DNA Immunization with Na+-K+ATPase (Sseat-6) Induces Protective Immunity to Larval Strongyloides stercoralisin Mice

ABSTRACTStrongyloides stercoraliscauses chronic asymptomatic infections which can be maintained in the human host for many decades. Identification and treatment of S. stercoralis-infected individuals is required because immunosuppression can lead to fatal hyperinfection. In this study, human immunoglobulin G (IgG) that had previously been shown to transfer protective immunity to mice was used to identify potential protective antigens. Three antigens or genes from S. stercoralislarvae were identified as tropomyosin (Sstmy-1), Na+-K+ATPase (Sseat-6), and LEC-5 (Sslec-5). The genes were cloned into plasmids for DNA immunization, and mice were immunized intradermally with the three plasmids individually in combination with a plasmid containing murine granulocyte-macrophage colony-stimulating factor. Only Na+-K+ATPase induced a significant reduction in larval survival after DNA immunization. Immunization with a combination of all three plasmids, including Na+-K+ATPase, did not induce protective immunity. Serum from mice immunized with DNA encoding Na+-K+ATPase was transferred to naïve mice and resulted in partial protective immunity. Therefore, DNA immunization with Na+-K+ATPase induces protective immunity in mice, and it is the first identified vaccine candidate against infection with larval S. stercoralis.