Bats are important hosts for various zoonotic viral diseases. However, they rarely show signs of disease infection with such viruses. As the first line for virus control, the innate immune system of bats attracted our full attention. In this study, the Tadarida brasiliensis MDA5 gene (batMDA5), a major sensor for anti-RNA viral infection, was first cloned, and its biological functions in antiviral innate immunity were identified. Bioinformatics analysis shows that the amino acid sequence of batMDA5 is poorly conserved among species, and it is evolutionarily closer to humans. The mRNA of batMDA5 was significantly upregulated in Newcastle disease virus (NDV), avian influenza virus (AIV), and vesicular stomatitis virus (VSV)-infected bat TB 1 Lu cells. Overexpression of batMDA5 could activate IFNβ and inhibit vesicular stomatitis virus (VSV-GFP) replication in TB 1 Lu cells, while knockdown of batMDA5 yielded the opposite result. In addition, we found that the CARD domain was essential for MDA5 to activate IFNβ by constructing MDA5 domain mutant plasmids. These results indicated that bat employs a conserved MDA5 gene to trigger anti-RNA virus innate immune response. This study helps understand the biological role of MDA5 in innate immunity during evolution.
Reassortant variant viruses generated between 2009 H1N1 pandemic influenza virus [A(H1N1)pdm09] and endemic swine influenza viruses posed a potential risk to humans. Surprisingly, genetic analysis showed that almost all of these variant viruses contained the M segment from A(H1N1)pdm09, which originated from Eurasian avian-like swine influenza viruses. Studies have shown that the A(H1N1)pdm09 M gene is critical for the transmissibility and pathogenicity of the variant viruses. However, the M gene encodes two proteins, M1 and M2, and which of those plays a more important role in virus pathogenicity remains unknown. In this study, the M1 and M2 genes of A(H1N1)pdm09 were replaced with those of endemic H3N2 swine influenza virus, respectively. The chimeric viruses were rescued and evaluated in vitro and in mice. Both M1 and M2 of H3N2 affected the virus replication in vitro. In mice, the introduction of H3N2 M1 attenuated the chimeric virus, where all the mice survived from the infection, compared with the wild type virus that caused 100 % mortality. However, the chimeric virus containing H3N2 M2 was still virulent to mice, and caused 16.6% mortality, as well as similar body weight loss to the wild type virus infected group. Compared with the wild type virus, the chimeric virus containing H3N2 M1 induced lower levels of inflammatory cytokines and higher levels of anti-inflammatory cytokines, whereas the chimeric virus containing H3N2 M2 induced substantial pro-inflammatory responses, but higher levels of anti-inflammatory cytokines. The study demonstrated that Eurasian avian-like M1 played a more important role than M2 in the pathogenicity of A(H1N1)pdm09 in mice.
Staphylococcus aureus is the main pathogen that causes skin and skin structure infections and is able to survive and persist in keratinocytes of the epidermis. Since the evolution of multidrug-resistant bacteria, the use of phages and their lysins has presented a promising alternative approach to treatment. In this study, a cell wall hydrolase (also called lysin) derived from Staphylococcus phage JD007 (JDlys) was identified. JDlys showed strong lytic activity against methicillin-resistant Staphylococcus aureus (MRSA) strains from different sources and of different multilocus sequence typing (MLST) types. Furthermore, a fusion protein consisting of a cell-penetrating peptide derived from the trans-activating transcription (Tat) factor fused to JDlys (CPPTat-JDlys) was used to kill MRSA bacteria causing intracellular infections. CPPTat-JDlys, in which the fusion of CPPTat to JDlys had almost no effect on the bacteriolytic activity of JDlys, was able to effectively eliminate intracellular MRSA bacteria and alleviate the inflammatory response and cell damage caused by MRSA. Specifically, CPPTat-JDlys was able to combat MRSA-induced murine skin infections and, consequently, expedite the healing of cutaneous abscesses. These data suggest that the novel antimicrobial CPP-JDlys may be a worthwhile candidate as a treatment for skin and skin structure infections caused by MRSA.IMPORTANCES. aureus is the main cause of skin and skin structure infections due to its ability to invade and survive in the epithelial barrier. Due to the overuse of antibiotics in humans and animals, S. aureus has shown a high capacity for acquiring and accumulating mechanisms of resistance to antibiotics. Moreover, most antibiotics are usually limited in their ability to overcome the intracellular persistence of bacteria causing skin and skin structure infections. So, it is critical to seek a novel antimicrobial agent to eradicate intracellular S. aureus In this study, a cell-penetrating peptide fused to lysin (CPP-JDlys) was engineered. Our results show that CPP-JDlys can enter keratinocytes and effectively eliminate intracellular MRSA. Meanwhile, experiments with mice revealed that CPP-JDlys efficiently inhibits the proliferation of MRSA in murine skin and thus shortens the course of wound healing. Our results indicate that the CPP-fused lysin has potential for use for the treatment of skin infections caused by MRSA.
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