DETECTION OF ANTIBODIES AGAINST CLASSICAL SWINE FEVER VIRUS IN SWINE SERA BY INDIRECT ELISA USING RECOMBINANT ENVELOPE GLYCOPROTEIN E2

Recombinant envelope protein E2 (gp55) of classical swine fever virus (CSFV) strain Alfort/187 was evaluated as an alternative to whole viru s as ELISA antigen for the detection of antibodies against CSFV. A gly cosylated and a non-glycosylated form of E2 was expressed in the bacul ovirus system. Six histidine residues added at the carboxy terminus of each of the recombinant proteins allowed purification by nickel-chela te affinity chromatography. Comparison of the antigenic properties of the two proteins in indirect and blocking ELISAs revealed that the gly cosylated form resulted in both higher sensitivity and specificity. Th e indirect ELISA, using glycosylated E2, either derived from crude cel l extract or affinity-purified, was validated by testing a total of 27 19 porcine sera. Its final version proved to be as sensitive (98.3%) a s the virus neutralization test when sera from infected pig herds were examined, and highly specific (99.6%) when applied to test negative s era. It is therefore suitable for large scale monitoring of classical swine fever.