Reactivity of Porcine Epidemic Diarrhea Virus Structural Proteins to Antibodies against Porcine Enteric Coronaviruses: Diagnostic Implications

Abstract

The development of porcine epidemic diarrhea virus (PEDV) antibody-based assays is important for detecting infected animals, confirming previous virus exposure, and monitoring sow herd immunity. However, the potential cross-reactivity among porcine coronaviruses is a major concern for the development of pathogen-specific assays. In this study, we used serum samples ( = 792) from pigs of precisely known infection status and a multiplex fluorescent microbead-based immunoassay and/or enzyme-linked immunoassay platform to characterize the antibody response to PEDV whole-virus (WV) particles and recombinant polypeptides derived from the four PEDV structural proteins, i.e., spike (S), nucleocapsid (N), membrane (M), and envelope (E). Antibody assay cutoff values were selected to provide 100% diagnostic specificity for each target. The earliest IgG antibody response, mainly directed against S1 polypeptides, was observed at days 7 to 10 postinfection. With the exception of nonreactive protein E, we observed similar antibody ontogenies and patterns of seroconversion for S1, N, M, and WV antigens. Recombinant S1 provided the best diagnostic sensitivity, regardless of the PEDV strain, with no cross-reactivity detected against transmissible gastroenteritis virus (TGEV), porcine respiratory coronavirus (PRCV), or porcine deltacoronavirus (PDCoV) pig antisera. The WV particles showed some cross-reactivity to TGEV Miller and TGEV Purdue antisera, while N protein presented some cross-reactivity to TGEV Miller. The M protein was highly cross-reactive to TGEV and PRCV antisera. Differences in the antibody responses to specific PEDV structural proteins have important implications in the development and performance of antibody assays for the diagnosis of PEDV enteric disease.

Specific recombinant proteins of porcine epidemic diarrhea virus are immunogenic, revealing their potential use as diagnostic markers

“…All data were processed using SPSS (version 20.0) software and the GraphPad Prism program as described previously (Gimenez-Lirola et al, 2017;Huang et al, 2012).…”

“…Therefore, the eukaryotic-expressed S1 protein is likely more advantageous than the WV as the antigen for PEDV serological assays. For another two major structural proteins M and N, due to common epitopes shared by PEDV, TGEV and PDCoV, several studies have previously demonstrated that PEDV M or N presented some cross-reactivity to TGEV or PDCoV (Gimenez-Lirola et al, 2017;Lin et al, 2015;Ma et al, 2016). In contrast, recombinant PEDV-S1 had no cross-reactivity with sera from these porcine coronaviruses, showing the best diagnostic sensitivity (Gimenez-Lirola et al, 2017).…”

“…Another common diagnostic method is serological testing for the presence of specific antibodies against viral proteins, which is also fast and convenient for epidemiologic investigations. Many tools have been developed for the detection of anti-PEDV antibodies based upon the major structural proteins (such as S, M or N proteins) in serum, colostrum, milk, feces and oral fluid, including indirect immunofluorescence assays (IFA), virus neutralization assays (SN), enzyme-linked immunosorbent assays (ELISA), and fluorescent microsphere immunoassays (FMIA) (Diel et al, 2016;Gerber et al, 2014;Gerber and Opriessnig, 2015;Gimenez-Lirola et al, 2017;Okda et al, 2015). But comparative studies of the above assays using different PEDV structural and nonstructural proteins as antigens are rarely conducted.…”

Porcine epidemic diarrhea virus (PEDV) introduction into a naive Dutch pig population in 2014

“…All animals that have been infected with PEDV have antibodies against the S protein and particularly against the S1part. The S1-part of the spike protein is the most variable part between related coronaviruses and there is no cross reactivity with other coronaviruses such as Transmissible gastroenteritis coronavirus (TGEV), Porcine respiratory coronavirus (PRCoV) and Porcine Delta Coronavirus (PDCoV) as previously described (Gimenez-Lirola et al, 2017;Lin et al, 2015b). Because results of immunoassays based on the S protein correlate well with viral neutralization (Paudel et al, 2014), as shown in Supplementary Table 1, we decided to use the VNT as an alternative sero-diagnostic assay.…”

Emerging and re-emerging coronaviruses in pigs

“…Serum PEDV IgG Ab responses were studied in seven-week-old conventional pigs inoculated with non-S INDEL PEDV via the oragastric route at À7 to 42 days post-inoculation (dpi). IgG antibodies were detected as early as 7 dpi for the S1 subunit of the S protein and 10 dpi for the N and M structural proteins and the whole virus particles [90 ]. The antibody titers peaked at 14-17 dpi and remained detectable through 42 dpi.…”