NLRP3 inflammasome activation by Foot-and-mouth disease virus infection mainly induced by viral RNA and non-structural protein 2B

Lyssavirus matrix protein inhibits NLRP3 inflammasome assembly by binding to NLRP3

Lyssavirus is a kind of neurotropic pathogen that needs to evade peripheral host immunity to enter the central nervous system to accomplish infection. NLRP3 inflammasome activation is essential for the host to defend against pathogen invasion. This study demonstrates that the matrix protein (M) of lyssavirus can inhibit both the priming step and the activation step of NLRP3 inflammasome activation. Specifically, M of lyssavirus can compete with NEK7 for binding to NLRP3, which restricts downstream apoptosis-associated speck-like protein containing a CARD (ASC) oligomerization. The serine amino acid at the 158th site of M among lyssavirus is critical for restricting ASC oligomerization. Moreover, recombinant lab-attenuated lyssavirus rabies (rabies lyssavirus [RABV]) with G158S mutation at M decreases interleukin-1β (IL-1β) production in bone-marrow-derived dendritic cells (BMDCs) to facilitate lyssavirus invasion into the brain thereby elevating pathogenicity in mice. Taken together, this study reveals a common mechanism by which lyssavirus inhibits NLRP3 inflammasome activation to evade host defenses.

The Ca2+-dependent phosphatase calcineurin dephosphorylates TBK1 to suppress antiviral innate immunity

Tumor necrosis factor receptor-associated factor family member-associated NF-κB activator-binding kinase 1 (TBK1) plays a key role in the induction of the type 1 interferon (IFN-I) response, which is an important component of innate antiviral defense. Viruses target calcium (Ca2+) signaling networks, which participate in the regulation of the viral life cycle, as well as mediate the host antiviral response. Although many studies have focused on the role of Ca2+ signaling in the regulation of IFN-I, the relationship between Ca2+ and TBK1 in different infection models requires further elucidation. Here, we examined the effects of the Newcastle disease virus (NDV)-induced increase in intracellular Ca2+ levels on the suppression of host antiviral responses. We demonstrated that intracellular Ca2+ increased significantly during NDV infection, leading to impaired IFN-I production and antiviral immunity through the activation of calcineurin (CaN). Depletion of Ca²+ was found to lead to a significant increase in virus-induced IFN-I production resulting in the inhibition of viral replication. Mechanistically, the accumulation of Ca2+ in response to viral infection increases the phosphatase activity of CaN, which in turn dephosphorylates and inactivates TBK1 in a Ca2+-dependent manner. Furthermore, the inhibition of CaN on viral replication was counteracted in TBK1 knockout cells. Together, our data demonstrate that NDV hijacks Ca2+ signaling networks to negatively regulate innate immunity via the CaN-TBK1 signaling axis. Thus, our findings not only identify the mechanism by which viruses exploit Ca2+ signaling to evade the host antiviral response but also, more importantly, highlight the potential role of Ca2+ homeostasis in the viral innate immune response.IMPORTANCEViral infections disrupt intracellular Ca2+ homeostasis, which affects the regulation of various host processes to create conditions that are conducive for their own proliferation, including the host immune response. The mechanism by which viruses trigger TBK1 activation and IFN-I induction through viral pathogen-associated molecular patterns has been well defined. However, the effects of virus-mediated Ca2+ imbalance on the IFN-I pathway requires further elucidation, especially with respect to TBK1 activation. Herein, we report that NDV infection causes an increase in intracellular free Ca2+ that leads to activation of the serine/threonine phosphatase CaN, which subsequently dephosphorylates TBK1 and negatively regulates IFN-I production. Furthermore, depletion of Ca2+ or inhibition of CaN activity exerts antiviral effects by promoting the production of IFN-I and inhibiting viral replication. Thus, our results reveal the potential role of Ca2+ in the innate immune response to viruses and provide a theoretical reference for the treatment of viral infectious diseases.

Inflammatory Consequences: Hepatitis C Virus-Induced Inflammasome Activation and Pyroptosis

Hepatitis C virus (HCV), despite the availability of effective direct-acting antivirals (DAAs) that clear the virus from >95% of individuals treated, continues to cause significant health care burden due to disease progression that can lead to fibrosis, cirrhosis, and/or hepatocellular carcinoma. The fact that some people who are treated with DAAs still go on to develop worsening liver disease warrants further study into the immunopathogenesis of HCV. Many viral infections, including HCV, have been associated with activation of the inflammasome/pyroptosis pathway. This inflammatory cell death pathway ultimately results in cell lysis and release of inflammatory cytokines, IL-18 and IL-1β. This review will report on studies that investigated HCV and inflammasome activation/pyroptosis. This includes clinical in vivo data showing elevated pyroptosis-associated cytokines in the blood of individuals living with HCV, studies of genetic associations of pyroptosis-related genes and development of liver disease, and in vitro studies aimed at understanding the mechanism of pyroptosis induced by HCV. Finally, we discuss major gaps in understanding and outstanding questions that remain in the field of HCV-induced pyroptosis.

Effects of enzymatically hydrolyzed yeast supplementation on blood attributes, antioxidant status and gene expression of cytokines in vaccinated dairy cows

This study was done to assess the effects of hydrolyzed yeast on blood cells counts, antioxidant status and gene expression of pro-inflammatory and anti-inflammatory cytokines of vaccinated dairy cows. Twenty Holstein lactating dairy cows were randomly divided into four groups received basal diet without (control) and with 10, 20 and 30 g/d/head of hydrolyzed yeast. Cows were vaccinated against foot and mouth disease virus at day 10 and blood samples were taken 10 days after. Cows received hydrolyzed yeast at doses of 20 and 30 g/d/head had the lowest and those in the control group had the highest malondialdehyde concentration. Cows received hydrolyzed yeast at dose of 20 g/d/head had the highest lymphocyte and the lowest neutrophil/lymphocyte ratio. IL-1β and TNF-α downregulated and INF-γ up-regulated in cows received different doses of hydrolyzed yeast. The lowest expression of IL-1β and TNF-α and the highest expression of INF-γ was for cows received hydrolyzed yeast at dose of 20 g/d/head. The highest titers against foot and mouth disease virus were for cows received hydrolyzed yeast at dose of 20 g/d/head and the lowest titer was for the control group. Supplementation of 20 g/d/head hydrolyzed yeast recommended in vaccinated cows.

