The process of IIL invasion into the intestinal epithelium in vitro. AT. spiralis IIL were shown to invade the epithelial cell monolayer. Larvae penetrated IEC cells and migrated through them, leaving behind trails of dead cells and damaging the IEC monolayer. B Non-invaded larvae on the IEC monolayer. Nematodes that stayed coiled on the surface of the IEC monolayer or suspended in the medium were counted as non-invaded larvae. The IEC monolayer was intact. C Non-invaded larvae on the C2C12 cell monolayer. The larvae on the C2C12 monolayer were coiled. The C2C12 cell monolayer was not damaged. Scale bars: 100 μm.