Hence, this study aims to evaluate the expression of some costimulatory (CD28, CD226, TNFRSF9, SELL, ICOS and CD40) and coinhibitory (CTLA4, TIGIT, PD1/PDL1 axis, TIM3, LAG3, and IDO1) molecules in the lung and tracheobronchial lymph node from piglets infected with two PRRSV-1 strains of different virulence, virulent Lena strain and low virulent 3249 strain, during the early stage of infection. Here, IDO1 is linked to infection.