Autophagy and Inflammation: Regulatory Roles in Viral Infections

Autophagy is a highly conserved intracellular degradation pathway in eukaryotic organisms, playing an adaptive role in various pathophysiological processes throughout evolution. Inflammation is the immune system's response to external stimuli and tissue damage. However, persistent inflammatory reactions can lead to a range of inflammatory diseases and cancers. The interaction between autophagy and inflammation is particularly evident during viral infections. As a crucial regulator of inflammation, autophagy can either promote or inhibit the occurrence of inflammatory responses. In turn, inflammation can establish negative feedback loops by modulating autophagy to suppress excessive inflammatory reactions. This interaction is pivotal in the pathogenesis of viral diseases. Therefore, elucidating the regulatory roles of autophagy and inflammation in viral infections will significantly enhance our understanding of the mechanisms underlying related diseases. Furthermore, it will provide new insights and theoretical foundations for disease prevention, treatment, and drug development.

PRRSV inhibited the proliferation of CSFV by inducing IL-1β maturation via NLRP3 inflammasome activation

PRRSV and CSFV are both common infectious pathogens in porcine populations, posing significant threats to the healthy development of the porcine industry. Vaccine immunization is the main way to prevent and control these two diseases. Increasing studies have demonstrated that there is an interaction between PRRSV co-infection and CSFV vaccine immune failure. To investigate the effect of PRRSV infection on CSFV proliferation and its molecular mechanism, the proliferation dynamics of PRRSV/CSFV, the NLRP3 inflammasome components, and IL-1β expression levels were detected in PRRSV/CSFV alone- or co-infection. Subsequently, the relationship between inflammasome activation, IL-1β expression, and CSFV proliferation was analyzed through the construction of an inflammasome activation model, specific siRNA interference, and specific inhibitor treatment. The results showed that CSFV infection had a poor regulatory effect on NLRP3 inflammasome activation and IL-1β maturation, but PRRSV and CSFV co-infection could significantly up-regulate the expression of NLRP3 and ASC, induce Caspase-1 activation, and promote IL-1β maturation. It was further determined that NLRP3 inflammasome components played important roles in IL-1β maturation and inhibiting CSFV proliferation by PRRSV. Additional experiments indicated that PRRSV replication is essential for NLRP3 inflammasome activation, IL-1β maturation, and CSFV proliferation inhibition. More importantly, NLRP3 inflammasome activation is regulated by the TLR4-MyD88-NF-κB pathways. In conclusion, PRRSV infection induced IL-1β maturation by activating the NLRP3 inflammasome through the TLR4-MyD88-NF-κB pathways and then inhibited the proliferation of CSFV. These data further improved the theoretical basis for PRRSV inducing inflammatory factors and leading to the failure of CSFV immunization.

The NLRP3 inflammasome in viral infection (Review)

The interplay between pathogen and host determines the immune response during viral infection. The Nod‑like receptor (NLR) protein 3 inflammasome is a multiprotein complex that induces the activation of inflammatory caspases and the release of IL‑1β, which play an important role in the innate immune responses. In the present review, the mechanisms of the NLR family pyrin domain containing 3 inflammasome activation and its dysregulation in viral infection were addressed.

Foot-and-mouth disease virus downregulates vacuolar protein sorting 28 to promote viral replication

Vacuolar protein sorting 28 (Vps28), a component of the ESCRT-I (endosomal sorting complex required for transport I), plays an important role in the pathogen life cycle. Here, we investigated the reciprocal regulation between Vps28 and the foot-and-mouth disease virus (FMDV). Overexpression of Vps28 decreased FMDV replication. On the contrary, the knockdown of Vps28 increased viral replication. Subsequently, the mechanistic study showed that Vps28 destabilized the replication complex (RC) by associating with 3A rather than 2C protein. In addition, Vps28 targeted FMDV VP0, VP1, and VP3 for degradation to inhibit viral replication. To counteract this, FMDV utilized tactics to restrict Vps28 to promote viral replication. FMDV degraded Vps28 mainly through the ubiquitin-proteasome pathway. Additional data demonstrated that 2B and 3A proteins recruited E3 ubiquitin ligase tripartite motif-containing protein 21 to degrade Vps28 at Lys58 and Lys25, respectively, and FMDV 3Cpro degraded Vps28 through autophagy and its protease activity. Meantime, the 3Cpro-mediated Vps28 degradation principally alleviated the ability to inhibit viral propagation. Intriguingly, we also demonstrated that the N-terminal and C-terminal domains of Vps28 were responsible for the suppression of FMDV replication, which suggested the elaborated counteraction between FMDV and Vps28. Collectively, our results first investigate the role of ESCRTs in host defense against picornavirus and unveil underlying strategies utilized by FMDV to evade degradation machinery for triumphant propagation. IMPORTANCE ESCRT machinery plays positive roles in virus entry, replication, and budding. However, little has been reported on its negative regulation effects during viral infection. Here, we uncovered the novel roles of ESCRT-I subunit Vps28 on FMDV replication. The data indicated that Vps28 destabilized the RC and impaired viral structural proteins VP0, VP1, and VP3 to inhibit viral replication. To counteract this, FMDV hijacked intracellular protein degradation pathways to downregulate Vps28 expression and thus promoted viral replication. Our findings provide insights into how ESCRT regulates pathogen life cycles and elucidate additional information regarding FMDV counteraction of host antiviral activity.

Inflammasome activation by viral infection: mechanisms of activation and regulation

Viral diseases are the most common problems threatening human health, livestock, and poultry industries worldwide. Viral infection is a complex and competitive dynamic biological process between a virus and a host/target cell. During viral infection, inflammasomes play important roles in the host and confer defense mechanisms against the virus. Inflammasomes are polymeric protein complexes and are considered important components of the innate immune system. These immune factors recognize the signals of cell damage or pathogenic microbial infection after activation by the canonical pathway or non-canonical pathway and transmit signals to the immune system to initiate the inflammatory responses. However, some viruses inhibit the activation of the inflammasomes in order to replicate and proliferate in the host. In recent years, the role of inflammasome activation and/or inhibition during viral infection has been increasingly recognized. Therefore, in this review, we describe the biological properties of the inflammasome associated with viral infection, discuss the potential mechanisms that activate and/or inhibit NLRP1, NLRP3, and AIM2 inflammasomes by different viruses, and summarize the reciprocal regulatory effects of viral infection on the NLRP3 inflammasome in order to explore the relationship between viral infection and inflammasomes. This review will pave the way for future studies on the activation mechanisms of inflammasomes and provide novel insights for the development of antiviral therapies.

