Coccidiosis in chickens is a parasitic disease caused by Eimeria species, resulting in significant economic losses to the poultry industry. Among these species, Eimeria tenella is considered the most virulent pathogen, with its infection strongly associated with the apoptotic response of host cells. Eimeria tenella modulates host cell apoptosis in a stage-specific manner, suppressing apoptosis in the early phase to promote its intracellular development and triggering apoptosis in later stages to facilitate parasite egress and disease progression. This study established an in vitro infection model using 60 fifteen-day-old chick embryo cecal epithelial cells and infecting the cells with Eimeria tenella sporozoites at a 1:1 ratio of host cells to sporozoites. The aim was to examine the relationship between parasitic infection and the apoptotic response of host cells in the chick embryo cecal epithelial cells infected with E. tenella. The roles of the mitochondrial permeability transition pore (MPTP) and cytochrome c in intrinsic apoptosis were examined through the application of cyclosporine A (CsA), N, N, N’, N’-tetramethyl-1,4-phenylenediamine (TMPD), and ascorbate (Asc). TUNEL staining, ELISA, and flow cytometry were performed to evaluate apoptotic rates. CsA, TMPD, and Asc significantly (p < 0.01) decreased cytochrome c release, caspase-9 activation, and apoptotic rates from 24 to 120 h post-E. tenella infection. These findings highlight the significance of cytochrome c-mediated, mitochondria-dependent apoptotic pathways in parasitized chick embryo cecal epithelial cells.

Coccidiosis due to Eimeria tenella remains a major constraint on the poultry industry. Previous studies have revealed that E. tenella infection triggers apoptosis in host cells. The mitochondrial permeability transition pore (MPTP) plays a pivotal role in the apoptosis and necrosis observed in infected host cells. However, the effect of MPTP opening on mitochondrial apoptotic factors remains unclear. To elucidate the dynamic changes in apoptotic signals during MPTP-mediated apoptosis in host cells infected with E. tenella, we established a chicken embryo caecal epithelial cell infection model. Cyclosporin A (CsA) was used to inhibit the MPTP. The infection rate was assessed by Hematoxylin and eosin (H&E) staining, whereas MPTP opening and the abundances of the mitochondrial apoptotic factors Smac, Endo G, and AIF were determined by flow cytometry and ELISA, respectively. The results revealed that both the degree of MPTP opening was markedly reduced in the E. tenella+CsA group compared to the E. tenella group (p < 0.05). Between 24 and 120 h post-infection (hpi), the cytoplasmic levels of Smac, Endo G, and AIF were significantly elevated in the E. tenella group compared with the control group (p < 0.05), while their mitochondrial levels were markedly decreased (p < 0.05). In contrast, mitochondrial expression of these factors was restored in the E. tenella+CsA group (p < 0.05), accompanied by a reduction in their cytoplasmic abundance (p < 0.05). These findings indicate that E. tenella promotes MPTP-dependent release of mitochondrial pro-apoptotic factors into the cytosol during the mid-to-late stages of infection, whereas pharmacological inhibition of the MPTP limits this redistribution.