Selenium attenuates tolfenpyrad-induced immunotoxicity in the spleen and Peyer’s patches of albino rats

Abstract Background Tolfenpyrad (TPD) is a pyrazole insecticide that acts primarily by inhibiting mitochondrial respiratory chain complex I, potentially resulting in oxidative stress and cellular energy depletion. Its increasing agricultural use has raised concerns regarding possible immunotoxic effects in non-target organisms. Selenium (Se) is an essential trace element incorporated into antioxidant selenoproteins and contributes to redox homeostasis and immune function. This study evaluated the effects of TPD on the spleen and Peyer’s patches of female rats and investigated the potential protective effect of selenium co-administration. Methods Twenty female Sprague–Dawley rats, aged 6–8 weeks, were randomly allocated to four groups ( n = 5 per group): negative control, TPD-treated (50 mg/kg body weight), selenium-treated (5 mg/kg body weight), and combined TPD plus selenium treatment. Treatments were administered orally once daily for ten consecutive days. Body weight, spleen weight, hematological parameters, and histopathological changes in the spleen and Peyer’s patches were evaluated. Quantitative morphometric measurements of splenic white-pulp diameter and Peyer’s-patch dimensions were also performed. Results TPD exposure was associated with body weight loss, reduced spleen weight, and marked histopathological alterations in lymphoid tissues, including white pulp disorganization, lymphoid follicle atrophy, hemorrhage, and reduced lymphocyte density. Peyer’s patches exhibited reduced cellularity and structural degeneration. Most hematological parameters showed relatively limited changes during the 10-day exposure period. In comparison with TPD treatment alone, selenium co-administration was associated with partial preservation of splenic and intestinal lymphoid architecture and improvements in selected tissue and hematological outcomes. Morphometric analysis showed significantly smaller splenic white-pulp diameter and Peyer’s-patch height in the TPD group. The combined TPD plus selenium group exhibited significantly greater white-pulp diameter, Peyer’s-patch height, and Peyer’s-patch area than the TPD group. Conclusions Within this exploratory 10-day study, TPD exposure was associated with histopathological and morphometric alterations in the spleen and Peyer’s patches, whereas selenium co-administration was associated with partial preservation of lymphoid-tissue architecture. Because oxidative-stress biomarkers, mitochondrial function parameters, molecular endpoints, and immunohistochemical markers were not measured, the proposed mitochondrial and redox mechanisms remain biologically plausible interpretations rather than experimentally demonstrated mechanisms.