The aim of the present work was to evaluate the number of apoptotic eosinophils in the livers
of sheep experimentally infected with Fasciola hepatica during the migratory and biliary
stages of infection. Four groups (n = 5) of sheep were used; groups 1-3 were orally infected
with 200 metacercariae (mc) and sacrificed at 8 and 28 days post-infection (dpi), and 17
weeks post-infection (wpi), respectively. Group 4 was used as an uninfected control.
Apoptosis was detected using immunohistochemistry with a polyclonal antibody against antiactive
caspase-3, and transmission electron microscopy (TEM). Eosinophils were identified
using the Hansel stain in serial sections for caspase-3, and by ultrastructural features using
TEM. At 8 and 28 dpi, numerous caspase-3+ eosinophils were mainly found at the periphery
of acute hepatic necrotic foci. The percentage of caspase -3+ apoptotic eosinophils in the
periphery of necrotic foci was high (46.1 to 53.9) at 8 and 28 dpi, respectively, and decreased
in granulomas found at 28 dpi (6%). Transmission electron microscopy confirmed the
presence of apoptotic eosinophils in hepatic lesions at 8 and 28 dpi. At 17 wpi, apoptotic
eosinophils were detected in the infiltrate surrounding some enlarged bile ducts containing
adult flukes. This is the first report of apoptosis induced by F. hepatica in sheep and the first
study reporting apoptosis in eosinophils in hepatic inflammatory infiltrates in vivo. The high
number of apoptotic eosinophils in acute necrotic tracts during the migratory and biliary
stages of infection suggests that eosinophil apoptosis may play a role in F. hepatica survival
during different stages of infection.