The N-terminal domain of Spike protein contributes to antigenicity
difference between porcine epidemic diarrhea virus genotypes G1 and G2
Porcine epidemic diarrhea virus (PEDV) strains have been clarified into
two genotypes, G1 and G2, based on the sequence of the spike (S) gene.
Amino acid mutations that distinguish the two PEDV genotypes were mostly
located in the N-terminal domain (NTD) (aa 1-380) of S protein. The fact
of increased outbreaks of G2 subtype PEDV and the failure of G1 subtype
PEDV strain (CV777)-based vaccine in China since 2010 suggested that
multiple amino acid mutations located in the NTD altered the
antigenicity of S protein. To determine the role of the NTD of S protein
in the antigenicity difference, the NTD of the CV777 vaccine strain (G1)
and CH/ZMDZY/11 strain (G2) was expressed in E. coli, respectively.
polyclonal antibodies (PAbs) against genotype-specific S proteins were
prepared by immunizing BALB/c mice using purified S proteins.
Antigenicity was systematically compared by detection of PAbs against
two genotype PEDV strains and purified S proteins using Western blot,
indirect enzyme-linked immunosorbent assay (ELISA), indirect
immunofluorescence assay (IFA), and serum cross-neutralization assay
(SN). Consistent with the multiple amino acid mutations in the NTD of S
protein, different antigenic cross-reactivity between the two genotypes
was demonstrated. There was six-fold and more than twenty-fold
difference in ELISA and SN titer between anti-CV777 S protein antibodies
against G1 and G2 subtype strains, respectively. There was twofold and
eight-fold difference in ELISA and SN titer between anti-ZMDZY S protein
antibodies against G1 and G2 genotype strains, respectively. The results
proved that the NTD of S protein contributes to the antigenicity
difference between PEDV genotypes G1 and G2, and highlighted a G2 strain
should be used to develop a vaccine for providing better protection
against prevalent genotype of PEDV.