(C) Quantitative analysis of relative fluorescence intensity usingImageJ. showed that administering mAb 4A6 once or twice could delay the onset of diarrhea symptoms, reduce the severity of diarrhea, and decrease virus shedding. Taken together, our findings demonstrate that mAb 4A6 holds promise as a treatment against PDCoV, and the amino acids recognized by mAb 4A6 will be useful for developing novel epitope-based vaccines or antiviral drugs. == IMPORTANCE == Porcine deltacoronavirus (PDCoV) is a novel swine enteropathogenic coronavirus that poses a potential threat to public health. Developing effective antiviral therapies is crucial for its prevention and control. Here, we exhibited that mAb 4A6 shows promise as a treatment against PDCoV. Antibody therapy experiments conducted on PDCoV-infected piglets revealed that administering mAb 4A6 once or twice could delay the onset of diarrhea symptoms, reduce the severity of diarrhea, and decrease virus shedding. Furthermore, we characterized the conformational epitope (S461, P462, T463, E465, and Y467) recognized by mAb 4A6 through an integrated approach involving phage display peptide library, molecular docking, and alanine scanning mutagenesis. More importantly, mAb 4A6 exhibits a broad-spectrum neutralizing activity against different PDCoV Rabbit Polyclonal to EGFR (phospho-Ser695) strains. These findings show that mAb 4A6 has promising therapeutic value for PDCoV-infected piglets, and the identification of mAb 4A6 acknowledged epitope may provide a new idea for the identification of conformational epitopes. KEYWORDS:porcine deltacoronavirus, neutralizing monoclonal antibody, conformational epitope, Cordycepin therapy Cordycepin experiments, piglet model == INTRODUCTION == Coronaviruses (CoVs) are a diverse group of enveloped, single-stranded RNA viruses with the ability to infect both human and animal populations. One prominent example is usually severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was responsible for the COVID-19 pandemic (1). The virus is believed to Cordycepin have originated from bat coronaviruses (24) and to have jumped to humans through an intermediate animal host (5), although the exact host has yet to be definitively identified. Similarly, in 2012, Middle East respiratory syndrome CoV (MERS-CoV) emerged in Saudi Arabia (6), and although it has not established sustained human infections, it is recurrently re-emerged from its reservoir, the dromedary camel (7,8). These occurrences serve as poignant illustrations of CoVs ability to jump species and the ongoing risk to human and animal health. CoVs are classified into four genera:Alphacoronavirus,Betacoronavirus,Gammacoronavirus, andDeltacoronavirus. The first two genera cause infections only in mammals, while birds and mammals are commonly infected byGamma- andDelta-coronaviruses(9). Porcine deltacoronavirus (PDCoV) was first discovered in fecal samples of pigs in Hong Kong in 2012, though its origin remains unclear (9). Since its initial detection, PDCoV has been widely reported in the Americas and Asia and has become a common pathogen in pig populations (1017). PDCoV infects intestinal epithelial cells and causes serious diarrhea, vomiting, dehydration, and mortality in suckling piglets. Symptomatic PDCoV infection has also been observed in calves, chickens, poults, and mice in experimental settings (1821), an indication of the wide host range potential. In 2021, PDCoV was detected in plasma samples from three children with acute febrile illness (22). This discovery raises public health concerns about PDCoV transmission from swine to humans. The initial step in CoV infection involves the binding of the viral spike (S) protein to a receptor on the host cell surface (23). The S protein is also the primary target of the humoral immune response during infection. Buchhol et al. (24) report that a single intranasal administration of parainfluenza virus type 3 vector expressing the SARS-CoV S protein produced high levels of neutralizing antibodies, comparable to those from SARS-CoV infection. Because of its significant role in infection, the S.