Antigens from the surface and excretions/secretions of the filariform larva of Strongyloides stercoralis

The surface and excretory/secretory (ES) antigens of the infective, filariform larva (L3) of Strongyloides stercoralis were identified. These studies provide a basis for the purification of these proteins as diagnostic allergens for human strongyloidiasis. The M r values of the surface and ES molecules were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, fluorography, or silver staining following the recovery of these molecules after the radiolabelling of living parasites. At least 10 surface proteins were radioiodinated extrinsically using chloroglycoluril as the catalyst for iodination, and then extracted with detergents and/or β-mercaptoethanol. Several surface molecules of the L3 were immunogenic in humans, as determined by immunoprecipitation with sera (IHS) from infected patients. About 30 proteins were present in the ES preparation. Many ES antigens were labelled biosynthetically during the culture of larvae in media supplemented with either [ 35S]methionine or [ 14C]glucose. Furthermore, several of the surface proteins of the L3 were found with the ES antigens recoverable by culturing larvae in vitro. About 10 of the ES proteins were immunogenic as determined by immunoaffinity chromatography using IHS; and two of these antigens with M r 50 000 and 90 000 incorporated [ 35S]methionine during culture of larvae. Moreover, some ES proteins were allergenic when tested in an in vitro assay of histamine release from basophils from infected humans or monkeys. The isotype of the homocytophilic antibodies involved in this immediate hypersensitivity assay, which is the basis of a diagnostic skin test for human strongyloidiasis, appears to be IgE.