Recombinant micro-exon gene 3 (MEG-3) antigens from Schistosoma mansoni failed to induce protection against infection but show potential for serological diagnosis.

Sequence databases on Schistosoma mansoni have revealed micro-exon gene (MEGs) families. Many of these genes are highly expressed in parasite life cycle stages associated with the mammalian host infection and appear to be involved in immune evasion by schistosomes. So, we believe that MEG-coding proteins would make potential candidates for vaccine development or diagnosis for schistosomiasis. Here, we study MEG-3.2 and MEG-3.4, members of the MEG-3 family. Recombinant (r) proteins were produced and formulated with Freund's adjuvant for vaccination of mice. Immunization with recombinant MEG-3.2 or MEG-3.4 formulation generated high levels of IgG1 antibodies. Additionally, vaccination also induced a mixed Th1/Th2/Th17-type of response, since IFN-γ, IL-5 and IL-17 cytokines were detected in the supernatant of spleen cell cultures; however it failed to induce reduction in parasitic worm burden. Finally, the recombinant proteins were evaluated in a serological assay using human samples. Schistosome-infected individuals showed higher levels of both IgG and IgM against rMEG-3.2 compared to non-infected individuals, while only IgM anti-rMEG-3.4 antibodies were elevated in infected patients. Therefore, between both studied molecules, MEG-3.2 protein is the antigen that shows potential to compose a serological diagnosis test for schistosomiasis.