Viral respiratory diseases remain problematic in swine. Among viruses, porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus (SIV), alone or in combination, are the two main known contributors to lung infectious diseases. Previous studies demonstrated that experimental dual infections of pigs with PRRSV followed by SIV can cause more severe disease than the single viral infections. However, our understanding of the impact of one virus on the other at the molecular level is still extremely limited. Thus, the aim of the current study was to determine the influence of dual infections, compared to single infections, in porcine alveolar macrophages (PAMs) and precision cut lung slices (PCLS). PAMs were isolated and PCLS were acquired from the lungs of healthy 8-week-old pigs. Then, PRRSV (ATCC VR-2385) and a local SIV strain of H1N1 subtype (A/Sw/Saskatchewan/18789/02) were applied simultaneously or with 3h apart on PAMs and PCLS for a total of 18 h. Immuno-staining for both viruses and beta-tubulin, real-time quantitative PCR and ELISA assays targeting various genes (pathogen recognition receptors, interferons (IFN) type I, cytokines, and IFN-inducible genes) and proteins were performed to analyze the cell and the tissue responses. Interference caused by the first virus on replication of the second virus was observed, though limited. On the host side, a synergistic effect between PRRSV and SIV co-infections was observed for some transcripts such as TLR3, RIG-I, and IFNβ in PCLS. The PRRSV infection 3h prior to SIV infection reduced the response to SIV while the SIV infection prior to PRRSV infection had limited impact on the second infection. This study is the first to show an impact of PRRSV/SIV co-infection and superinfections in the cellular and tissue immune response at the molecular level. It opens the door to further research in this exciting and intriguing field.

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The understanding of innate immune modulation by pathogens and immune-modulating agents, including synthetic oligodeoxynucleotides (CpG ODNs), has offered several new approaches to improve prophylactic and therapeutic strategies against infectious diseases in humans and animals. However, in this regard not much work has been done in avian medicine. In the present study, we analyzed the kinetics of interferon (IFN), cytokine, and chemokine mRNA expression in chicken embryonic spleen at 6 hr, 24 hr, 48 hr, and 72 hr after administration of CpG ODN 2007 (B-class) in 18-day-old chicken embryos. Our data showed enhanced expression of IFN-gamma; interleukin (IL)-1 beta, IL-6, and IL-8; and oligoadenyl synthetase A mRNA after CpG ODN administration. In addition, CpG ODN administration to chicken embryos 24 hr before the challenge with infectious bronchitis virus (IBV) was capable of limiting IBV propagation in different embryonic tissues. Based on the kinetics and type of cytokines induced after in ovo administration of CpG ODN, it may be speculated that in ovo administration of CpG ODNs may enhance resistance from viral infection in neonatal chicks and that CpG ODNs may contribute toward the development of more effective and safer poultry vaccines including in ovo vaccines.

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