NLRP3 Inflammasome Involved with Viral Replication in Cytopathic NADL BVDV Infection and IFI16 Inflammasome Connected with IL-1β Release in Non-Cytopathic NY-1 BVDV Infection in Bovine Macrophages

Inflammasomes are multiprotein complexes that play a role in the processing of proinflammatory cytokines such as interleukin 1 beta (IL-1β). The secretion of IL-1β in bovine macrophages infected with the bovine viral diarrhea virus (BVDV) cytopathic strain NADL (NADLcp-BVDV) is caspase 1-dependent. In the present study, we found that in macrophages infected with NADL, the NLRP3 inflammasome participated in the maturation of IL-1β as the level decreased from 4629.3 pg/mL to 897.0 pg/mL after treatment with cytokine release inhibitory drug 3 (CRID3). Furthermore, NLRP3 activation has implications regarding viral replication, as there was a decrease in the viral titer until 1 log of a supernatant of macrophages that were inhibited with CRID3 remained. In the case of the non-cytopathic BVDV strain NY-1 (NY-1 ncpBVDV), IL-1β secretion is not affected by NLRP3, but could be related to the IFI16 inflammasome; we found a colocalization of IFI16 with ASC using confocal microscopy in infected macrophages with the NY-1 ncp-BVDV biotype. To relate IFI16 activation to IL-1β release, we used ODN TTAGGG (A151), a competitive inhibitor of IFI16; the results show a decrease in its level from 248 pg/mL to 128.3 pg/mL. Additionally, we evaluated the caspase 1 activation downstream of IFI16 and found a decrease in the IL-1β from 252.9 pg/mL to 63.5 pg/mL when caspase 1 was inhibited with Y-VAD. Our results provide an improved understanding of the mechanisms involved in the viral replication, inflammation and pathogenesis of bovine viral diarrhea.

Targeting Inflammasome Activation in Viral Infection: A Therapeutic Solution?

Inflammasome activation is exclusively involved in sensing activation of innate immunity and inflammatory response during viral infection. Accumulating evidence suggests that the manipulation of inflammasome assembly or its interaction with viral proteins are critical factors in viral pathogenesis. Results from pilot clinical trials show encouraging results of NLRP3 inflammasome suppression in reducing mortality and morbidity in SARS-CoV-2-infected patients. In this article, we summarize the up-to-date understanding of inflammasomes, including NLRP3, AIM2, NLRP1, NLRP6, and NLRC4 in various viral infections, with particular focus on RNA viruses such as SARS-CoV-2, HIV, IAV, and Zika virus and DNA viruses such as herpes simplex virus 1. We also discuss the current achievement of the mechanisms involved in viral infection-induced inflammatory response, host defense, and possible therapeutic solutions.

Uncoupled pyroptosis and IL-1β secretion downstream of inflammasome signaling

Inflammasomes are supramolecular platforms that organize in response to various damage-associated molecular patterns and pathogen-associated molecular patterns. Upon activation, inflammasome sensors (with or without the help of ASC) activate caspase-1 and other inflammatory caspases that cleave gasdermin D and pro-IL-1β/pro-IL-18, leading to pyroptosis and mature cytokine secretion. Pyroptosis enables intracellular pathogen niche disruption and intracellular content release at the cost of cell death, inducing pro-inflammatory responses in the neighboring cells. IL-1β is a potent pro-inflammatory regulator for neutrophil recruitment, macrophage activation, and T-cell expansion. Thus, pyroptosis and cytokine secretion are the two main mechanisms that occur downstream of inflammasome signaling; they maintain homeostasis, drive the innate immune response, and shape adaptive immunity. This review aims to discuss the possible mechanisms, timing, consequences, and significance of the two uncoupling preferences downstream of inflammasome signaling. While pyroptosis and cytokine secretion may be usually coupled, pyroptosis-predominant and cytokine-predominant uncoupling are also observed in a stimulus-, cell type-, or context-dependent manner, contributing to the pathogenesis and development of numerous pathological conditions such as cryopyrin-associated periodic syndromes, LPS-induced sepsis, and Salmonella enterica serovar Typhimurium infection. Hyperactive cells consistently release IL-1β without LDH leakage and pyroptotic death, thereby leading to prolonged inflammation, expanding the lifespans of pyroptosis-resistant neutrophils, and hyperactivating stimuli-challenged macrophages, dendritic cells, monocytes, and specific nonimmune cells. Death inflammasome activation also induces GSDMD-mediated pyroptosis with no IL-1β secretion, which may increase lethality in vivo. The sublytic GSDMD pore formation associated with lower expressions of pyroptotic components, GSDMD-mediated extracellular vesicles, or other GSDMD-independent pathways that involve unconventional secretion could contribute to the cytokine-predominant uncoupling; the regulation of caspase-1 dynamics, which may generate various active species with different activities in terms of GSDMD or pro-IL-1β, could lead to pyroptosis-predominant uncoupling. These uncoupling preferences enable precise reactions to different stimuli of different intensities under specific conditions at the single-cell level, promoting cooperative cell and host fate decisions and participating in the pathogen "game". Appropriate decisions in terms of coupling and uncoupling are required to heal tissues and eliminate threats, and further studies exploring the inflammasome tilt toward pyroptosis or cytokine secretion may be helpful.

EV-A71 induced IL-1β production in THP-1 macrophages is dependent on NLRP3, RIG-I, and TLR3

Enterovirus A71 (EV-A71) is an emerging enterovirus that can cause neurological complications. Enhanced serum IL-1β levels were observed in EV-A71 patients with severe neurological symptoms. However, the roles of sensors in enterovirus-induced IL-1β production are unclear. In this study, we identified that pattern recognition receptors, including RIG-I, TLR3, and TLR8, are implicated in EV-A71-triggered IL-1β release in human macrophages. EV-A71 infection results in caspase-1 and caspase-8, which act as regulators of EV-A71-induced NLRP3 and RIG-I inflammasome activation. Moreover, knockdown of the expression of TLR3 and TLR8 decreased the released IL-1β in an NLRP3-dependent manner. Since TLR3 and TLR8 ligands promote NLRP3 inflammasome activation via caspase-8, the alternative pathway may be involved. In summary, these results indicate that activation of the NLRP3 and RIG-I inflammasomes in EV-A71-infected macrophages is mediated by caspase-1 and caspase-8 and affected by TLRs, including TLR3 and TLR8.

