Evaluation of recombinant serine protease inhibitor from Trichinella spiralis for immunodiagnosis of swine trichinosis

Serine protease inhibitors, known as serpins, are mainly expressed in newborn and early-stage Trichinella spiralis larvae, suggesting that T. spiralis serpin (TsSERP) could be used as antigen for the immunodiagnosis of swine trichinosis. We produced His-tagged recombinant TsSERP (rTsSERP) in Escherichia coli and purified it using a Co(2+)-affinity column. Western blot (WB) and enzyme-linked immunosorbent assay (ELISA) were performed to determine T. spiralis-infected swine sera samples (n = 5), negative controls (n = 26), and other parasite-infected samples (n = 83). WB showed that T. spiralis-infected sera initially reacted with rTsSERP at day 6 post-infection (dpi), and more strongly in late infection (62 and 84 dpi). However, other parasite-infected sera also elicited cross-reactivity to rTsSERP. On the other hand, indirect ELISA showed that TsSERP was an appropriate antigen for detecting late (> 60 dpi) but not early infection. No cross-reaction was observed with other parasite-infected sera. Sensitivity and specificity of TsSERP-ELISA at 62 dpi was 80% and 100%, respectively, and at 84 dpi 100% and 100%, respectively. These preliminary results show that TsSERP-ELISA method is suitable for the diagnosis of swine trichinosis, and could become the standard test for diagnosis of trichinosis in several hosts, including humans.