PDCD1 and coinfection: In this sense, up-regulation of PD-1/PD-L1 axis and its association with apoptosis has been suggested in CSFV-infected pigs (14) as well as in in vitro experimental infections with some strains of PCV2 and PRRSV-2 and PCV2/PRRSV-2 co-infection (15, 16).