Comparison of the virulence of three H3N2 canine influenza virus isolates from Korea and China in mouse and Guinea pig models

Role of CIV NS1 Protein in Innate Immunity and Viral Replication

The innate immune pathway serves as the first line of defense against viral infections and plays a crucial role in the host's immune response in clearing viruses. Prior research has indicated that the influenza A virus has developed various strategies to avoid host immune responses. Nevertheless, the role of the NS1 protein of the canine influenza virus (CIV) in the innate immune pathway remains unclear. In this study, eukaryotic plasmids of NS1, NP, PA, PB1, and PB2 were constructed, and it was found that these proteins interact with melanoma differentiation-associated gene 5 (MDA5) and antagonize the activation of IFN-β promoters by MDA5. We selected the NS1 protein for further study and found that NS1 does not affect the interaction between the viral ribonucleoprotein (RNP) subunit and MDA5, but that it downregulates the expression of the laboratory of genetics and physiology 2 (LGP2) and retinoic acid-inducible gene-I (RIG-I) receptors in the RIG-I pathway. Additionally, NS1 was found to inhibit the expression of several antiviral proteins and cytokines, including MX dynamin like GTPase 1 (MX1), 2'-5'oligoadenylate synthetase (OAS), Signal Transducers and Activators of Transcription (STAT1), tripartite motif 25 (TRIM25), interleukin-2 (IL-2), IFN, IL-8, and IL-1β. To further investigate the role of NS1, a recombinant H3N2 virus strain (rH3N2) and an NS1-null virus (rH3N2ΔNS1) were rescued using reverse-genetic technology. The rH3N2ΔNS1 virus exhibited lower viral titers compared to rH3N2, but had a stronger activation effect on the receptors LGP2 and RIG-I. Furthermore, when compared to rH3N2, rH3N2ΔNS1 exhibited a more pronounced activation of antiviral proteins such as MX1, OAS, STAT1, and TRIM25, as well as antiviral cytokines such as IL-6, IFN-β, and IL-1β. These findings suggest a new mechanism by which NS1, a nonstructural protein of CIV, facilitates innate immune signaling and provides new avenues for the development of antiviral strategies.

Correlation of adhesion molecules and non-typeable haemophilus influenzae growth in a mice coinfected model of acute inflammation

Primary influenza virus (IV) infection can predispose hosts to secondary infection with Haemophilus influenzae (H. influenzae), which further increases the severity and mortality of the disease. While adhesion molecules play a key role in the host inflammatory response and H. influenzae colonization, it remains to be clarified which types of adhesion molecules are associated with H. influenzae colonization and invasion following IV infection. In this study, we established a mouse model of co-infection with influenza A virus (A/Puerto Rico/8/34, H1N1) (PR8) and non-typeable H. influenzae (NTHi) and found that sequential infection with PR8 and NTHi induced a lethal synergy in mice. This outcome may be possibly due to increased NTHi loads, greater lung damage and higher levels of cytokines. Furthermore, the protein levels of intracellular adhesion molecules-1 (ICAM-1) and Fibronectin (Fn) were significantly increased in the lungs of coinfected mice, but the levels of carcinoembryonic adhesion molecule (CEACAM)-1, CEACAM-5 and platelet-activating factor receptor (PAFr) were unaffected. Both the protein levels of ICAM-1 and Fn were positively correlated with NTHi growth. These results indicate the correlation between adhesion molecules, including ICAM-1 and Fn, and NTHi growth in secondary NTHi pneumonia following primary IV infection.