Foot-and-mouth disease virus non-structural protein 2B downregulates the RLR signaling pathway via degradation of RIG-I and MDA5

Foot-and-mouth disease virus (FMDV) is a single-stranded, positive-sense RNA virus containing at least 13 proteins. Many of these proteins show immune modulation capabilities. As a non-structural protein of the FMDV, 2B is involved in the rearrangement of the host cell membranes and the disruption of the host secretory pathway as a viroporin. Previous studies have also shown that FMDV 2B plays a role in the modulation of host type-I interferon (IFN) responses through the inhibition of expression of RIG-I and MDA5, key cytosolic sensors of the type-I IFN signaling. However, the exact molecular mechanism is poorly understood. Here, we demonstrated that FMDV 2B modulates host IFN signal pathway by the degradation of RIG-I and MDA5. FMDV 2B targeted the RIG-I for ubiquitination and proteasomal degradation by recruiting E3 ubiquitin ligase ring finger protein 125 (RNF125) and also targeted MDA5 for apoptosis-induced caspase-3- and caspase-8-dependent degradation. Ultimately, FMDV 2B significantly inhibited RNA virus-induced IFN-β production. Importantly, we identified that the C-terminal amino acids 126-154 of FMDV 2B are essential for 2B-mediated degradation of the RIG-I and MDA5. Collectively, these results provide a clearer understanding of the specific molecular mechanisms used by FMDV 2B to inhibit the IFN responses and a rational approach to virus attenuation for future vaccine development.

NLRP3 inflammasome activation mechanism and its role in autoimmune liver disease

The NLRP3 inflammasome is a multiprotein binding compound comprising NLRP3, connector protein ASC, and effector protein pro-caspase-1. When the NLRP3 inflammasome senses a danger signal from the host or pathogen, activated caspase-1 cleaves the precursors of interleukin (IL)-1β and IL-18 into mature proinflammatory cytokines, simultaneously causing lysis via the pore-forming protein gasdermin D. This induction of cell inflammatory pyroptosis suggests that it is a key process in the innate immune response to pathogens or cellular stress. Recent studies have shown that NLRP3 inflammasome also plays an important role in regulating autoimmune liver diseases, including autoimmune hepatitis, primary biliary cholangitis, and primary sclerosclerotic cholangitis. In this review, we summarize the structure, activation and modulation of the NLRP3 inflammasome, highlight the progress in research on the role of NLRP3 inflammasome in the occurrence and development of autoimmune liver diseases, and discuss potential strategies for targeting the NLRP3 inflammasome in the treatment of autoimmune liver diseases.

Heat Shock Protein 60 Is Involved in Viral Replication Complex Formation and Facilitates Foot and Mouth Virus Replication by Stabilizing Viral Nonstructural Proteins 3A and 2C

The maintenance of viral protein homeostasis depends on the machinery of the infected host cells, giving us an insight into the interplay between host and virus. Accumulating evidence suggests that heat shock protein 60 (HSP60), as one molecular chaperone, is involved in regulating virus infection. However, the role of HSP60 during foot-and-mouth disease virus (FMDV) replication and its specific mechanisms have not been reported. We demonstrate that HSP60 modulates the FMDV life cycle. HSP60 plays a role at the postentry stage of the viral life cycle, including RNA replication and mRNA translation; however, HSP60 does not affect viral replication of Seneca Valley virus (SVA) or encephalomyocarditis virus (EMCV). We found that HSP60 is involved in FMDV replication complex (RC) formation. Furthermore, our results indicate that HSP60 interacts with FMDV nonstructural proteins 3A and 2C, key elements of the viral replication complex. We also show that HSP60 regulates the stability of 3A and 2C via caspase-dependent and autophagy-lysosome-dependent degradation, thereby promoting FMDV RNA synthesis and mRNA translation mediated by the RC. Additionally, we determined that the apical domain of HSP60 is responsible for interacting with 3A and 2C. The N terminus of 3A and ATPase domain of 2C are involved in binding to HSP60. Importantly, HSP60 depletion potently reduced FMDV pathogenicity in infected mice. Altogether, this study demonstrates a specific role of HSP60 in promoting FMDV replication. Furthermore, targeting host HSP60 will help us design the FMDV-specific antiviral drugs.

Echovirus 11 infection induces pyroptotic cell death by facilitating NLRP3 inflammasome activation

Echovirus 11 (ECHO 11) is a positive-strand RNA virus belonging to the genus Enterovirus of the family Picornaviridae. ECHO 11 infections can cause severe inflammatory illnesses in neonates, including severe acute hepatitis with coagulopathy. The activation of NLRP3 inflammasome is important for host defense against invading viruses, which also contributes to viral pathogenicity. However, whether and how ECHO 11 induces NLRP3 inflammasome activation remains unclear. In this study, we isolated a clinical strain of ECHO 11 from stools of an ECHO 11-infected newborn patient with necrotizing hepatitis. This virus shared 99.95% sequence identity with the previously published ECHO 11 sequence. The clinically isolated ECHO 11 can efficiently infect liver cells and strongly induces inflammation. Moreover, we showed that ECHO 11 induced IL-1β secretion and pyroptosis in cells and mouse bone marrow-derived macrophages (BMDMs). Furthermore, ECHO 11 infection triggered NLRP3 inflammasome activation, as evidenced by cleavages of GSDMD, pro-IL-1β and pro-caspase-1, and the release of LDH. ECHO 11 2B protein was required for NLRP3 inflammasome activation via interacting with NLRP3 to facilitate the inflammasome complex assembly. In vivo, expression of ECHO 11 2B also activated NLRP3 inflammasome in the murine liver. Besides, 2Bs of multiple EVs can also interact with NLRP3 and induce NLRP3 inflammasome activation. Together, our findings demonstrate a mechanism by which ECHO 11 induces inflammatory responses by activating NLRP3 inflammasome, providing novel insights into the pathogenesis of ECHO 11 infection.

NLRP3 inflammasome is important for host defense against invading viruses, and contributes to viral pathogenicity. Human echovirus 11 (ECHO 11) belongs to the Enterovirus genus from the family Picornavirida, and it can cause severe acute hepatitis in newborns with high morbidity and mortality. However, the knowledge about the pathogenesis of ECHO 11 infection is limited. Whether and how ECHO 11 induces NLRP3 inflammasome activation remains unclear. This work provides the first demonstration that ECHO 11 can induce inflammatory responses via activating NLRP3 inflammasome and pyroptosis. More importantly, ECHO 11-encoded 2B protein was found to activate NLRP3 inflammasome in cells and in vivo, and the interaction between 2B and NLRP3 was required for inflammasome complex assembly. Furthermore, we uncovered that 2Bs of other enteroviruses, including enterovirus 71, coxsackievirus A16 (CVA16) and CVB3 could induce NLRP3 inflammasome and interact with NLRP3. Our findings uncover a mechanism by which ECHO 11 induces inflammatory responses and demonstrate a novel function of ECHO 11 2B.

