In vitro expression, monoclonal antibody and bioactivity for capsid protein of porcine circovirus type II without nuclear localization signal

We expressed firstly the Capsid protein gene defecting the nuclear localization signal (NLS) of Porcine circovirus type II (PCV2) in Escherichia coli as a fusion protein with glutathione S-transferase (rGST-dCap protein). The purified rGST-dCap protein and the recombinant NLS-defected Cap protein of PCV2 (rdCap protein) from the purified rGST-dCap protein reacted specifically with swine antiserum to PCV2. Furthermore, the obtained monoclonal antibodies (mAbs) to rdCap protein were shown to bind to PCV2 particles replicated in PK15 cell and capsid protein (Cap protein) of PCV2 expressed in PK15 cells, respectively. mAbs to rdCap protein also revealed the neutralizing ability to PCV2 particles. These results demonstrated that rGST-dCap protein expressed in E. coli was folded correctly or at least partly, and mAbs to rdCap protein possessed the binding epitopes of PCV2 particles whereas mAbs 4C4 and 3F6 to rdCap protein remained the neutralization epitope of PCV2 particle, showing a possibility of neutralizing mAb to rdCap protein as an immnuotherapeutic agent and a potential of rGST-dCap protein as a vaccine antigen or serodiagnostic reagent.