A clinically attenuated double-mutant of porcine reproductive and respiratory syndrome virus-2 that does not prompt overexpression of proinflammatory cytokines during co-infection with a secondary pathogen

• Published in: PLoS pathogens Vol. 20; no. 3; p. e1012128
• Main Authors: Su, Chia-Ming, Kim, Jineui, Tang, Junyu, Hung, Yu Fan, Zuckermann, Federico A., Husmann, Robert, Roady, Patrick, Kim, Jiyoun, Lee, Young-Min, Yoo, Dongwan
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 28.03.2024; Public Library of Science (PLoS)
• Subjects: Adaptive immunity; Alveoli; Amino acids; Analysis; Animal diseases; Animals; antagonists; Antibodies; B cells; Bacteria; Bacterial infections; Betaarterivirus suid 2; Biological response modifiers; Biology and Life Sciences; Care and treatment; Chemokines; Coronaviruses; Cytokines; Diagnosis; disease severity; domain; Gene expression; Gene mutations; genes; Genetic aspects; genetic engineering; Genetic modification; Genetically modified organisms; Genetics; Genomes; Health aspects; Immunology; Infection; Infections; Inflammation; Interferon; interferons; Leucine; Livestock farms; Localization; Lymphocytes; Macrophages; Medical research; Medicine and Health Sciences; Medicine, Experimental; mixed infection; Mutants; Mutation; N gene; NF-κB protein; nuclear localization signals; nucleocapsid; Nucleocapsids; Pathogens; phenotype; Phenotypes; Porcine reproductive and respiratory syndrome; Pork industry; Proteins; Respiratory diseases; Respiratory tract diseases; reverse genetics; Signal transduction; Swine; vaccines; Viral diseases; Viral infections; viral nonstructural proteins; Viremia; Virus diseases; Viruses; β-Interferon; United States
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1012128

Porcine reproductive and respiratory syndrome virus (PRRSV) is known to suppress the type I interferon (IFNs-α/β) response during infection. PRRSV also activates the NF-κB signaling pathway, leading to the production of proinflammatory cytokines during infection. In swine farms, co-infections of PRRSV and other secondary bacterial pathogens are common and exacerbate the production of proinflammatory cytokines, contributing to the porcine respiratory disease complex (PRDC) which is clinically a severe disease. Previous studies identified the non-structural protein 1β (nsp1β) of PRRSV-2 as an IFN antagonist and the nucleocapsid (N) protein as the NF-κB activator. Further studies showed the leucine at position 126 (L126) of nsp1β as the essential residue for IFN suppression and the region spanning the nuclear localization signal (NLS) of N as the NF-κB activation domain. In the present study, we generated a double-mutant PRRSV-2 that contained the L126A mutation in the nsp1β gene and the NLS mutation (ΔNLS) in the N gene using reverse genetics. The immunological phenotype of this mutant PRRSV-2 was examined in porcine alveolar macrophages (PAMs) in vitro and in young pigs in vivo. In PAMs, the double-mutant virus did not suppress IFN-β expression but decreased the NF-κB-dependent inflammatory cytokine productions compared to those for wild-type PRRSV-2. Co-infection of PAMs with the mutant PRRSV-2 and Streptococcus suis (S . suis) also reduced the production of NF-κB-directed inflammatory cytokines. To further examine the cytokine profiles and the disease severity by the mutant virus in natural host animals, 6 groups of pigs, 7 animals per group, were used for co-infection with the mutant PRRSV-2 and S . suis . The double-mutant PRRSV-2 was clinically attenuated, and the expressions of proinflammatory cytokines and chemokines were significantly reduced in pigs after bacterial co-infection. Compared to the wild-type PRRSV-2 and S . suis co-infection control, pigs coinfected with the double-mutant PRRSV-2 exhibited milder clinical signs, lower titers and shorter duration of viremia, and lower expression of proinflammatory cytokines. In conclusion, our study demonstrates that genetic modification of the type I IFN suppression and NF-κB activation functions of PRRSV-2 may allow us to design a novel vaccine candidate to alleviate the clinical severity of PRRS-2 and PRDC during bacterial co-infection.