FASLG and susceptibility to pneumonia measurement: Taken together, the increased expression of IFN-α, TNF-α, IL-8, and FasL mRNA in AMs from pigs in various infection orders by PCV2 and PRRSV observed in the present study, to some extent may contribute to pneumonia and bronchiolar epithelial damage in the lungs of PCV2- and/or PRRSV-infected pigs.