Calcium Ions Signaling: Targets for Attack and Utilization by Viruses

Calcium, as a second intracellular messenger, participate in various physiological and biochemical processes, including cell growth and proliferation, energy metabolism, information transfer, cell death, and immune response. Ca2+ channels or pumps in plasma and organelle membranes and Ca2+-related proteins maintain Ca2+ homeostasis by regulating Ca2+ inflow, outflow and buffering to avoid any adverse effects caused by Ca2+ overload or depletion. Thus, Ca2+ signaling also provides a target for virus invasion, replication, proliferation and release. After hijacking the host cell, viruses exploit Ca2+ signaling to regulate apoptosis and resist host immunity to establish persistent infection. In this review, we discuss cellular Ca2+ signaling and channels, interaction of calcium-associated proteins with viruses, and host cell fate, as well as the role of Ca2+ in cell death and antiviral response during viral infection.

PRRSV Infection Induces Gasdermin D-Driven Pyroptosis of Porcine Alveolar Macrophages through NLRP3 Inflammasome Activation

For more than 3 decades, mounting evidence has associated porcine reproductive and respiratory syndrome virus (PRRSV) infection with late-term abortions and stillbirths in sows and respiratory disease in piglets, causing enormous economic losses to the global swine industry. However, to date, the underlying mechanisms of PRRSV-triggered cell death have not been well clarified, especially in the pulmonary inflammatory injury characterized by the massive release of pro-inflammatory factors. Here, we demonstrated that PRRSV infection triggered gasdermin D-mediated host pyroptosis in vitro and in vivo. Mechanistically, PRRSV infection triggered disassembly of the trans-Golgi network (TGN); the dispersed TGN then acted as a scaffold for NLRP3 activation through phosphatidylinositol-4-phosphate. In addition, PRRSV replication-transcription complex (RTC) formation stimulated TGN dispersion and pyroptotic cell death. Furthermore, our results indicated that TMEM41B, an endoplasmic reticulum (ER)-resident host protein, functioned as a crucial host factor in the formation of PRRSV RTC, which is surrounded by the intermediate filament network. Collectively, these findings uncover new insights into clinical features as previously unrecognized mechanisms for PRRSV-induced pathological effects, which may be conducive to providing treatment options for PRRSV-associated diseases and may be conserved during infection by other highly pathogenic viruses. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the pathogens responsible for major economic losses in the global swine industry. Characterizing the detailed process by which PRRSV induces cell death pathways will help us better understand viral pathogenesis and provide implications for therapeutic intervention against PRRSV. Here, we showed that PRRSV infection induces GSDMD-driven host pyroptosis and IL-1β secretion through NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation in vitro and in vivo. Furthermore, the molecular mechanisms of PRRSV-induced NLRP3 inflammasome activation and pyroptosis are elucidated here. The dispersed trans-Golgi network (TGN) induced by PRRSV serves as a scaffold for NLRP3 aggregation into multiple puncta via phosphatidylinositol 4-phosphate (PtdIns4P). Moreover, the formation of PRRSV replication-transcription complex is essential for TGN dispersion and host pyroptosis. This research advances our understanding of the PRRSV-mediated inflammatory response and cell death pathways, paving the way for the development of effective treatments for PRRSV diseases.

Functions of Viroporins in the Viral Life Cycle and Their Regulation of Host Cell Responses

Viroporins are virally encoded transmembrane proteins that are essential for viral pathogenicity and can participate in various stages of the viral life cycle, thereby promoting viral proliferation. Viroporins have multifaceted effects on host cell biological functions, including altering cell membrane permeability, triggering inflammasome formation, inducing apoptosis and autophagy, and evading immune responses, thereby ensuring that the virus completes its life cycle. Viroporins are also virulence factors, and their complete or partial deletion often reduces virion release and reduces viral pathogenicity, highlighting the important role of these proteins in the viral life cycle. Thus, viroporins represent a common drug-protein target for inhibiting drugs and the development of antiviral therapies. This article reviews current studies on the functions of viroporins in the viral life cycle and their regulation of host cell responses, with the aim of improving the understanding of this growing family of viral proteins.

Therapeutic potential of MCC950, a specific inhibitor of NLRP3 inflammasome

NOD-like receptor protein 3 (NLRP3), an important intracellular pattern recognition receptor, is a component of the NLRP3 inflammasome along with apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC) and pro-caspase-1. Previous studies have shown that dysregulation of NLRP3 inflammasome may be associated with several human diseases, and therefore blocking NLRP3 inflammasome activation may represent a therapeutic strategy for various diseases. MCC950 is a specific small-molecule inhibitor that selectively blocks activation of the NLRP3 inflammasome. In recent years, research on MCC950 has expanded; its targets are gradually being elucidated, and its metabolism and toxicity have been a focus of study. Preclinical research of MCC950 has yielded promising findings, and MCC950 has shown good efficacy in the treatment of autoimmune diseases, cardiovascular diseases, metabolic diseases and other diseases. Furthermore, clinical trials of MCC950 and other inhibitors of NLRP3 inflammasome have also been conducted. In this review, we discuss the drug targets, metabolism, toxicity and preclinical and clinical research advances of MCC950. We further discuss the clinical therapeutic potential of MCC950 to provide insights for the further study and application of MCC950.

Cell pyroptosis in picornavirus and its potential for treating viral infection

Cell pyroptosis has received increased attention due to the associations between innate immunity and disease, and it has become a major focal point recently due to in-depth studies of cancer. With increased research on pyroptosis, scientists have discovered that it has an essential role in viral infections, especially in the occurrence and development of some picornavirus infections. Many picornaviruses, including Coxsackievirus, a71 enterovirus, human rhinovirus, encephalomyocarditis virus, and foot-and-mouth disease virus induce pyroptosis to varying degrees. This review summarized the mechanisms by which these viruses induce cell pyroptosis, which can be an effective defense against pathogen infection. However, excessive inflammasome activation or pyroptosis also can damage the host's health or aggravate disease progression. Careful approaches that acknowledge this dual effect will aid in the exploration of picornavirus infections and the mechanisms that produce the inflammatory response. This information will promote the development of drugs that can inhibit cell pyroptosis and provide new avenues for future clinical treatment. This article is protected by copyright. All rights reserved.

