Development of a blocking ELISA based on site 2 monoclonal antibodies and foot-and-mouth disease virus-like particles for seromonitoring vaccinated animals

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals worldwide. Serum neutralization test (SN test), a gold standard for evaluating the protection rate against FMDV, is still performed for disease control in Taiwan. However, SN test is laborious, expensive and requires a high-containment biosafety lab. Based on the current study on vaccinated animals, antigenic site 2 of FMDV is the most immuno-dominant neutralizing site. We aim to establish a blocking ELISA (bELISA) based on FMD virus-like particles (VLPs) and site 2 monoclonal antibody (MAb) to detect antibodies against site 2 from vaccinated animals and replace the SN test. VLPs were expressed by eukaryotic transient expression assay with co-transfect strategy and examined by sucrose gradient centrifugation accompanied with sandwich ELISA. For mapping MAb against site 2 from 41 anti-FMDV MAbs prepared previously, we performed knock-out mutagenesis with VLPs and mVLPs (site 2 mutated) by immunofluorescence assay (IFA) and indirect ELISA. Combined with neutralization assay, results indicated that 6 MAbs recognized site 2. Based on the results of sandwich ELISA and bELISA with experimental serum, S11E-9 was regarded as the best tracer to establish bELISA with VLPs.