The ultrastructure of the giant cell surrounding larvae of Thelazia spp. (Nematoda: Thelazioidea) in the face fly, Musca autumnalis De Geer

Abstract

The larval nematode, Thelazia spp., initiates a tissue response by the body-wall epidermal cells of its normal intermediate host, Musca autumnalis, resulting in the formation of giant cells. These giant cells differ in several ways from hemocytic capsules: they are larger, lack signs of necrosis, protect the parasite, and represent a true syncytium. Both, however, are considered to be the result of a defensive reaction by the host. Giant cells contain the following organelles which are absent from hemocytic capsules: hypertrophied nuclei, smooth-surfaced endoplasmic reticulum, and annulate lamellae. Further, unlike hemocytic capsules, giant cells lack cell junctions and cytolysosomes. Formation of giant cells is considered beneficial to both the host and the parasite.