The Critical Role of Potassium Efflux and Nek7 in Pasteurella multocida-Induced NLRP3 Inflammasome Activation

Pasteurella multocida is a zoonotic pathogen causing respiratory infection in different animal species such as cattle, sheep, pigs, chickens and humans. Inflammasome is a complex assembled by multiple proteins in the cytoplasm and plays an important role in the host defense against microbial infection. Bovine Pasteurella multocida type A (PmCQ2) infection induces NLRP3 inflammasome activation and IL-1β secretion, but the mechanism of PmCQ2-induced activation of NLRP3 inflammasome is still unknown. Therefore, the underlying mechanism was investigated in this study. The results showed that potassium efflux mediated PmCQ2-induced IL-1β secretion and blocking potassium efflux attenuated PmCQ2-induced caspase-1 activation and ASC oligomerization. Furthermore, NIMA-related kinase 7 (Nek7) was also involved in PmCQ2-induced caspase-1 activation and IL-1β secretion. In addition, PmCQ2 infection promoted Nek7-NLRP3 interaction, which is dependent on potassium efflux. In conclusion, our results indicate the critical role of potassium efflux and Nek7 in Pasteurella multocida-induced NLRP3 inflammasome activation, which provides useful information about Pasteurella multocida-induced host immune response.

Component Identification and Analysis of Vesicular Fluid From Swine Infected by Foot-and-Mouth Disease Virus

Foot-and-mouth disease (FMD) is induced by FMD virus (FMDV) and characterized by fever and vesicular (blister-like) lesions. However, the exact composition of the vesicular fluid in pigs infected with FMDV remains unclear. To identify and analyze the components of the vesicular fluid in FMDV-infected domestic pigs, the fluid was collected and subjected to mass spectrometry. Further analyses were conducted using Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genome (KEGG), and protein–protein interaction (PPI). Quantitative ELISA kit for TNF-α, and IFN-α, IFN-β, IL-6, IL-10, IL-1β, and IFN-γ were used to verify the mass spectrometry results. Results showed that 937 proteins were identified in the vesicular fluid from swine after FMDV infection, and bioinformatics analysis indicated that these proteins are related to the innate immune and inflammation pathways. The levels of cytokines involved in the disease-related pathways, tumor necrosis factors, and IL-6 in the fluid samples were significantly increased. This study identified and analyzed the composition of vesicular fluid in pigs after FMD infection for the first time and provided interesting information that help understand the infection and pathogenesis mechanism of FMD. These information will eventually contribute to the prevention and control of FMD.

Senecavirus a 3D Interacts with NLRP3 to Induce IL-1β Production by Activating NF-κB and Ion Channel Signals

Senecavirus A (SVA) infection induces inflammation in animals, such as fever, diarrhea, vesicles and erosions, and even death. The inflammatory cytokine interleukin-1β (IL-1β) plays a pivotal role in inflammatory responses to combat microbes. Although SVA infection can produce inflammatory clinical symptoms, the modulation of IL-1β production by SVA infection remains unknown at present. Here, both in vitro and in vivo, SVA robustly induced IL-1β production in macrophages and pigs. Infection performed in NOD-, LRR-, and pyrin domain-containing three (NLRP3) knockdown cells indicated that NLRP3 is essential for SVA-induced IL-1β secretion. Importantly, we identified that the 1 to 154 amino acid (aa) portion of SVA 3D binds to the NLRP3 NACHT domain to activate NLRP3 inflammasome assembly and IL-1β secretion. In addition, the SVA 3D protein interacts with IKKα and IKKβ to induce NF-κB activation, which facilitates pro-IL-1β transcription. Meanwhile, 3D induces p65 nucleus entry. Moreover, SVA 3D induces calcium influx and potassium efflux, which triggers IL-1β secretion. Ion channels might be related to 3D binding with NLRP3, resulting in NLRP3-ASC complex assembly. We found that 3D protein expression induced tissue hemorrhage and swelling in the mice model. Consistently, expression of 3D in mice caused IL-1β maturation and secretion. In the natural host of pigs, we confirmed that 3D also induced IL-1β production. Our data reveal a novel mechanism underlying the activation of the NLRP3 inflammasome after SVA 3D expression, which provides clues for controlling pig’s inflammation during the SVA infection.

IMPORTANCE Inflammation refers to the response of the immune system to viral, bacterial, and fungal infections or other foreign particles in the body, which can involve the production of a wide array of soluble inflammatory mediators. The NLRP3 inflammasome is one of the best-characterized inflammasome leading to IL-1β production and maturation. Senecavirus A (SVA) is an oncolytic virus that can cause fever, vesicles and erosions, severe fatal diarrhea, and even the sudden death of piglets. In this study, we demonstrated that 1 to 154 aa of SVA polymerase protein 3D interacts with the NACHT domain of NLRP3 to induce IL-1β production via the NF-κB signaling pathway and ion channel signal. Our study unveils the mechanism underlying the regulation of inflammasome assembly and production of IL-1β in response to SVA infection that will help better understand the modulation of host inflammation in pathogens invasion and development of the vaccine.

Activation of the NLRP3 inflammasome and elevation of interleukin-1β secretion in infection by sever fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging phlebovirus that causes a hemorrhagic fever known as the severe fever with thrombocytopenia syndrome (SFTS). Inflammasomes are a molecular platform that are assembled to process pro-caspase 1 and subsequently promote secretion of interleukin (IL)-1β/IL-18 for proinflammatory responses induced upon infection. We hypothesize that inflammasome activation and pyroptosis induced in SFTS results in elevated levels of IL-1β/IL-18 responsible for high fever and hemorrhage in the host, characteristic of SFTS. Here we report that IL-1β secretion was elevated in SFTS patients and infected mice and IL-1β levels appeared to be reversibly associated to disease severity and viral load in patients’ blood. Increased caspase-1 activation, IL-1β/IL-18 secretion, cell death, and processing of gasdermin D were detected, indicating that pyroptosis was induced in SFTSV-infected human peripheral blood monocytes (PBMCs). To characterize the mechanism of pyroptosis induction, we knocked down several NOD-like receptors (NLRs) with respective shRNAs in PBMCs and showed that the NLR family pyrin domain containing 3 (NLRP3) inflammasome was critical for processing pro-caspase-1 and pro-IL-1β. Our data with specific inhibitors for NLRP3 and caspase-1 further showed that activation of the NLRP3 inflammasome was key to caspase-1 activation and IL-1β secretion which may be inhibitory to viral replication in PBMCs infected with SFTSV. The findings in this study suggest that the activation of the NLPR3 inflammasome and pyroptosis, leading to IL-1β/IL-18 secretion during the SFTSV infection, could play important roles in viral pathogenesis and host protection. Pyroptosis as part of innate immunity might be essential in proinflammatory responses and pathogenicty in humans infected with this novel phlebovirus.

