Identification of infective larva (L3) proteins of Strongyloides stercoralis by immunoblot

Strongyloides stercoralis is prevalent in tropical and subtropical regions worldwide. This parasite is the only nematode with the ability to multiply in its host''s body via autoinfection transmission. Larvae detection in feces is difficult partly because of low egg production and also irregular larvae excretion in feces. Serologic tests (ELISA, IFA) are also diagnostic, however Strongyloides stercoralis antigens are not available as a diagnostic tool. In the present study, we analyzed filariform larva (L3) proteins of Strongyloides stercoralis by the immunoblot technique. Stool samples were examined by direct smear, formalin-ether and agar plate method to identify infected patients. Sera were also obtained and stored at -20°С. Infective larvae were then obtained by agar plate culture, which was incubated for 6-7days at 25ºC, then frozen at –70°С. Finally, larvae were suspended at a concentration level of 12000 in 250ml PBS, containing protease inhibitors and then were sonicated. Protein level was measured by Bradford method. Proteins of Strongyloides stercoralis filariform larvae were separated by SDS-PAGE, blotted onto nitrocellulose paper. Western blot analysis of these antigens was achieved using infected human sera (0.1, 0.01, 0.001 dilution) with strongyloidiasis, toxocariasis, hydatidosis, amebiasis and normal human serum as control. Four immunodominant proteins (23, 28, 30, 41 kDa) were recognized with strongyloidiasis sera in 0.1 diluted serum. None of the proteins reacted to normal human and amebiasis serum, but some showed reaction with serum of hydatidosis and toxocariasis. Having increased the level of serum dilution, only 41 kDa protein was recognized by strongyloidiasis sera. Other serums did not represent any reaction to the parasite’s proteins. Therefore, the 41 kDa protein presents as the most important immunodominant protein in this study. The identification of immunodominant proteins adapted to the physiological and genetic conditions of the host is an appropriate diagnostic approach, which could be associated with improved sensitivity and specificity of serologic tests.