247. Based on the data, the cut-off was determined as 0.295 by ROC curve analysis, providing the best balance of sensitivity (100%) and specificity (98.4%). Evaluated by the cut-off, all 54 serum samples from FMDV infection cattle and all 20 serum samples from naive cattle were FMDV NSP antibody positive

and negative, respectively, whereas 131 out of 137 serum samples from vaccinated cattle were FMDV NSP antibody negative. To validate the performance of r3aB-ELISA, 118 serum samples derived from vaccinated cattle, 46 serum samples derived from infected cattle and 20 serum samples from naive cattle were tested by r3aB-ELISA and two commercial kits including UBI® NSP ELISA and Ceditest® FMDV-NS ELISA. As shown in Table 2, FMDV NSP antibodies were all negative in 20 serum samples from naive cattle, determined by three click here ELISA systems. 46 serum samples from infected cattle were positive for FMDV NSP antibodies tested by r3aB-ELISA. However, 1 and 2 samples in 46 sera of infected cattle were negative for FMDV NSP antibodies tested by UBI® NSP ELISA and Ceditest® FMDV-NS

ELISA, respectively. 5, 8 and 4 samples in 118 sera of vaccinated cattle were positive for FMDV NSP antibodies determined by r3aB-ELISA, UBI® NSP ELISA Akt inhibitor and Ceditest® FMDV-NS ELISA, respectively. Accordingly, the specificity [(positive sera + negative sera)/total tested sera × 100%] of the r3aB-ELISA, UBI® NSP ELISA and Ceditest® FMDV-NS ELISA were 97.3% (179/184), 95.1% (175/184) and 96.7% (178/184), respectively. When r3aB-ELISA was compared PD184352 (CI-1040) with UBI® FMDV-NS ELISA and Ceditest® NSP ELISA, the coincident rate was 97.8% (180/184) and 96.7% (178/184), respectively. In this study, a recombinant truncated FMDV non-structural protein 3AB (r3aB) was used to establish an indirect ELISA for distinguishing antibodies induced by FMDV infection from those induced by vaccination in cattle. FMD is the most important viral infectious disease of livestock and locally outbreaks endlessly worldwide because of some “carriers” with a long asymptomatic infection companying persistent virus replication and release

even though vaccination strategy has been adopted. To distinguish natural infection of FMDV from vaccination in animals is still necessary for early warning of FMD outbreak and medical inspection in export and import of livestock and their flesh products. Previously, recombinant 3AB (r3AB) was used to catch the antibodies from the sera of FMDV infected animals not the antibodies in the sera of the animals vaccinated by either inactivated FMDV vaccine or peptide vaccine. The r3AB displayed a good antigenicity when recognized by its antibodies but expressed in inclusion body in E. coli and appeared in monomers and dimers during purification. Upon analyzing the structural properties of 3AB using Hopp and Woods prediction method [20], we found that the 3AB was less hydrophilic at its N-terminals.