Discussion

The present study evaluated the morphological, immunohistochemical, and ultrastructural characteristics of human fetal testicular tissue during different gestational periods. Progressive changes in testicular architecture, Leydig cell morphology, and cellular proliferative activity were observed with advancing gestational age. Human fetal testicular development involves coordinated differentiation of Sertoli cells, germ cells, and Leydig cells, with dynamic changes in hormonal activity and tissue organization during gestation [8].

Fetal Leydig cells play a critical role in male sexual differentiation through testosterone production, which regulates the development of the internal and external male reproductive system. In the present study, Leydig cells were prominently distributed within the interstitial compartment during early gestation and demonstrated strong cytoplasmic immunoreactivity, suggesting increased functional activity during this developmental phase. Similar observations have been reported in human fetal testes, where Leydig cell differentiation and steroidogenic activity are prominent during early fetal life, followed by progressive maturation of the interstitial compartment [9,10].

The reduction in Leydig cell immunoreactivity observed during later gestational periods in the present study may represent a physiological developmental transition rather than degenerative change. With advancing gestational age, seminiferous cords become progressively organized and occupy a larger proportion of the testicular parenchyma, resulting in relative reduction of interstitial cellularity. Previous studies have demonstrated progressive Sertoli cell differentiation and seminiferous cord maturation during fetal development [11].

Ki-67 immunohistochemistry was performed to evaluate proliferative activity in developing fetal testicular tissue. Strong immunoreactivity was observed in fetal epididymal epithelial cells and developing seminiferous structures, indicating active cellular proliferation during organ maturation. Ki-67 is a widely accepted marker of cellular proliferation and reflects active progression through the cell cycle [12]. The observed Ki-67 expression supports ongoing cellular expansion and differentiation during fetal testicular development.

Ultrastructural evaluation by SEM and TEM demonstrated preserved testicular organization without significant degenerative changes. Developing seminiferous cords and interstitial components showed maintained cellular integrity with progressive maturation of cellular components. Previous ultrastructural studies have described similar developmental changes in fetal human testes, including maturation of Leydig cells, Sertoli cells, and germ cells with characteristic alterations in cellular morphology and organelle distribution [12].

Although the present study was not designed to investigate toxic injury, previous studies have described cytoplasmic vacuolization of Sertoli cells as a morphological alteration associated with cellular stress and altered Sertoli cell function under experimental conditions [13,14]. Our observations provide a broader context for interpreting similar histological changes without implying a comparable pathogenic mechanism in the fetal testes examined in the present study.

The close association of Leydig cells with the vascular compartment may increase their susceptibility to circulating toxicants and endocrine-disrupting agents. Multivacuolated Leydig cells have been considered a morphological indicator of cellular stress or involution [9]. Alterations in peritubular myoid cells and extracellular matrix components may influence seminiferous tubular function. Increased collagen deposition and basement membrane thickening have been associated with disruption of seminiferous architecture and impaired spermatogenesis [15].

However, in contrast to these pathological observations, the fetal testicular tissue examined in the present study showed preserved architecture and absence of significant degenerative ultrastructural alterations. The findings suggest normal developmental progression rather than cellular injury. Understanding normal fetal testicular morphology is essential for distinguishing physiological maturation from developmental disorders such as cryptorchidism, testicular dysgenesis syndrome, and testicular tumors [16,17].

The present study provides detailed morphological and ultrastructural information regarding fetal testicular development in an Eastern Indian population. Such baseline information may contribute to future investigations related to reproductive biology and fertility preservation. Human fetal testicular tissue has been explored as an experimental model because of its developmental plasticity and vascular characteristics that may support maturation of germ cells after transplantation [18,19].

Limitations of the study

The present study has certain limitations. The sample size was limited because of restricted availability of ethically obtained human fetal testicular tissue. Therefore, larger studies involving a greater number of samples across different gestational periods are required to validate these findings. The study was primarily based on morphological, immunohistochemical, and ultrastructural evaluation; therefore, functional parameters such as fetal testosterone concentration, molecular markers of differentiation, and gene expression analysis could not be assessed. Additionally, quantitative stereological analysis of individual testicular cell populations was not performed. Despite these limitations, the present study provides important baseline information regarding normal human fetal testicular development.