Schistosomiasis is a parasitic disease caused by parasitic flatworms of the genus Schistosoma that live in the mesenteric veins of definitive hosts (Zhong et al., 2022). The disease is mainly distributed in subtropical and tropical areas of 78 countries and regions, with approximately 800 million people at risk of infection and 241.3 million people requiring preventive chemotherapy (Xu et al., 2022). S. japonicum is one of the three major species of schistosome blood flukes causing the disease of schistosomiasis in humans in Asian countries such as China, the Philippines, and Indonesia (Mu et al., 2022). adult S. japonicum lay a large number of eggs, leading to significant pathological reactions of final hosts, which can be fatal to humans and animals (Gryseels et al., 2006; Tucker et al., 2013). Detection of Schistosoma eggs in feces is considered to be the gold standard for diagnosis of the disease (Katz et al., 1972), but this method suffer from some limitations such as relatively low sensitivity, increased time-consumption, skilled personnel being required for operation and lack of onsite applicability (Hamilton et al., 1998; Ullah et al., 2020). Consequently, it is necessary to develop alternative methods for schistosomiasis diagnosis.

Extracellular vehicles (EVs) secreted from S. japonicum could be ideal biomarkers for diagnosing pathogen infection (Zhu et al., 2016). In our previous study, we evaluated the potential of SjEV proteins as biomarkers for diagnosing schistosomiasis by ELISA, suggesting that S. japonicum EV proteins could serve as potential biomarkers for developing diagnostic tools for schistosomiasis (Chen et al., 2020; Wang et al., 2018). ELISA is a commonly used serological method for S. japonicum diagnosis, that requires a relatively large amount of recombinant antigen, mostly recombinant proteins expressed in prokaryotes (Cai et al., 2017). In addition, the structure of these recombinant proteins may not be identical to that of natural proteins, which can affect the specificity and sensitivity of the assay. In contrast, recombinant proteins expressed in eukaryotic organisms may have similar structures that are closer to organisms. The luciferase immunoprecipitation systems (LIPS) assay is a liquid phase immunoassay allowing high-throughput serological screening of antigen-specific antibodies (Burbelo et al., 2010; Burbelo et al., 2009). The antigen-antibody specific complex obtained through pre-incubation, captured using protein A/G beads and then the luciferase activity is determined (Burbelo et al., 2012; Donelan et al., 2013). In addition, the usage of luciferase as a reporter offers significant sensitivity and also help to solve the problem of low expression of exogenous proteins in eukaryotic cells, eliminating the need for protein extraction and purification processes (Phonbuppha et al., 2023). Moreover, the antigen preparation method is relatively simple as compared to ELISA and immunofluorescence methods, the detection method is faster and more convenient (Burbelo et al., 2007). Currently, LIPS has been applied to detect pathogen specific antibodies for certain pathogens (Burbelo et al., 2008; Ding et al., 2022).

In the present study, based on our previously identified SjEV protein, we selected a saposin-like protein (SjSLP) as a diagnostic antigen to establish a LIPS method. As compared with the indirect ELISA method derived from same antigen purified from prokaryotic cells, the LIPS showed higher sensitivity. Upon the comparison of diagnostic potential of the SjSLP with a well investigated antigen, Sj23, the results suggested that the LIPS combined with SjSLP protein can serve as alternative method for detecting S. japonicum infection.