FMDV Leader Protein Interacts with the NACHT and LRR Domains of NLRP3 to Promote IL-1β Production

Foot-and-mouth disease virus (FMDV) infection causes inflammatory clinical symptoms, such as high fever and vesicular lesions, even death of animals. Interleukin-1β (IL-1β) is an inflammatory cytokine that plays an essential role in inflammatory responses against viral infection. The viruses have developed multiple strategies to induce the inflammatory responses, including regulation of IL-1β production. However, the molecular mechanism underlying the induction of IL-1β by FMDV remains not fully understood. Here, we found that FMDV robustly induced IL-1β production in macrophages and pigs. Infection of Casp-1 inhibitor-treated cells and NOD-, LRR- and pyrin domain-containing 3 (NLRP3)-knockdown cells indicated that NLRP3 is essential for FMDV-induced IL-1β secretion. More importantly, we found that FMDV Lpro associates with the NACHT and LRR domains of NLRP3 to promote NLRP3 inflammasome assembly and IL-1β secretion. Moreover, FMDV Lpro induces calcium influx and potassium efflux, which trigger NLRP3 activation. Our data revealed the mechanism underlying the activation of the NLRP3 inflammasome after FMDV Lpro expression, thus providing insights for the control of FMDV infection-induced inflammation.

The crosstalk between pattern-recognition receptor signaling and calcium signaling

The innate immune system is the first line of host defense, and it is capable of resisting both exogenous pathogenic challenges and endogenous danger signals via different pattern recognition receptors (PRRs), including Toll-like receptors, retinoic acid-inducible gene-1 (RIG-1)-like receptors, cytosolic DNA sensors, as well as nucleotide-binding oligomerization domain (NOD)-like receptors. After recognizing the pathogen-associated molecular patterns from exogenous microbes or the damage-associated molecular patterns from endogenous immune-stimulatory signals, these PRRs signaling pathways can induce the expression of interferons and inflammatory factors against microbial pathogen invasion and endogenous stresses. Calcium (Ca²⁺) is a second messenger that participates in the modulation of various biological processes, including survival, proliferation, apoptosis, and immune response, and is involved in diverse diseases, such as autoimmune diseases and virus infection. To date, accumulating evidence elucidated that the PRR signaling exhibited a regulatory effect on Ca²⁺ signaling. Meanwhile, Ca²⁺ signaling also played a critical role in controlling biological processes mediated by the PRR adaptors. Since the importance of these two signalings, it would be interesting to clarify the deeper biological implications of their interplays. This review focuses on the crosstalk between Ca²⁺ signaling and PRR signaling to regulate innate immune responses.

The Crucial Role of NLRP3 Inflammasome in Viral Infection-Associated Fibrosing Interstitial Lung Diseases

Idiopathic pulmonary fibrosis (IPF), one of the most common fibrosing interstitial lung diseases (ILD), is a chronic-age-related respiratory disease that rises from repeated micro-injury of the alveolar epithelium. Environmental influences, intrinsic factors, genetic and epigenetic risk factors that lead to chronic inflammation might be implicated in the development of IPF. The exact triggers that initiate the fibrotic response in IPF remain enigmatic, but there is now increasing evidence supporting the role of chronic exposure of viral infection. During viral infection, activation of the NLRP3 inflammasome by integrating multiple cellular and molecular signaling implicates robust inflammation, fibroblast proliferation, activation of myofibroblast, matrix deposition, and aberrant epithelial-mesenchymal function. Overall, the crosstalk of the NLRP3 inflammasome and viruses can activate immune responses and inflammasome-associated molecules in the development, progression, and exacerbation of IPF.

DDX21, a Host Restriction Factor of FMDV IRES-Dependent Translation and Replication

In cells, the contributions of DEAD-box helicases (DDXs), without which cellular life is impossible, are of utmost importance. The extremely diverse roles of the nucleolar helicase DDX21, ranging from fundamental cellular processes such as cell growth, ribosome biogenesis, protein translation, protein–protein interaction, mediating and sensing transcription, and gene regulation to viral manipulation, drew our attention. We designed this project to study virus–host interactions and viral pathogenesis. A pulldown assay was used to investigate the association between foot-and-mouth disease virus (FMDV) and DDX21. Further insight into the DDX21–FMDV interaction was obtained through dual-luciferase, knockdown, overexpression, qPCR, and confocal microscopy assays. Our results highlight the antagonistic feature of DDX21 against FMDV, as it progressively inhibited FMDV internal ribosome entry site (IRES) -dependent translation through association with FMDV IRES domains 2, 3, and 4. To subvert this host helicase antagonism, FMDV degraded DDX21 through its non-structural proteins 2B, 2C, and 3C protease (3C^pro). Our results suggest that DDX21 is degraded during 2B and 2C overexpression and FMDV infection through the caspase pathway; however, DDX21 is degraded through the lysosomal pathway during 3C^pro overexpression. Further investigation showed that DDX21 enhanced interferon-beta and interleukin-8 production to restrict viral replication. Together, our results demonstrate that DDX21 is a novel FMDV IRES trans-acting factor, which negatively regulates FMDV IRES-dependent translation and replication.

The mechanism of antigen-presentation of avian bone marrowed dendritic cells suppressed by infectious bronchitis virus

Dendritic cells are first guard to defend avian infectious bronchitis virus (IBV) infection and invasion. While IBV always suppress dendritic cells and escape the degradation and presentation, which might help viruses to transfer and migrant. Initially, we compared two IBV's function in activating avian bone marrow dendritic cells (BMDCs) and found that both IBV (QX and M41) did not significantly increase surface marker of avian BMDCs. Moreover, a significant decrease of m⁶A modification level in mRNA, but an increased in the ut RNA were observed in avian BMDCs upon the prevalent IBV (QX) infection. Further study found that both non-structural protein 7 (NSP7) and NSP16 inhibited the maturation and cytokines secretion of BMDCs, as well as their antigen-presentation ability. Lastly, we found that gga-miR21, induced by both NSP7 and NSP16, inhibited the antigen presentation of avian BMDCs. Taken together, our results illustrated how IBV inhibited the antigen-presentation of avian DCs.

