Refractile bodies (RBs) in human primordial oocytes may represent a lysosomal mechanism of cellular waste management independent of hormonal stimulation or age. This observational study investigated the ultrastructural features and molecular characteristics of refractile bodies (RBs) in human primordial oocytes, focusing on the involvement of lysosomes, autophagy, and mitochondria. Ovarian tissues were obtained from 34 individuals undergoing oophorectomy as part of female-to-male gender-affirming surgery, with no clinical interventions applied. Using fluorescence microscopy, immunocytochemistry, and transmission electron microscopy (TEM), we found large RBs (>5 μm) in all individuals, with no correlation to age. RBs exhibited strong LysoTracker fluorescence, indicating acidic content. LC3, but not RAB7, colocalized with RBs, suggesting incomplete autophagic processing. TEM revealed lysosomal vesicles, mitochondrial remnants, and lipid-rich structures within RBs, some partially enclosed by isolation membranes. These features support a model in which RBs transition from passive lipid accumulation to autophagy-driven remodeling in a size-dependent manner. RBs displayed lipofuscin-like characteristics and are likely formed through lysosomal and mitophagic pathways. Their formation appears to involve both canonical and non-canonical autophagic mechanisms, independent of age or hormonal stimulation. A limitation of this study is its observational nature without functional validation.
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