Presence of langerhans cells, regulatory T cells (Treg) and mast cells in asymptomatic apical periodontitis

The Mystifying Role of Mast Cells in the Pathogenesis of Periapical Pathologies - a Systematic Review

INTRODUCTION

Oral periapical lesions present a significant global health burden, with their pathogenesis shrouded in complexity due to multifaceted mechanisms. Despite extensive research, the precise role of mast cells in their pathogenesis remains elusive. The present systematic review aimed to elucidate the mechanism of mast cells in the immunopathology of periapical lesions.

METHODS

An extensive literature search conducted across databases (MEDLINE via PubMed, Scopus, Cochrane Library, and EMBASE and gray literature) of original research articles that examined the role of mast cells in periapical lesions were investigated and selected for review. The risk of bias for each study was meticulously assessed using the QUADAS-2, and Review Manager 5.4 (RevMan v5.4, The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark) was utilized to generate the results.

RESULTS

A total of 41 published articles were included for data synthesis. The findings revealed significant variations in mast cell number within the fibrous capsule of periapical granuloma and periapical cyst, with notably elevated counts in the latter. Periapical granuloma manifested a predominance of granulated mast cells in the subepithelial region. In contrast, the periapical cyst exhibited a preponderance of degranulated mast cells in the deeper areas of the capsule.

CONCLUSIONS

The current evidence substantiates that mast cells play a crucial role in the pathogenesis, progression, fibrosis, and chronicity of periapical lesions.

Correlation between PD-1/PD-L1 and RANKL/OPG in chronic apical periodontitis model of Sprague-Dawley rats

Chronic apical periodontitis (CAP) is characterized by inflammation and destruction of the apical periodontium that is of pulpal origin, appearing as an apical radiolucent area, and does not produce clinical symptoms. Little is known about whether the PD-1/PD-L1 ratio is associated with the balance between RANKL and OPG in CAP. The relationship between PD-1/PD-L1 and RANKL/OPG in CAP is investigated in this study. A CAP rat model was established using Sprague-Dawley rats. The pulp chambers were exposed to the oral cavity to allow bacterial contamination. The apical tissues of the bilateral mandibular first molars were analyzed for histological morphology using hematoxylin and eosin (H&E) staining. Immunohistochemistry and qRT-PCR were used to determine the expression of PD-1, PD-L1, OPG, and RANKL mRNA and proteins in periapical tissues and mandibular samples, respectively. The radiological images indicated a poorly defined low-density shadow and alveolar bone resorption after periodontitis induction. Histological analysis revealed an infiltration of inflammatory cells and alveolar bone resorption in the periapical tissues. Mandibular mRNA and periapical protein expression of PD-1, PD-L1, and RANKL was upregulated 7-28 days after periodontitis induction, while the expression of OPG was downregulated. No significant relationship was observed between PD-1/PD-L1 and RANKL/OPG at either mRNA or protein levels in CAP. There is an increased expression of PD-1, PD-L1, and RANKL and a decreased expression of OPG, indicating progression of CAP.

Protective Actions in Apical Periodontitis: The Regenerative Bioactivities Led by Mesenchymal Stem Cells

Resulting from bacterial infection, apical periodontitis (AP) is a common inflammatory disease of the periapical region of the tooth. The regeneration of the destroyed periapical alveolar bone and the surrounding periodontium tissues has long been a difficult task in clinical practice. These lesions are closely related to pathogen invasion and an overreactive immune response. It is worth noting that the protective healing process occurs simultaneously, in which mesenchymal stem cells (MSCs) have a crucial function in mediating the immune system and promoting regeneration. Here, we review the recent studies related to AP, with a focus on the regulatory network of MSCs. We also discuss the potential therapeutic approaches of MSCs in inflammatory diseases to provide a basis for promoting tissue regeneration and modulating inflammation in AP. A deeper understanding of the protective action of MSCs and the regulatory networks will help to delineate the underlying mechanisms of AP and pave the way for stem-cell-based regenerative medicine in the future.

Interplay of collagen and mast cells in periapical granulomas and periapical cysts: a comparative polarizing microscopic and immunohistochemical study

Objectives

This pilot study aimed to establish the interrelationship between collagen and mast cells in periapical granulomas and periapical cysts.

Materials and Methods

An observational cross-sectional study was conducted on the paraffin-embedded tissue sections of 68 specimens (34 periapical granulomas and 34 periapical cysts). The specimens were stained with picrosirius to observe collagen fiber birefringence and anti-tryptase antibody to evaluate the mast cell count immunohistochemically. The mean number and birefringence of collagen fibers, as well as the mean number of mast cells (total, granulated, and degranulated), and the mean inflammatory cell density were calculated. The data obtained were analyzed using the Kruskal Wallis test, Mann Whitney U test, and Spearman correlation test (p < 0.05).

Results

The mean number of thick collagen fibers was higher in periapical cysts, while that of thin fibers was higher in granulomas (p = 0.00). Cysts emitted orange-yellow to red birefringence, whereas periapical granulomas had predominantly green fibers (p = 0.00). The mean inflammatory cell density was comparable in all groups (p = 0.129). The number of total, degranulated, and granulated mast cells exhibited significant results (p = 0.00) in both groups. Thick cyst fibers showed significant inverse correlations with inflammation and degranulated mast cells (p = 0.041, 0.04 respectively).

Conclusions

Mast cells and inflammatory cells influenced the nature of collagen fiber formation and its birefringence. This finding may assist in the prediction of the nature, pathogenesis, and biological behavior of periapical lesions.

Langerhans Cells Correlate With Macrophages for Defense Mechanisms in the Atrophic Epithelium of Radicular Cysts

Langerhans cells (LCs) play important roles in cell-mediated immune reactions, as well as in the pathogenesis of periapical lesions. The aim of this study is to evaluate the role of LCs in the proliferative epithelium of radicular cysts (RCs) and the release of the proinflammatory cytokine tumor necrosis factor α (TNF-α) associated with epithelial thickness. Thirty cases of RCs and 30 cases of residual RCs were randomly selected. Morphologic analysis was performed to evaluate the association between the inflammatory infiltrate, cystic epithelial thickness and lesion size, in addition to immunohistochemical assessment of CD1a, CD68, and TNF-α. The highest macrophage percentages and TNF-α scores were found in RCs (P=0.038 and 0.017, respectively). The largest number of LCs was observed in RCs (P=0.021), especially those exhibiting atrophic epithelium (P=0.05). In addition, LCs were positively correlated with the number of macrophages in both RCs and residual RCs (P=0.033 and 0.002, respectively). In contrast to LCs, the largest number of macrophages was detected in cases with an intense inflammatory infiltrate (P=0.022). In addition, the highest TNF-α scores were associated with an intense inflammatory infiltrate (P=0.024) when analyzed in the capsule of RCs (P=0.017). In conclusion, LCs participate in defense mechanisms and were present in all cases evaluated. Along with macrophages, these cells release proinflammatory cytokines such as TNF-α, which is responsible for inducing the continued proliferation of cystic epithelium.