M2 Phenotype Macrophages Colocalize with Schwann Cells in Human Dental Pulp.

Macrophages are immune cells with high plasticity that perform many functions related to tissue injury and repair. They are generally categorized as 2 functional phenotypes: M1 (proinflammatory) and M2 (anti-inflammatory and prohealing). To investigate the role of macrophages in human dental pulp, we examined the localization and distributional alterations of macrophages in healthy dental pulp as well as during the reparative process of pulp capping with mineral trioxide aggregate (MTA) and in cariously inflamed pulp of adult human teeth. We also quantified the populations of M1/M2 macrophages in healthy dental pulp by flow cytometric analysis. CD68+CD86+ cells (M1 phenotype) and CD68+CD163+ cells (M2 phenotype) were 2.11% ± 0.50% and 44.99% ± 2.22%, respectively, of 2.96% ± 0.41% CD68+ cells (pan-macrophages) in whole healthy dental pulp. Interestingly, M2 phenotype macrophages were associated with Schwann cells in healthy pulp, during mineralized bridge formation, and in pulp with carious infections in vivo. Furthermore, the M2 macrophages associated with Schwann cells expressed brain-derived neurotrophic factor (BDNF) under all in vivo conditions. Moreover, we found that plasma cells expressed BDNF. Coculture of Schwann cells isolated from human dental pulp and human monocytic cell line THP-1 showed that Schwann cells induced M2 phenotypic polarization of THP-1 cell-derived macrophages. The THP-1 macrophages that maintained contact with Schwann cells were stimulated, leading to elongation of their cell shape and expression of M2 phenotype marker CD163 in cocultures. In summary, we revealed the spatiotemporal localization of macrophages and potent induction of the M2 phenotype by Schwann cells in human dental pulp. M2 macrophages protect neural elements, whereas M1 cells promote neuronal destruction. Therefore, suppressing the neurodestructive M1 phenotype and maintaining the neuroprotective M2 phenotype of macrophages by Schwann cells may be critical for development of effective treatment strategies to maintain the viability of highly innervated dental pulp.

Detection of bone marrow-derived fibrocytes in human dental pulp repair.

AIM: To explore the expression profile of CD45+/pro-collagen I+ fibrocytes in intact dental pulps as well as during wound healing in adult dental pulp tissue. METHODOLOGY: A total of 16 healthy permanent teeth were obtained from young patients (18 to 25 years) undergoing orthodontic treatment. Routine pulp capping with mineral trioxide aggregate (MTA) was performed under local anaesthesia to induce a mineralized barrier at the exposed surface. Teeth were extracted from patients after 7, 14 and 35 days. Sections of the extracted teeth were prepared and stained for various markers using indirect immunofluorescence. Fibrocytes were counted, and the data were statistically evaluated using the Dunnett test. RESULTS: In uninflammed pulp tissue, a pro-collagen I-positive reaction was detected in odontoblasts, as well as in perivascular cells. Most of the CD45-positive cells were negative for pro-collagen I in normal pulp tissue, whereas CD45+/pro-collagen I+ fibrocytes were detected 7 days after injury. At day 14, fibrocytes were recognized under the fibrous matrix in contact with MTA and had infiltrated into regions of new capillary formation, where the fibrocytes were positively stained for vascular endothelial growth factor. By 35 days, fibrocytes were few, coincident with the formation of dentine bridges. The number of fibrocytes peaked 7 days post-injury and decreased at 14 days. CONCLUSIONS: The presence of fibrocytes in human pulp wound healing was observed. The spatiotemporal distribution of fibrocytes suggests that fibrocytes are involved in the early stages of pulp wound healing, specifically by contributing to new blood vessel formation.

Bioactivity and biomineralization ability of calcium silicate-based pulp-capping materials after subcutaneous implantation.

AIM: To evaluate the abilities of three calcium silicate-based pulp-capping materials (ProRoot MTA, TheraCal LC and a prototype tricalcium silicate cement) to produce apatite-like precipitates after being subcutaneously implanted into rats. METHODOLOGY: Polytetrafluoroethylene tubes containing each material were subcutaneously implanted into the backs of Wistar rats. At 7, 14 and 28 days post-implantation, the implants were removed together with the surrounding connective tissue, and fixed in 2.5% glutaraldehyde in cacodylate buffer. The chemical compositions of the surface precipitates formed on the implants were analysed with scanning electron microscopy-electron probe microanalysis (SEM-EPMA). The distributions of calcium (Ca) and phosphorus (P) at the material-tissue interface were also analysed with SEM-EPMA. Comparisons of the thicknesses of the Ca- and P-rich areas were performed using the Friedman test followed by Scheffe's test at a significant level of 5%. RESULTS: All three materials produced apatite-like surface precipitates containing Ca and P. For each material, elemental mapping detected a region of connective tissue in which the concentrations of Ca and P were higher than those in the surrounding connective tissue. The thickness of this Ca- and P-rich region exhibited the following pattern: ProRoot MTA > prototype tricalcium silicate cement ≥ TheraCal LC. ProRoot MTA had a significantly thicker layer of Ca and P than the other materials at all time-points (P < 0.05), and a significant difference was detected between the prototype cement and TheraCal LC at 28 days (P < 0.05). CONCLUSION: After being subcutaneously implanted, all of the materials produced Ca- and P-containing surface precipitates and a Ca- and P-rich layer within the surrounding tissue. The thickness of the Ca- and P-rich layer of ProRoot MTA was significantly thicker than that of the other materials.