PDCD1 and infection: Previous studies have already pointed to an up-regulation of PD1/PDL1 axis in PRRSV-1 and PRRSV-2 infections (Richmond et al., 2015a,b; Chaudhari et al., 2020, 2021; Ruedas-Torres et al., 2021b), with decreased levels of apoptosis and anergy in porcine lymphocytes deficient in PD1 (Richmond et al., 2015b).