Correlation between the IgG/IgA Antibody Response against PEDV Structural Protein and Virus Neutralization

Abstract

Porcine epidemic diarrhea (PED) is a highly contagious intestinal infectious disease caused by porcine epidemic diarrhea virus (PEDV). Large-scale outbreaks of PEDV have caused huge economic losses to the pig industry since 2010. Neutralizing antibodies play a pivotal role in protecting piglets from enteric infections. However, there has been no systematic report on the correlations between neutralizing antibody titers (NTs) and absorbance values of IgG or IgA to all PEDV individual structural proteins in clinical serum, fecal, and colostrum samples. In this study, the spike protein S1 domain (S1), membrane protein (M), envelope protein (E), and nucleocapsid protein (N) of the variant PEDV strain AH2012/12 were expressed and purified by using the human embryonic kidney (HEK) 293F expression system. A total of 92 clinical serum samples, 46 fecal samples, and 33 colostrum samples were collected, and the correlations between IgG or IgA absorbance values and NTs were analyzed. R² values revealed that anti-S1 IgA absorbance values show the highest agreement with NTs in all serum, fecal, and colostrum samples, followed by the N protein. The correlations between anti-E or M IgA and NTs were very low. However, in the colostrum samples, both IgG and IgA to S1 showed high correlations with NTs. In addition, compared with E and M, the highest correlations of IgA absorbance values were with N and S1 in serum and fecal samples. Overall, this study revealed the highest correlation between NTs and IgA to PEDV S1 protein. Therefore, the diagnostic method with anti-S1 IgA can be used as a powerful tool for assessing the immune status of pigs. IMPORTANCE The humoral immune response plays an important role in virus neutralization. Against PEDV, both IgG and the mucosal immune component IgA play roles in virus neutralization. However, which plays a more prominent role and whether there are differences in different tissue samples are not clearly reported. Additionally, the relationship between IgG and IgA against individual structural proteins and viral neutralization remains unclear. In this study, we systematically determined the relationship between IgG and IgA against all PEDV structural proteins and viral neutralization in different clinical samples and found the highest correlation between neutralization activity and IgA to PEDV S1 protein. Our data have important guiding implications in the evaluation of immune protection.

Keywords: IgA; IgG; PEDV; S1; neutralizing antibody titers.

FIG 1

Expression and purification of the PEDV S1, E, M, and N proteins. (A) IF assays of 293T cells transfected with eukaryotic plasmids pPEDV-S1, pPEDV-E, pPEDV-M, or pPEDV-N. (B) SDS-PAGE analyses of purified PEDV S1, E, M, and N according to the Materials and Methods. (C) Western blotting of purified PEDV S1, E, M, and N proteins using anti-His tag antibody; scale bars, 100 μm; M, protein maker; 1, pPEDV-S1; 2, pPEDV-N; 3, pPEDV-M; 4, pPEDV-E.

FIG 2

(A and B) Correlations of NTs with IgG (A) or IgA (B) OD values for S1, E, M, and N in sera. Correlations are shown in scatterplots and line charts. For scatterplots, the x axis indicates the NTs, and the y axis indicates the antibody OD values. For line charts, the x axis indicates the number of samples, the left axis indicates NTs, and the right axis indicates the antibody OD values. R² values represent the correlation coefficients.

FIG 3

(A and B) Correlations of NTs with IgG (A) or IgA (B) OD values for S1, E, M, and N in fecal samples. Correlations are shown in scatterplots and line charts. For scatterplots, the x axis indicates the NTs, and the y axis indicates the antibody OD values. For line charts, the x axis indicates the number of samples, the left axis indicates NTs, and the right axis indicates the antibody OD values. R² values represent the correlation coefficients.

FIG 4

Correlations of NTs with IgG or IgA OD values for S1 in colostrum samples. Correlations are shown in scatterplots and line charts. For scatterplots, the x axis indicates the NTs, and the y axis indicates the antibody OD values. For line charts, the x axis indicates the number of samples, the left axis indicates NTs, and the right axis indicates the antibody OD values. R² values represent the correlation coefficients.

FIG 5

(A and B) Correlations of IgA OD values of E, M, and N with IgA OD values of S1 in serum and fecal samples. Correlations of the IgA OD values of E, M, and N to the IgA OD values of S1 in serum (A) and fecal (B) samples are shown. Correlations are shown in scatterplots. R² values represent the correlation coefficients.