Bat Employs a Conserved MDA5 Gene to Trigger Antiviral Innate Immune Responses

A strain of Lactobacillus plantarum from piglet intestines enhances the anti-PoRV effect via the STING-IFN-I pathway

BACKGROUND

Rotavirus infection represents a major etiology of severe diarrheal disease in neonatal and weaned piglets, causing substantial economic burdens to the global swine industry. Lactobacillus plantarum, a ubiquitous probiotic in natural ecosystems, has demonstrated multifaceted biological functions. The stimulator of the interferon gene (STING) is involved in type I interferon (IFN-I) mediated host antiviral innate immunity, which is a pivotal adaptor in response to the microbial DNA/RNA-activated signaling pathways. Emerging evidence suggests that certain probiotic strains can activate the STING-dependent pathway to induce IFN-I responses. In the present study, we successfully isolated a strain of Lactobacillus plantarum (designated LP1)from porcine intestinal contents and investigate its potential to counteract porcine rotavirus (PoRV) infection via modulation of antiviral signaling pathway.

RESULT

LP1 exhibited superior tolerance to simulated gastrointestinal conditions (pH 3.0 and 0.3% bile salts) compared with other isolated Lactobacillus strains. In vitro adhesion assays demonstrated that LP1effectively colonized porcine intestinal epithelial cells (IPEC-J2) without inducing cytotoxicity or apoptosis. Animal experiments also confirmed the protective effect of LP1 in mice against rotavirus, by reducing body weight loss, promoting viral clearance in feces, and alleviating intestinal mucosal damage. Mechanistic investigations identified STING-IRF3 pathway activation as the pivotal antiviral mechanism. Both phosphorylation of STING and IRF3 in LP1-treated IPEC-J2 cells accompanied by upregulated transcription and secretion of IFN-β and interferon-stimulated genes (ISGs). Consistent findings were observed in intestinal tissues of LP1-protected mice with STING pathway activation correlating with reduction in viral titers. Crucially, STING inhibitor (C-170) administration could reverse LP1-mediated antiviral effects.

CONCLUSION

LP1 exerts potent anti-PoRV activity in both murine models and porcine intestinal epithelial (IPEC-J2) cells through STING-IRF3 signaling axis-mediated IFN-β production.

Conserved function of bat IRF7 in activating antiviral innate immunity: insights into the innate immune response in bats

Bats are natural hosts for various highly pathogenic viruses, which pose a considerable threat to humans and animals. However, they rarely display signs of disease infection from these viruses. The expression of IRF7-induced IFN-β plays a crucial role in preventing viral infections. However, the role of bat IRF7 during viral infection remains unclear. In this study, we cloned Tadarida brasiliensis IRF7 and discovered that its amino acid sequence was poorly conserved among species. Next, we investigated the expression of bat IRF7 mRNA in Tadarida brasiliensis lung cells (TB 1 Lu) infected with RNA viruses such as Newcastle disease virus (NDV), avian influenza virus (AIV), vesicular stomatitis virus (VSV), and the double-stranded RNA (dsRNA) analogue poly (I:C) and demonstrated that these viral infections significantly upregulated the mRNA expression of bat IRF7. Furthermore, the overexpression of IRF7 in TB1 Lu cells activated the expression of bat innate immune-related genes and inhibited virus replication. Importantly, we observed that bat IRF7 function is highly conserved in avian and mammalian species. Structurally, we revealed that the IRF domain of bat IRF7 is essential for activating IFN-β. In summary, our findings indicate that bat IRF7 has a conserved ability to activate bat antiviral innate immunity. This study provides a theoretical foundation for further understanding the innate immune response in bats.

Disease tolerance as immune defense strategy in bats: One size fits all?

Bats are natural reservoirs for zoonotic pathogens, yet the determinants of microbial persistence as well as the specific functionality of their immune system remain largely enigmatic. Their propensity to harbor viruses lethal to humans and/or livestock, mostly in absence of clinical disease, makes bats stand out among mammals. Defending against pathogens relies on avoidance, resistance, and/or tolerance strategies. In bats, disease tolerance has recently gained increasing attention as a prevailing host defense paradigm. We here summarize the current knowledge on immune responses in bats in the context of infection with zoonotic agents and discuss concepts related to disease tolerance. Acknowledging the wide diversity of bats, the broad spectrum of bat-associated microbial species, and immune-related knowledge gaps, we identify research priorities necessary to provide evidence-based proofs for disease tolerance in bats. Since disease tolerance relies on networks of biological processes, we emphasize that investigations beyond the immune system, using novel technologies and computational biology, could jointly advance our knowledge about mechanisms conferring bats reservoir abilities. Although disease tolerance may not be the "one fit all" defense strategy, deciphering disease tolerance in bats could translate into novel therapies and inform prevention of spillover infections to humans and livestock.

