Identification of antigen-specific residues on E2 glycoprotein of classical swine fever virus

Envelope glycoprotein E2 of classical swine fever virus (CSFV) is the major antigen that induces neutralizing antibodies in infected pigs. Our previous study revealed that N-terminal 90 residues (domains B/C) of E2 play key roles in differentiating vaccine strain LPC/AHRI (subgroup 1.1) from the two field strains TD/96/TWN (subgroup 2.1) and 94.4/IL/94/TWN (subgroup 3.4) (Chang et al., 2010). This study further analyzed the reaction patterns between monoclonal antibodies (mAbs) and expressed hybrid N-terminal of E2 of the abovementioned viruses, revealing that mAbs T33 and C2, mAbs V8 and T23, and mAbs L7 and L150 required binding sites specifically at residues 690–714 in domain B, residues 715–740 in domain C, and residues 741–765 in domain C, respectively. Site-directed mutagenesis further demonstrated that residues 713E and 729D were critical for antigenic specificity of field strain (94.4/IL/94/TWN), while residues 705D and 761K were specific for vaccine strain (LPC/AHRI). These specific residues likely mediated in determining the topography of mAb binding sites of E2 to allow for differentiation between strains based on the premise that the structural integrity of the conformational epitope is maintained.