| Classical swine fever (CSF), also known as hog cholera, one of OIE-listed diseases, is caused by Classical swine fever virus (CSFV). CSF is a highly contagious disease of pigs. In recent years, CSF has changed a lot in clinical manifestations under the pressure of mass vaccination in China, resulting in atypical or chronic forms quite different from acute CSF, and causing great economic losses in pork industry. Extensive vaccination with C-strain (lapinized hog cholera vaccine, HCLV) makes it difficult to differentiate the animals infected with wild-type viruses from those vaccinated with C-strain vaccine using conventional assays.The envelope glycoprotein E2 of CSFV is responsible for the elicitation of neutralizing antibodies. It is often used for developing new type vaccines, clinical diagnostic reagents and studying immunopathological mechanisms of the virus.CSFV E2 gene was codon-optimized according to the Sf9 cell codon usage. The codon-optimized E2 gene was expressed in insect baculovirus expression system, with expression level of 3 times higher than that of the wild-type E2 gene. On the other hand, rabbits immunized with E2 protein can be protected from challenge with HCLV.A monoclonal antibody (mAb) specifically directed against the E2 protein of wild-type CSFV was generated using the recombinant baculovirus-expressed E2 protein of C-strain (HCLV-E2) as tolergen and that of Shimen strain (Shimen-E2) as immunogen using chemical-induced immunosuppression. Cyclophosphamide was used to tolerize mice to HCLV-E2 followed by immunization with Shimen-E2. The mAb was shown to recognize CSFV Shimen strain, but not C-strain. The mAb showed neutralizing activity with several subgroups of wild-type CSFV in neutralizing immunofluorescence assay. The mAb was shown to recognize a conformational epitope on the E2 protein. The mAb was identified to be IgG1 subtype. The mAb can be used to differentiate wild-type CSFV strains from C-strain.
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