Immune Molecules’ mRNA Expression in Porcine Alveolar Macrophages Co-Infected with Porcine Reproductive and Respiratory Syndrome Virus and Porcine Circovirus Type 2

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus 2 (PCV2) are economically important pathogens in swine, and pigs with dual infections of PCV2 and PRRSV consistently have more severe clinical symptoms and interstitial pneumonia. However, the synergistic pathogenesis mechanism induced by PRRSV and PCV2 co-infection has not yet been illuminated. Therefore, the aim of this study was to characterize the kinetic changes of immune regulatory molecules, inflammatory factors and immune checkpoint molecules in porcine alveolar macrophages (PAMs) in individuals infected or co-infected with PRRSV and/or PCV2. The experiment was divided into six groups: a negative control group (mock, no infected virus), a group infected with PCV2 alone (PCV2), a group infected with PRRSV alone (PRRSV), a PCV2–PRRSV co-infected group (PCV2–PRRSV inoculated with PCV2, followed by PRRSV 12 h later), a PRRSV–PCV2 co-infected group (PRRSV–PCV2 inoculated with PRRSV, followed by PCV2 12 h later) and a PCV2 + PRRSV co-infected group (PCV2 + PRRSV, inoculated with PCV2 and PRRSV at the same time). Then, PAM samples from the different infection groups and the mock group were collected at 6, 12, 24, 36 and 48 h post-infection (hpi) to detect the viral loads of PCV2 and PRRSV and the relative quantification of immune regulatory molecules, inflammatory factors and immune checkpoint molecules. The results indicated that PCV2 and PRRSV co-infection, regardless of the order of infection, had no effect on promoting PCV2 replication, while PRRSV and PCV2 co-infection was able to promote PRRSV replication. The immune regulatory molecules (IFN-α and IFN-γ) were significantly down-regulated, while inflammatory factors (TNF-α, IL-1β, IL-10 and TGF-β) and immune checkpoint molecules (PD-1, LAG-3, CTLA-4 and TIM-3) were significantly up-regulated in the PRRSV and PCV2 co-infection groups, especially in PAMs with PCV2 inoculation first followed by PRRSV. The dynamic changes in the aforementioned immune molecules were associated with a high viral load, immunosuppression and cell exhaustion, which may explain, at least partially, the underlying mechanism of the enhanced pulmonary lesions by dual infection with PCV2 and PRRSV in PAMs.

Integrative transcriptomic profiling of mRNA, miRNA, circRNA, and lncRNA in alveolar macrophages isolated from PRRSV-infected porcine

“…This might be indicative of the commencement of recovery mechanisms in pigs from PRRS, suggesting a potential temporal modulation of these genes during the infection’s progression. These findings align with three other investigations, which report CTLA4 upregulation during PRRSV-1 or PRRSV-2 infection ( 59 – 61 ), lending further credence to the prolonged immune suppressive effect of PRRSV. We also observed the upregulation of another gene, SAMHD1 (SAM domain and HD domain-containing protein 1), known for its antiviral properties triggered by interferon, and its capacity to restrain the proliferation of numerous RNA or DNA viruses ( 62 , 63 ).…”

Porcine Circovirus Type 3 (PCV3) in Poland: Prevalence in Wild Boar Population in Connection with African Swine Fever (ASF)

“…This finding complements earlier reports showing that coinfection with PCVs may favor the development or enhance the course of the other diseases [36]. Swine circoviruses have tropism to the lymphoid tissue of the host, thereby leading to immunosuppression and an increased tendency to secondary infections [41]. Moreover, it has been demonstrated that PCV2 and PRRSV coinfection promoted PRRSV replication in PAM cells.…”

“…Moreover, it has been demonstrated that PCV2 and PRRSV coinfection promoted PRRSV replication in PAM cells. The downregulation of immune regulatory factors (IFN-α and IFN-γ) and the upregulation of inflammatory factors (TNF-α, IL-1β, IL-10, and TGF-β) and immune checkpoint molecules (PD-1, LAG-3, CTLA-4, and TIM-3) were observed in the cells where PRRSV infection was preceded by PCV2 [41]. Consistent with these reports, our results suggest that primary PCV3 infection, similar to PCV2, may play a role in susceptibility to the other viruses, including ASFV.…”