Mast Cell Characterization and Density in Normal and Abnormally Invasive Placental Tissue Using Five Histochemical Stains

Mast cells (MCs) are multifunctional immune cells implicated in tissue remodeling and immune regulation. Yet, their densities and distribution in human placental tissues, particularly in cases of abnormal placental invasion such as placenta accreta spectrum (PAS), remain underexplored. While immunohistochemistry is considered the gold standard for MCs identification, it is resource-intensive, requiring specialized skills, making histochemical staining a practical alternative. Limited studies have provided conflicting results on the most effective histochemical stains for identifying MCs in human placental tissues. This study aimed to evaluate mast cell density and characterize their histochemical staining properties in placental tissues from control and experimental groups. The control group comprised five normal full-term placentas obtained from vaginal deliveries, while the experimental group included five placentas from cases of placenta accreta spectrum (PAS) delivered by abdominal hysterectomy. Additionally, the study sought to identify the most effective histochemical stain for mast cell identification and characterization Five histochemical stains; Toluidine Blue, Periodic Acid-Schiff, Giemsa, Hematoxylin & Eosin (H&E), and Alcian Blue with Safranin O were used to stain sections from each placental sample of the control and the experimental groups. MCs were counted in 10 fields at ×400 magnification for each section, and their densities were compared between the control and the PAS cases for all stains used. Statistical significance was set at p = 0.05. Toluidine Blue enabled the highest mast cell counts, outperforming other stains in identifying and characterizing mast cells. Morphologically, three types of mast cells were recognized according to their granular content. Mast cell densities were significantly higher in placenta accreta cases compared to the control, suggesting a potential role for MCs in the pathogenesis of PAS. In conclusion, this study highlights the value of histochemical staining—particularly Toluidine Blue—in reliably identifying mast cells within placental tissue. The findings suggest a possible involvement of mast cells in the pathogenesis of placenta accreta, warranting further research into their underlying mechanisms and their potential utility as diagnostic markers or therapeutic targets KEYWORDS: Mast cells, Placenta Accreta Spectrum, Histochemical staining, Toluidine Blue.