IFNG and coinfection: Co-infection with other infectious agents, such as porcine parvovirus (PPV) (Allan et al., 1999), porcine reproductive and respiratory syndrome virus (PRRSV) (Allan et al., 2000) and Mycoplasma hyopneumoniae (Opriessnig et al., 2004), or stimulation with non-infectious agents, such as lipopolysaccharide (Chang et al., 2006), concanavalin A (Lefebvre et al., 2008) and the interferons IFN-α/IFN-γ (Ramamoorthy et al., 2009), remarkably enhanced PCV2 replication in vitro or in vivo.