Identification of an immunodominant neutralizing epitope of porcine Deltacoronavirus spike protein

Abstract

Porcine deltacoronavirus (PDCoV) is a novel swine enteropathogenic coronavirus that, because of its broad host range, poses a potential threat to public health. Here, to identify the neutralizing B-cell epitopes within the S1-CTD protein, we generated three anti-PDCoV monoclonal antibodies (mAbs). Of these, the antibody designated 4E-3 effectively neutralized PDCoV with an IC50 of 3.155 μg/mL. mAb 4E-3 and one other, mAb 2A-12, recognized different linear B-cell epitopes. The minimal fragment recognized by mAb 4E-3 was mapped to ²⁸⁰FYSDPKSAV²⁸⁸ and designated S^280-288, the minimal fragment recognized by mAb 2A-12 was mapped to ⁵⁰⁶TENNRFTT⁵¹³, and designated S^506-513. Subsequently, alanine (A)-scanning mutagenesis indicated that Asp²⁸³, Lys²⁸⁵, and Val²⁸⁸ were the critical residues recognized by mAb 4E-3. The S^280-288 epitope induces PDCoV specific neutralizing antibodies in mice, demonstrating that it is a neutralizing epitope. Of note, the S^280-288 coupled to Keyhole Limpet Hemocyanin (KLH) produces PDCoV neutralizing antibodies in vitro and in vivo, in challenged piglets it potentiates interferon-γ responses and provides partial protection against disease. This is the first report about the PDCoV S protein neutralizing epitope, which will contribute to research of PDCoV-related pathogenic mechanism, vaccine design and antiviral drug development.

Keywords: Monoclonal antibody; Neutralizing epitope; Porcine deltacoronavirus.