Stereological analysis of spleen alterations in streptozotocin-nicotinamide-induced diabetic rats

Studies have indicated that spleen and white pulp atrophy develops within 5 weeks following hyperglycemia onset in streptozotocin-induced diabetic rats. This study aimed to delineate the histopathological alterations in the spleen across two stages of diabetes progression using design-based stereology. Twenty-six rats were categorized into four groups based on condition (normal control [NC] or diabetic model [DM]) and observation period post-induction (5 or 10 weeks): NC5, DM5, NC10, and DM10. Diabetes was induced using streptozotocin-nicotinamide combination. Histological evaluations were performed using standard staining techniques, whereas spleen compartment volumes were quantitatively assessed through point-counting methods on histological sections. Additionally, immunohistochemistry (IHC) and flow cytometry analyses were utilized to determine the distribution and percentages of T and B lymphocytes. Compared to its NC5 control, the DM5 group exhibited inflammatory responses, including polymorphonuclear leukocyte infiltration, but no significant atrophy. DM5 showed a significantly elevated IHC score for T lymphocytes (p < 0.01) and a higher percentage of CXCR5 + B lymphocytes (p < 0.05) compared to NC5, suggesting an active adaptive immune response. In contrast to the NC10 group, the DM10 group displayed significant spleen atrophy (p = 0.005), with marked reductions in total white pulp volume (p = 0.015) and marginal zone volume (p = 0.008). Furthermore, compared to NC10, DM10 exhibited an increased connective tissue volume fraction (p < 0.001). Across all groups, spleen atrophy was directly correlated with reductions in body weight. These findings underscore an initial inflammatory phase characterized by immune cell recruitment in the spleen during early diabetes, subsequently evolving into significant atrophy, reduced white pulp and marginal zone volumes, and an increased connective tissue volume fraction in advanced stages of the disease, all proportional to body weight loss.