A tale of endurance: bats, viruses and immune dynamics

The emergence of highly zoonotic viral infections has propelled bat research forward. The viral outbreaks including Hendra virus, Nipah virus, Marburg virus, Ebola virus, Rabies virus, Middle East respiratory syndrome coronavirus, SARS-CoV and the latest SARS-CoV-2 have been epidemiologically linked to various bat species. Bats possess unique immunological characteristics that allow them to serve as a potential viral reservoir. Bats are also known to protect themselves against viruses and maintain their immunity. Therefore, there is a need for in-depth understanding into bat-virus biology to unravel the major factors contributing to the coexistence and spread of viruses.

Identification of pigeon mitochondrial antiviral signaling protein (MAVS) and its role in antiviral innate immunity

Pigeons can be infected with various RNA viruses, and their innate immune system responds to viral infection to establish an antiviral response. Mitochondrial antiviral signaling protein (MAVS), an important adaptor protein in signal transduction, plays a pivotal role in amplifying the innate immune response. In this study, we successfully cloned pigeon MAVS (piMAVS) and performed a bioinformatics analysis. The results showed that the caspase recruitment domain (CARD) and transmembrane (TM) domain are highly conserved in poultry and mammals but poorly conserved in other species. Furthermore, we observed that MAVS expression is upregulated both in pigeons and pigeon embryonic fibroblasts (PEFs) upon RNA virus infection. Overexpression of MAVS resulted in increased levels of β-interferon (IFN-β), IFN-stimulated genes (ISGs), and interleukin (ILs) mRNA and inhibited Newcastle disease virus (NDV) replication. We also found that piMAVS and human MAVS (huMAVS) induced stronger expression of IFN-β and ISGs when compared to chicken MAVS (chMAVS), and this phenomenon was also reflected in the degree of inhibition of NDV replication. Our findings demonstrate that piMAVS plays an important role in repressing viral replication by regulating the activation of the IFN signal pathway in pigeons. This study not only sheds light on the function of piMAVS in innate immunity but also contributes to a more comprehensive understanding of the innate immunity system in poultry. Our data also provide unique insights into the differences in innate immunity between poultry and mammal.

Genomic and biological variation in bat IFNs: An antiviral treatment approach

Bat-borne viruses have attracted considerable research, especially in relation to the Covid-19 pandemic. Although bats can carry multiple zoonotic viruses that are lethal to many mammalian species, they appear to be asymptomatic to viral infection despite the high viral loads contained in their bodies. There are several differences between bats and other mammals. One of the major differences between bats and other mammals is the bats' ability to fly, which is believed to have induced evolutionary changes. It may have also favoured them as suitable hosts for viruses. This is related to their tolerance to viral infection. Innate immunity is the first line of defence against viral infection, but bats have metamorphosed the type of responses induced by innate immunity factors such as interferons. The expression patterns of interferons differ, as do those of interferon-related genes such as interferon regulatory factors and interferon-stimulated genes that contribute to the antiviral response of infected cells. In addition, the signalling pathways related to viral infection and immune responses have been subject to evolutionary changes, including mutations compared to their homologues in other mammals and gene selection. This article discusses the differences in the interferon-mediated antiviral response in bats compared to that of other mammals and how these differences are correlated to viral tolerance in bats. The effect of bat interferons related genes on human antiviral response against bat-borne viruses is also discussed.

Antiviral effects of interferon-stimulated genes in bats

The interferon pathway is the first line of defense in viral infection in all mammals, and its induction stimulates broad expression of interferon-stimulated genes (ISGs). In mice and also humans, the antiviral function of ISGs has been extensively studied. As an important viral reservoir in nature, bats can coexist with a variety of pathogenic viruses without overt signs of disease, yet only limited data are available for the role of ISGs in bats. There are multiple species of bats and work has begun deciphering the differences and similarities between ISG function of human/mouse and different bat species. This review summarizes the current knowledge of conserved and bat-specific-ISGs and their known antiviral effector functions.