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Porcine circovirus type 2 (PCV2) is recognized as a key infectious agent in post-weaning multisystemic wasting syndrome (PMWS), but not all pigs infected with PCV2 will develop PMWS.The aim of this work was to explore the relationships between PCV2 infection, oxidative stress and selenium in a PK-15 cell culture model of PCV2 infection.The results showed that oxidative stress induced by H2O2 treatment increased PCV2 replication as measured by PCV2 DNA copies and the number of infected cells.Furthermore, PCV2 replication was inhibited by selenomethionine (SeMet) at a high concentration (6μM) and the increase in PCV2 replication by oxidative stress was blocked by SeMet at physiological concentrations (2 or 4 μM).PCV2 infection caused a decrease of glutathione peroxidase 1 (GPx1) activity but an increase of GPx1 mRNA levels, suggesting that GPx1 may represent an important defense mechanism during PCV2 infection.SeMet did not significantly block the promotion of PCV2 replication in GPx1-knockdown cells.This observation correlates with the observed influence of SeMet on GPx1 mRNA and activity in GPx1-knockdown cells, indicating that GPx1 plays a key role in blocking the promotion of PCV2 replication.We conclude that differences in morbidity and severity of PMWS caused on different pig farms may be related to variations in oxidative stress and that selenium has a potential role in control of PCV2 infection.