Antigenic relationships between the surface-exposed, secreted and somatic materials of the nematode parasites Ascaris lumbricoides, Ascaris suum, and Toxocara canis.

The cosmopolitan nematode parasites Ascaris lumbricoides, Ascaris suum, and Toxocara canis are closely related phylogenetically, and are all pathogenic to man. In the case of the latter, the antigens released by the tissue-invasive parasitic larvae in vitro ('excretory/secretory' or 'ES' antigens) are routinely used for serodiagnostic purposes. Here we have found, using radioimmunoprecipitation with defined rabbit antiserum, and SDS-PAGE, that there is a significant antigenic similarity between the secreted and somatic antigens of the three nematodes, and have characterized cross-reactive components. Among these is a 14 kD internal protein which has a homologue in all three parasites. This molecule is the subject of an IgG antibody response in Ascaris infection, but there is no measurable response to it in toxocariasis. Lastly, using quantitative immunofluorescence, the antigens exposed on the surface of intact, living, larvae were found to be cross-reactive or specific depending on the developmental stage of the parasites. This means that the surface of tissue-invasive Ascaris larvae bears stage-specific epitopes.