Development and evaluation of two truncated recombinant NP antigen-based indirect ELISAs for detection of bovine parainfluenza virus type 3 antibodies in cattle.

Abstract Bovine parainfluenza virus type 3 (BPIV3) is one of the most important viral respiratory pathogens in both young and adult cattle. Nucleocapsid protein (NP) is the most abundant viral protein and the main regulator of virus replication and transcription. In this study, amino acid sequence data of BPIV3 NP was used to identify potential linear epitopic regions, which were subsequently used to design truncated recombinant NP antigens. The amino-terminal region (aa 9-157, NP-N) and the carboxy-terminal region (aa 391-500, NP-C) were selected, and these two truncated recombinant BPIV3 NP proteins were expressed in Escherichia coli based on the results of prediction studies. Furthermore, Enzyme-Linked Immunosorbent Assays (ELISAs) were established using the truncated recombinant BPIV3-N proteins as antigens, and 154 clinical samples were used to evaluate the newly established ELISA systems in comparison with a virus neutralisation test (VNT) as a reference. The results showed that a high coincidence rate was observed for the data that were obtained by the two methods. The sensitivity of NP-N ELISA and NP-C ELISA were 98.4% and 94.6%, respectively, and the specificity of both ELISAs was 100% with reference to the VNTs. Our data indicated that both ends of NP have high immunogenicity during BPIV3 infection and that they were good targets for serodiagnosis. The ELISAs based on the two truncated proteins were especially suitable for use in large-scale epidemiological investigations.