Immunological and ultrastructural aspects of the cell-mediated killing of Dirofilaria immitis microfilariae.

Abstract

Neutrophils in the presence of serum from dogs with occult Dirofilaria immitis infections were shown to be cytotoxic to D. immitis microfilariae recovered from the blood of microfilaraemic dogs. This cytotoxicity was correlated with the presence of IgM and IgG antibodies on the cuticular surface of microfilariae incubated in the sera from occult dogs. Such antibodies were not observed on the surface of microfilariae incubated in sera from microfilaraemic or normal dogs. The neutrophil attack was directed at the cuticular crypts, at which sites the worms appeared to be structurally most vulnerable because of the absence of the outer layer of the cuticle. The IgM antibodies were shown to be bound preferentially to these sites. Our data suggested that the neutrophil-mediated toxicity involved both hydrogen peroxide release and degranulation.