Thus, the present work evaluates the relative expression of costimulatory (CD28, CD226, TNFRSF9, SELL, ICOS and CD40) and coinhibitory (CTLA4, TIGIT, PD1/PDL1 axis, TIM3, LAG3, and IDO1) molecules in lung and tracheobronchial lymph node upon an experimental infection with two PRRSV-1 strains of different virulence, virulent Lena and low virulent 3249 strains, during the first 2 weeks post-infection. Here, ICOS is linked to infection.