Antigenicity Alternations of Variant PEDV S Protein Disclosed by Linear B Cell Epitope Mapping

The spike protein (S) plays a crucial role in porcine epidemic diarrhea virus (PEDV) infection and induces neutralizing antibodies. Mutations of the S protein are supposed to provide the main antigenic shift leading to the antigenic escape of PEDVs. It is therefore a significant question how much accumulation of antigenic shift could lead to the antigenic escape of the variant PEDV. To provide an answer in the study, B cell epitopes (BCEs) on the S protein of the PEDV vaccine strain CV777 (S-CV777) and variant strain SD2014 (S-SD2014) were mapped using biosynthetic peptides and rabbit anti-PEDV S serum. Seventy-nine and 68 linear BCEs were identified from S-CV777 and S-SD2014, respectively. While 66.2% of the BCEs of S-SD2014 could be recognized by anti-S-CV777 serum and 67.1% of S-CV777 BCEs could be recognized by anti-S-SD2014 serum, more than 40% of the BCEs identified using anti-S-CV777 serum on S-CV777 could not be recognized by anti-S-SD2014 serum and vice versa. The completely shared BCEs took low percentages of 29.4% and 25.3% for S-SD2014 and S-CV777, respectively. These results indicate a low conservation of antigenicity of the S protein compared to a relatively high amino acid sequence similarity of 92.2% between the two strains. The study provided a BCE shift reference of PEDV antigenic escape and surveillance control.