Replication kinetics of different porcine circovirus 2 strains in PK-15 cells, fetal cardiomyocytes and macrophages

In this in vitro study, the replication kinetics of porcine circovirus type 2 (PCV2) in porcine alveolar macrophages (PAM) and fetal cardiomyocytes (FCM), two target cells in vivo, was compared with that in PK-15 cells. Cultures were inoculated with either the postweaning multisystemic wasting syndrome (PMWS)-associated strain Stoon-1010 or the abortion-associated strain 1121. Viral proteins were visualized and virus production was determined. In PK-15 cells, the capsid protein was expressed between 6 and 12 hours post inoculation (hpi), it relocated to the nucleus between 12 and 24 hpi. At that time, Rep protein was also detected in the nucleus. This sequence of events also occurred in FCM and PAM but nuclear localized antigens appeared later (48 hpi) and in a lower percentage of cells. In PAM, clear differences in susceptibility were seen between pigs. In PAM from two out of five tested pigs, nuclear localized antigens were not detected, whereas in PAM from three other pigs they were seen in up to 20% of the antigen-positive cells. Virus production was observed in PK-15 but not in PAM or FCM cultures. In a second study, the replication kinetics of seven different PCV2 strains were compared in PK-15 cells. It was shown that the two abortion-associated strains had a different replication kinetics in comparison with PMWS or porcine dermatitis and nephropathy syndrome associated strains. With the abortion-associated strains, a higher number of infected cells was observed at 24 hpi and the percentage of infected cells with nuclear localised antigens was lower compared to that of other strains.