Human antibody response to thioredoxin peroxidase-1 and tandem repeat proteins as immunodiagnostic antigen candidates for Schistosoma japonicum infection

Abstract

Schistosomiasis continues to be a public health problem in many tropical and subtropical countries. Improving the diagnostic tools for surveillance and monitoring in areas that have reached elimination level will help hasten the possible elimination of this disease. This study therefore aims to develop enzyme-linked immunosorbent assay through the use of recombinant proteins such as thioredoxin peroxidase-1 (SjTPx-1) and four tandem repeat proteins (Sj1TR, Sj2TR, Sj4TR, and Sj7TR). Cutoff values were calculated using 38 serum samples from healthy Japanese volunteers. Sera from 35 schistosomiasis-confirmed patients, four cured from the disease by chemotherapy, and 15 endemic negative controls were used to assess these antigens. SjTPx-1 and Sj7TR both had 85.71% sensitivity. Furthermore, these antigens were also tested against human sera positive for other parasitic infections and showed no or very minimal cross-reaction. These results suggest the potential defined antigens for development of an accurate diagnostic test for schistosomiasis.

Figure 1.

Gel electrophoresis and polyacrylamide gel electrophoresis (SDS-PAGE) of the recombinant antigens. (A and B) The recombinant plasmids were identified by polymerase chain reaction (PCR) and enzyme digestion. (A) Lane 1: TPx-1 from the Schistosoma japonicum adult worm cDNA library. (B) Synthesized TRP genes. Lane 1: Sj1TR; Lane 2: Sj2TR; Lane 3: Sj4TR; Lane 4, Sj7TR. M = Marker. (C–G) Expression and purification of the recombinant proteins. M = Marker. Lane 1: Escherichia coli culture before adding isopropyl-thio-β-D-galactoside (IPTG) and Lane 2: after adding IPTG. (C) SjTPx-1. (D) Sj1TR. (E) Sj2TR. (F) Sj4TR. (G) Sj7TR.

Figure 2.

Enzyme-linked immunosorbent assay (ELISA) results of soluble egg antigen (SEA) and the recombinant antigens. (A) Negative serum samples from Japanese volunteers. (B) Negative endemic controls from Filipino volunteers. (C) Schistosoma japonicum stool-positive serum samples. (D) Post-treatment negative serum samples. (E) Sera positive for other heminthic infection (Paragonimus westermani, N = 11; Opisthorchis viverrini, N = 10; Trichuris trichiura, N = 1). (F) Sera positive for protozoan infection (Plasmodium falciparum, N = 3; Plasmodium vivax, N = 1; Entamoeba histolytica, N = 4). Mean optical density (OD) values (x) are given on each category of samples.