Establishment of a model of Mycoplasma hyopneumoniae infection using Bama miniature pigs

Mycoplasma hyopneumoniae (M. hyopneumoniae), is the primary aetiological agent of enzootic pneumonia leading to chronic respiratory disease prevalent worldwide. Conventional pigs are the only animals used for pathogenicity studies and vaccine evaluations of M. hyopneumoniae. Considering that the challenge animals have better genetic stability and a smaller body size to operate with, an alternative experimental animal model of M. hyopneumoniae infection with Bama miniature pigs was established. Nine seven-week-old snatch-farrowed, porcine colostrum-deprived (SF-pCD) Bama miniature pigs and nine conventional pigs were randomly divided into two infected groups (Bama miniature-infected (BI) and conventional-infected groups (CI), BI and CI, n = 6) and two control groups (Bama miniature control (BC) and conventional control (CC) groups, BC and CC, n = 3). Every piglet was tracheally inoculated with 5 × 108 CCU/mL containing 10% suspension of a stock of frozen lung homogenate from SF-pCD pigs infected with virulent strain JS or sterilized KM2 medium. Typical lung lesions appeared in all infected pigs after necropsy, and the mean gross lung lesions was 17.3 and 13.7 in groups of BI and CI. Serum IgG and nasal sIgA antibody titres were increased significantly. Cilia shedding and mucus staining increased greatly in JS-infected bronchi. Obvious reddish gross lesions and M. hyopneumoniae antigen were detected, especially apparently observed in group of BI. Moreover, DNA copies of M. hyopneumoniae from bronchoalveolar lavage fluid (BALF) of each JS-infected piglet reached more than 108, and M. hyopneumoniae could be re-isolated from each infected BALF. These results indicate that Bama miniature pigs could be used as an alternative and more maneuverable experimental infection model for M. hyopneumoniae and display typical clinical and pathological features consistent with those in conventional pigs.

Role of CARD Region of MDA5 Gene in Canine Influenza Virus Infection

MDA5 belongs to the RIG-I-like receptor family, which is involved in innate immunity. During viral infection, MDA5 generates an antiviral response by recognizing the ligand to activate interferon. However, the role and mechanism of MDA5 in canine influenza virus (CIV) infection are unclear. To understand the mechanism of canine MDA5-mediated innate immunity during CIV infection, we detected the distribution of MDA5 in beagles, and the structural prediction showed that MDA5 was mainly composed of a CARD domain, RD domain, and DExD/H helix structure. Moreover, we found that MDA5 inhibits CIV replication. Furthermore, in the dual luciferase assay, we revealed that the CARD region of MDA5 strongly activated the IFN-β promoter and mainly transmitted signals through the CARD region. Overexpression of the CARD region of MDA5 revealed that the MDA5-mediated signaling pathway could transmit signals by activating the IRF3/NF-κB and IRF3 promoters, promoting the expression of antiviral proteins and cytokine release, thereby inhibiting CIV replication. Upon silencing of MDA5, cytokine production decreased, while the replication ability of CIV was increased. Thus, this study revealed a novel mechanism by which MDA5 mediated CIV infection and provided new avenues for the development of antiviral strategies.

Morphological features and pathogenicity of mutated canine influenza viruses from China and South Korea

The canine influenza virus (CIV) has spread globally from East Asia to the United States and mutated and evolved to generate various CIVs. Since 2010, the mutant CIVs found in China and Korea have presented increased virulence in mice, guinea pigs and ferrets, which has raised concerns about public health and outbreak of a severe canine flu. We analysed and compared the morphology, cellular uptake and pathogenicity of CIV variants in host animals, to determine their characteristics. The Chinese mutant, A/canine/Jiangsu/06/2010[H3N2](JS10), has two amino acid insertions at the distal end of the NA stalk, and A/canine/Korea/01/2007[H3N2](KR07) presented comparable efficiency of cell uptake and a similar morphology to spherical or small ovoid particles. However, KR07M generated from swapping of M segment of the pandemic isolate, A/California/04/2009 [H1N1] (CA04) into KR07 alone accounted for morphologic change and higher efficiency of cell uptake to the wild-type CIV. This study will provide an insight into the pathogenesis, transmission and evolution of CIVs and help determine future countermeasures.