Abstract
BackgroundSchistosomal parasites can establish parasitization in a human host for decades; evasion of host immunorecognition including surface masking by acquisition of host serum components is one of the strategies explored by the parasites. Parasite molecules anchored on the membrane are the main elements in the interaction. Sjc23, a member of the tetraspanin (TSP) family of Schistosoma japonicum, was previously found to be highly immunogenic and regarded as a vaccine candidate against schistosomiasis. However, studies indicated that immunization with Sjc23 generated rapid antibody responses which were less protective than that with other antigens. The biological function of this membrane-anchored molecule has not been defined after decades of vaccination studies.Methodology and Principal FindingsIn this study, we explored affinity pull-down and peptide competition assays to investigate the potential binding between Sjc23 molecule and human non-immune IgG. We determined that Sjc23 could bind human non-immune IgG and the binding was through the interaction of the large extra-cellular domain (LED) of Sjc23 (named Sjc23-LED) with the Fc domain of human IgG. Sjc23 had no affinity to other immunoglobulin types. Affinity precipitation (pull-down assay) in the presence of overlapping peptides further pinpointed to a 9-amino acid motif within Sjc23-LED that mediated the binding to human IgG.Conclusion and Significance S. japonicum parasites cloak themselves through interaction with human non-immune IgG, and a member of the tetraspanin family, Sjc23, mediated the acquisition of human IgG via the interaction of a motif of 9 amino acids with the Fc domain of the IgG molecule. The consequence of this interaction will likely benefit parasitism of S. japonicum by evasion of host immune recognition or immunoresponses. This is the first report that an epitope of schistosomal ligand and its immunoglobulin receptor are defined, which provides further evidence of immune evasion strategy adopted by S. japonicum.
Highlights
Schistosomiasis is one of the most serious parasitic diseases in morbidity and mortality, which infects at least 207 million people and a large number of animals in 76 countries,with an estimated 700 million people at risk (World health Organization, February 2010)
S. japonicum parasites cloak themselves through interaction with human non-immune IgG, and a member of the tetraspanin family, Sjc23, mediated the acquisition of human IgG via the interaction of a motif of 9 amino acids with the Fc domain of the IgG molecule
The consequence of this interaction will likely benefit parasitism of S. japonicum by evasion of host immune recognition or immunoresponses. This is the first report that an epitope of schistosomal ligand and its immunoglobulin receptor are defined, which provides further evidence of immune evasion strategy adopted by S. japonicum
Summary
Schistosomiasis is one of the most serious parasitic diseases in morbidity and mortality, which infects at least 207 million people and a large number of animals in 76 countries,with an estimated 700 million people at risk (World health Organization, February 2010). Vaccines based on the membrane components (or associated membrane proteins) have been extensively studied but with little success [4,5]. It has been well-known that schistosomal parasites evade host immune expulsion through surface masking, molecular mimicking, and active modulation on host immune responses [6]. The nonfilamentous paramyosin in association with parasite membrane of both S. mansoni and S. japonicum was the only molecule characterized as the receptor for un-specific binding of host (human and rodents) IgG and complement components, while the other parasite ligands that interact with host factors remain unidentified [7,8,9,10]. The biological function of this membraneanchored molecule has not been defined after decades of vaccination studies
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