Recombinant expression of the fusion antigen based on Treponema pallidum TpN17 and TpN47 epitope peptides and establishment and application of the associated ELISA

Abstract:

Using recombinant TpNs proteins of Treponema pallidum as antigens, ELISAs are proved to be of higher sensitivity and specificity. However, they can be further increased by using multiple TpNs antigens. According to the epitope analysis, we firstly used linking primers PCRs to obtain an artificial fusion gene segment tpE17-47 containing epitopes of both TpN17 and TpN47. Subsequently, we conducted the prokaryotic expression systems of entire tpN17 and tpN47 genes and tpE17-47 fusion gene. SDS-PAGE analysis and BioRad Gel Image Analysis System showed that the recombinant proteins rTpN17, rTpN47 and rTpE17-47 expressed stably, with 36%, 20% and 28% yields of total bacterial protein, respectively. After purified by Ni-NTA affinity chromatography, all the three recombinant proteins could be recognized by T. pallidum antibody positive sera from syphilis patients. The positive rate of rTpE17-47-ELISA for detecting serum specimens in clinically 630 cases with syphilis was 98.6%. This rate was slightly higher than that by Treponema pallidum particle agglutination (TPPA) (97.9%) (P>0.05), but significantly higher than those by rTpN17-ELISA (83.8%), rTpN47-ELISA (83.3%) and rapid plasma reagin (RPR)(72.1%)(P<0.01). Furthermore, both ELISAs and TPPA for detecting the serum specimens in 25 cases with SLE, 36 cases with RA and 250 healthy cases were all negative. RPR showed positive in 1 case with SLE, 2 cases with RA and 2 healthy cases. This could be a novel serological screening or diagnostic method of syphilis with advantages of quickness, convenience, safety, sensitivity and specificity.