells involved in innate and adaptive responses. To better understand the immune response of pulp toward gram-negative bacteria, we analyzed biological mediators and immunocompetent cells in rat incisor pulp experimentally inflamed by either lipopolysaccharide (LPS) or saline solution (phosphate-buffered saline [PBS]). Untreated teeth were used as control. Expression of pro- and anti-inflammatory cytokines, chemokine ligands, growth factors, and enzymes were evaluated at the transcript level, and the recruitment of the different leukocytes in pulp was measured by fluorescence-activated cell-sorting analysis after 3 h, 9 h, and 3 d post-PBS or post-LPS treatment. After 3 d, injured rat incisors showed pulp wound healing and production of reparative dentin in both LPS and PBS conditions, testifying to the reversible pulpitis status of this model. IL6, IL1-β, TNF-α, CCL2, CXCL1, CXCL2, MMP9, and iNOS gene expression were significantly upregulated after 3 h of LPS stimulation as compared with PBS. The immunoregulatory cytokine IL10 was also upregulated after 3 h, suggesting that LPS stimulates not only inflammation but also immunoregulation. Fluorescence-activated cell-sorting analysis revealed a significant, rapid, and transient increase in leukocyte levels 9 h after PBS and LPS stimulation. The quantity of dendritic cells was significantly upregulated with LPS versus PBS. Interestingly, we identified a myeloid-derived suppressor cell-enriched cell population in noninjured rodent incisor dental pulp. The percentage of this population, known to regulate immune response, was higher 9 h after inflammation triggered with PBS and LPS as compared with the control. Taken together, these data offer a better understanding of the mechanisms involved in the regulation of dental pulp immunity that may be elicited by gram-negative bacteria.

Ageing affects the proliferation and mineralization of rat dental pulp stem cells under inflammatory conditions

“…It has been reported that when 5 μL of 10 mg mL −1 LPS was injected into rat incisor pulp chamber, inflammatory cell infiltration started 9 h later and the inflammation was limited to the corners of the pulps and disappeared after 3 days (Renard et al . ). Analogously, in previous study no obvious necrosis was observed, but significant vasodilation occurred in the pulp tissues of juvenile and adult rats after 0.5 μg mL −1 LPS injection for 48 h, and IL‐1β expression increased more strongly in adult than in juvenile inflammatory pulp tissues.…”

“…Since they have a stronger healing capacity after injury than mammalian permanent teeth, the dental pulp of rat incisors provides a convenient model for exploring pulp damage repair (Zheng et al 2009). It has been reported that when 5 lL of 10 mg mL À1 LPS was injected into rat incisor pulp chamber, inflammatory cell infiltration started 9 h later and the inflammation was limited to the corners of the pulps and disappeared after 3 days (Renard et al 2016). Analogously, in previous study no obvious necrosis was observed, but significant vasodilation occurred in the pulp tissues of juvenile and adult rats after 0.5 lg mL À1 LPS injection for 48 h, and IL-1b expression increased more strongly in adult than in…”

“…Experimentally LPS‐induced pulpitis models have been adopted to explore immune cells and network molecules in pulpitis (Renard et al . ). In addition, LPS‐induced inflammation has been used to detect changes in the biological characteristics, including proliferation, osteogenic, migration and adhesion of DPSCs (Liu et al .…”

“…As the stages of inflammation are difficult to synchronize with a natural infection, in order to objectively assess inflammation, stimulation with LPS is widely used to simulate the inflammatory microenvironment in vivo or in vitro. Experimentally LPS-induced pulpitis models have been adopted to explore immune cells and network molecules in pulpitis (Renard et al 2016). In addition, LPS-induced inflammation has been used to detect changes in the biological characteristics, including proliferation, osteogenic, migration and adhesion of DPSCs (Liu et al 2014, He et al 2015.…”

Management of deep caries and the exposed pulp

“…) and in vivo studies (Renard et al . ) have demonstrated changes in cellular transcription and protein expression when inflamed. Furthermore, cells cultured in mineralizing, angiogenic and neurogenic culture conditions express a range of extracellular molecules, which promote an autocrine and paracrine healing response (Duncan et al .…”