Characterization of three types of Schistosoma mansoni soluble egg antigen and determination of their immunodiagnostic potential by western blot immunoassay.

On the search of highly sensitive and specific antigenic components for use in serological tests, the serologic activities of the various protein fractions of three types of Schistosoma mansoni soluble egg antigen (SEA) were compared in an immunoblot analysis for their ability to detect schistosomiasis mansoni infections . Three types of soluble egg antigen (SEA) were prepared from three suspensions of Schistosoma mansoni eggs; namely living SEA (L-SEA), dead SEA (D-SEA) and mixed SEA (M-SEA). The three antigens were resolved by sodium dodecyl sulphate polyacrylamide gel electrophoresis. A total of 80 Egyptian individuals were enrolled in the present study. After being screened by clinical examination, urine and stool analysis, sigmoidoscopy rectal snip examination, abdominal ultrasonography and indirect haemagglutination test (IHAT), the study population were grouped into an active intestinal schistosomiasis group (group I, n=20), a schistosomiasis seropositive group by IHA test (group II, n=20), a parasite control group including 10 patients with hydatidosis & 10 patients with fascioliasis (group III, n = 20) and a normal control group (group IV, n=20). Sera of all subjects were studied by immunoblotting for the presence of IgG antibodies against the various protein fractions of the three prepared types of SEA. Several protein bands from the 3 types of SEA reacted with the schistosomiasis patients' sera in a heterogenous manner. However, a 31-32 kilo daltons (kDa) protein fraction of L-SEA reacted with 80% (16/20) of group I sera, 40% (8/20) of group II sera, one hydatidosis serum, but no reaction occurred with normal sera. Also, in the active intestinal schistosomiasis group, the 31-32 kDa fraction of L-SEA was more recognized by patients with early active intestinal schistosomiasis without organomegaly (100%, 12/12) than in those with organomegaly (50%, 4/8) (P < 0.05). On the other hand, a 80-82 kDa band of M-SEA was recognized by 70% (14/20) of group 1, 30% (6/20) of group II & sera from 3 hydatidosis and 2 fascioliasis cases, but not by normal human sera. So, it can be concluded that the 31-32 kDa protein fraction of L-SEA is highly immunogenic, with the least cross reaction with other parasitic infections, and may be a useful serologic marker for diagnosing and differentiating between early and chronic schistosomiasis mansoni infection.