Identification of a linear B-cell epitope on the Schistosoma japonicum saposin protein, SjSAP4: Potential as a component of a multi-epitope diagnostic assay

Yi Mu; Catherine A Gordon; Remigio M Olveda; Allen G Ross; David U Olveda; Jessica M Marsh; Donald P McManus; Pengfei Cai

doi:10.1371/journal.pntd.0010619

Identification of a linear B-cell epitope on the Schistosoma japonicum saposin protein, SjSAP4: Potential as a component of a multi-epitope diagnostic assay

PLoS Negl Trop Dis. 2022 Jul 11;16(7):e0010619. doi: 10.1371/journal.pntd.0010619. eCollection 2022 Jul.

Authors

Yi Mu¹, Catherine A Gordon¹, Remigio M Olveda², Allen G Ross³, David U Olveda⁴, Jessica M Marsh⁵, Donald P McManus¹, Pengfei Cai¹

Affiliations

¹ Molecular Parasitology Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Australia.
² Research Institute for Tropical Medicine, Department of Health, Manila, Philippines.
³ Research Institute for Rural Health, Charles Sturt University, Orange, Australia.
⁴ Department of Pathology, JONELTA Foundation School of Medicine, University of Perpetual Help Rizal, Manila, Philippines.
⁵ The School of Biomedical Sciences, Queensland University of Technology, Brisbane, Australia.

Abstract

Background: Schistosoma japonicum is one of three major species of blood flukes causing schistosomiasis, a disease, which continues to be a major public health issue in the Philippines. SjSAP4, a member of a multigene family of saposin-like proteins, is a recognized immunodiagnostic biomarker for schistosomiasis japonica. This study aimed to identify linear B-cell epitopes on SjSAP4 and to validate their potential as components of a multi-epitope assay for the serological diagnosis of schistosomiasis japonica.

Methodology: SjSAP4-derived peptides were expressed as GST-peptide-fused proteins and these were Western blot probed with human serum samples from S. japonicum Kato-Katz (KK)-positive individuals and uninfected controls. A core epitope was further identified by Western blotting through probing a series of truncated peptides with the schistosomiasis patient sera. The diagnostic performance of the core epitope-containing peptides and the full-length SjSAP4 was evaluated by enzyme-linked immunosorbent assay (ELISA) using a panel of sera collected from subjects resident in a schistosomiasis-endemic area of the Philippines.

Main findings: As a result of the peptide mapping, one peptide (P15) was found to be highly immunogenic in the KK-positive individuals. We subsequently showed that -S163QCSLVGDIFVDKYLD178- is a core B-cell epitope of P15. Subsequent ELISAs incorporating SjSAP4, SjSAP4-Peptide and SjSP-13V2-Peptide showed a sensitivity of 94.0%, 46.0% and 74.0%, respectively, and a specificity of 97.1%, 100% and 100%, respectively. Notably, complementary recognition of the B-cell epitopes (SjSAP4-Peptide and SjSP-13V2-Peptide) was observed in a subset of the KK-positive individuals. A dual epitope-ELISA (SjSAP4-Peptide + SjSP-13V2-Peptide-ELISA) showed a diagnostic sensitivity of 84.0% and a specificity of 100%.

Conclusions/significance: In this study, -S163QCSLVGDIFVDKYLD178- was identified as a dominant linear B-cell epitope on SjSAP4. This peptide and the complementary recognition of other B-cell epitopes using sera from different KK-positive individuals can provide the basis of developing a multi-epitope assay for the serological diagnosis of schistosomiasis.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Antigens, Helminth
Enzyme-Linked Immunosorbent Assay
Epitopes, B-Lymphocyte
Humans
Peptides
Saposins
Schistosoma japonicum*
Schistosomiasis japonica*
Sensitivity and Specificity

Substances

Antigens, Helminth
Epitopes, B-Lymphocyte
Peptides
Saposins

Grants and funding

This work was funded by the National Health and Medical Research Council (NHMRC) of Australia (ID: APP1160046, APP2008433, APP1098244, APP1102926 and APP1037304). DPM is a NHMRC Leadership Fellow and Senior Scientist at QIMRB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.