Therefore, the goal of this study was to evaluate the expression of selected immune checkpoints (PD1/PDL1, CTLA4, TIM3, LAG3, CD200R1 and IDO1) in the thymus of piglets infected with two PRRSV-1 strains (3249 and Lena) of different virulence and to determine their correlation with the disease course during the early stage of infection. This evidence concerns the gene PDCD1 and infection.