Changes in the levels of IL-8, TNF-α, and IFN-α production in the supernatants of swine alveolar macrophages (AMs). Changes in the levels of IL-8 (A), TNF-α (B), and IFN-α (C) produced in PCV2- and/or PRRSV-inoculated swine alveolar macrophages (AMs) were expressed as the level different from that of mock-inoculated AMs (Mock) and shown as mean ± SD of three independent experiments. 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 at the same h post inoculation (HPI) with the first virus. a, b, c, d, eValues with different labels at the same HPI differ significantly (P < 0.05).