Schistosoma mansoni: Immunodiagnosis is improved by sodium metaperiodate which reduces cross-reactivity due to glycosylated epitopes of soluble egg antigen

ELISA with soluble egg antigen (SEA) from Schistosoma mansoni is widely use d in the diagnosis of schistosomiasis, but cross-reactivity with other inte stinal helminths, overestimating the true prevalence, represents a great li mitation. The role of glycoproteins of SEA in cross-reactions was investiga ted. SEA was oxidized with sodium metaperiodate (SMP) in ELISA and immunobl ot. One hundred schistosomiasis-negative individuals sera were submitted to SMP-ELISA improving the specificity from 73% without SMP treatment to 97% with SMP. On the other hand, 94 S. mansoni-positive sera were evaluated sho wing that 99% were positive in ELISA either with or without SMP treatment, indicating the maintenance of high sensitivity under SMP treatment. By immu noblot, 24 sera from persons with schistosomiasis and 10 sera from schistos omiasis-free persons were assayed under reducing and nonreducing conditions with or without SMP, looking for specific infection markers and crossreact ivity markers. Reactivity from positive sera showed that specific molecules were mainly low-molecular-mass antigens and seem to have predominant prote ic epitopes. The unspecific molecules reacting with some schistosomiasis-ne gative individuals harboring other intestinal parasites (false-positive ser a) were mostly larger than 60 kDa and seemed to be basically glycosylated. Glycosylated epitopes have an important role in cross-reaction and SMP can successfully be used to reduce the false reactivity of SEA with no decrease in sensitivity, especially in ELISA as an immunodiagnostic screening surve illance method, which is useful in areas of low schistosomiasis transmissio n. (C) 2000 Academic Press.