Following primary infection of 5-6 week old piglets (RE and TC groups), the initial IFN-γ responses were moderate with around 50% of the pigs responding with Ag-specific IFN-γ above background level (100 pg/mL), and with several pigs showing a sustained high Ag-specific IFN-γ response even at day 48 pi. This evidence concerns the gene IFNG and infection.