Expression levels of FasL mRNA in PCV2- and/or PRRSV-inoculated swine alveolar macrophages (AMs). The expression levels of FasL mRNA in all cultures were analyzed at 42 h after inoculation with the first virus by RT-PCR and electrophoresis. The sizes of FasL and GAPDH housekeeping gene are 366 and 96 b.p., respectively (A); values are further normalized using the housekeeping gene GAPDH and expressed as the relative intensity at the level different from that of mock-inoculated AMs (Mock) and shown as mean ± SD of three independent experiments (B). Mock: AMs inoculated with an equal volume of RPMI-C; PCV2: AMs inoculated with PCV2 alone; PRRSV: AMs inoculated with PRRSV alone; PCV2/PRRSV: AMs inoculated with PCV2 first then inoculated with PRRSV 18 h later; PRRSV/PCV2: AMs inoculated with PRRSV first then inoculated with PCV2 18 h later; PCV2-PRRSV: AMs co-inoculated with PCV2 and PRRSV simultaneously. *Significantly different (P < 0.05) from the Mock. a, b, cValues with different labels differ significantly (P < 0.05).