Whereas no evident increase in the frequency of Tregs was observed in pigs infected with virulent PR40/2014 and SU1 PRRSV-1 strains in comparison with low virulent strains (26, 27), our research group already described an increase in FOXP3 expression in the lung from Lena-infected pigs at 2 weeks post-infection (18). Here, FOXP3 is linked to infection.