Activation and Inhibition of the NLRP3 Inflammasome by RNA Viruses

Inflammation refers to the response of the immune system to viral, bacterial, and fungal infections, or other foreign particles in the body, which can involve the production of a wide array of soluble inflammatory mediators. It is important for the development of many RNA virus-infected diseases. The primary factors through which the infection becomes inflammation involve inflammasome. Inflammasomes are proteins complex that the activation is responsive to specific pathogens, host cell damage, and other environmental stimuli. Inflammasomes bring about the maturation of various pro-inflammatory cytokines such as IL-18 and IL-1β in order to mediate the innate immune defense mechanisms. Many RNA viruses and their components, such as encephalomyocarditis virus (EMCV) 2B viroporin, the viral RNA of hepatitis C virus, the influenza virus M2 viroporin, the respiratory syncytial virus (RSV) small hydrophobic (SH) viroporin, and the human rhinovirus (HRV) 2B viroporin can activate the Nod-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome to influence the inflammatory response. On the other hand, several viruses use virus-encoded proteins to suppress inflammation activation, such as the influenza virus NS1 protein and the measles virus (MV) V protein. In this review, we summarize how RNA virus infection leads to the activation or inhibition of the NLRP3 inflammasome.

Role of Mitochondria in Viral Infections

Viral diseases account for an increasing proportion of deaths worldwide. Viruses maneuver host cell machinery in an attempt to subvert the intracellular environment favorable for their replication. The mitochondrial network is highly susceptible to physiological and environmental insults, including viral infections. Viruses affect mitochondrial functions and impact mitochondrial metabolism, and innate immune signaling. Resurgence of host-virus interactions in recent literature emphasizes the key role of mitochondria and host metabolism on viral life processes. Mitochondrial dysfunction leads to damage of mitochondria that generate toxic compounds, importantly mitochondrial DNA, inducing systemic toxicity, leading to damage of multiple organs in the body. Mitochondrial dynamics and mitophagy are essential for the maintenance of mitochondrial quality control and homeostasis. Therefore, metabolic antagonists may be essential to gain a better understanding of viral diseases and develop effective antiviral therapeutics. This review briefly discusses how viruses exploit mitochondrial dynamics for virus proliferation and induce associated diseases.

The DDX23 Negatively Regulates Translation and Replication of Foot-and-Mouth Disease Virus and Is Degraded by 3C Proteinase

DEAD-box helicase 23 (DDX23) is a host nuclear helicase, which is a part of the spliceosomal complex and involved in pre-mRNA splicing. To investigate whether DDX23, an internal ribosomal entry sites transacting factor (ITAF) affects foot-and-mouth disease virus (FMDV) replication and translation through internal ribosome entry site (IRES)-dependent manner. For this, we utilized a pull-down assay, Western blotting, quantitative real-time PCR, confocal microscopy, overexpression and small interfering RNA knockdown, as well as the median tissue culture infective dose. Our findings showed that FMDV infection inhibited DDX23 expression and the overexpression of DDX23 reduced viral replication, however, CRISPR Cas9 knockout/small interfering RNA knockdown increased FMDV replication. FMDV IRES domain III and IV interacted with DDX23, whereas DDX23 interacted with FMDV 3C proteinase and significantly degraded. The enzymatic activity of FMDV 3C proteinase degraded DDX23, whereas FMDV degraded DDX23 via the lysosomal pathway. Additionally, IRES-driven translation was suppressed in DDX23-overexpressing cells, and was enhanced in DDX23 knocked down. Collectively, our results demonstrated that DDX23 negatively affects FMDV IRES-dependent translation, which could be a useful target for the design of antiviral drugs.

The Race between Host Antiviral Innate Immunity and the Immune Evasion Strategies of Herpes Simplex Virus 1

Herpes simplex virus 1 (HSV-1) is very successful in establishing acute and latent infections in humans by counteracting host antiviral innate immune responses. HSV-1 has evolved various strategies to evade host antiviral innate immunity and some cellular survival-associated pathways. Since there is still no vaccine available for HSV-1, a continuous update of information regarding the interaction between HSV-1 infection and the host antiviral innate immunity will provide novel insights to develop new therapeutic strategies for HSV-1 infection and its associated diseases. Here, we update recent studies about how HSV-1 evades the host antiviral innate immunity, specifically how HSV-1 proteins directly or indirectly target the adaptors in the antiviral innate immunity signaling pathways to downregulate the signal transduction. Additionally, some classical intracellular stress responses, which also play important roles in defense of viral invasion, will be discussed here. With a comprehensive review of evasion mechanisms of antiviral innate immunity by HSV-1, we will be able to develop potential new targets for therapies and a possible vaccine against HSV-1 infections.

Advances in Foot-and-Mouth Disease Virus Proteins Regulating Host Innate Immunity

Foot-and-mouth disease (FMD) is a highly contagious disease that affects cloven-hoofed animals such as pigs, cattle, and sheep. The disease is caused by the foot-and-mouth disease virus (FMDV) which has a non-enveloped virion with icosahedral symmetry that encapsulates a positive-sense, single-stranded RNA genome of ∼8.4 kb. FMDV infection causes obvious immunosuppressive effects on the host. In recent years, studies on the immunosuppressive mechanism of FMDV have become a popular topic. In addition, studies have shown that many FMDV proteins are involved in the regulation of host innate immunity and have revealed mechanisms by which FMDV proteins mediate host innate immunity. In this review, advances in studies on the mechanisms of interaction between FMDV proteins and host innate immunity are summarized to provide a comprehensive understanding of FMDV pathogenesis and the theoretical basis for FMD prevention and control.

Viroporins and inflammasomes: A key to understand virus-induced inflammation

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The article provides a summary on cellular receptors involved in virus immunity.

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It summarizes key findings on viroporins, a novel class of viral proteins and their role in the virus life cycle and host cell interactions.

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It presents an overview of the current understanding of inflammasomes complex activation, with special focus on NLRP3.

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It discusses the correlation between viroporins and inflammasomes activation and aggravated inflammatory cytokines production.

Viroporins are virus encoded proteins that alter membrane permeability and can trigger subsequent cellular signals. Oligomerization of viroporin subunits results in formation of a hydrophilic pore which facilitates ion transport across host cell membranes. These viral channel proteins may be involved in different stages of the virus infection cycle. Inflammasomes are large multimolecular complexes best recognized for their ability to control activation of caspase-1, which in turn regulates the maturation of interleukin-1 β (IL-1β) and interleukin 18 (IL-18). IL-1β was originally identified as a pro-inflammatory cytokine able to induce both local and systemic inflammation and a febrile reaction in response to infection or injury. Excessive production of IL-1β is associated with autoimmune and inflammatory diseases. Microbial derivatives, bacterial pore-forming toxins, extracellular ATP and other pathogen-associated molecular patterns trigger activation of NLRP3 inflammasomes. Recent studies have reported that viroporin activity is capable of inducing inflammasome activity and production of IL-1β, where NLRP3 is shown to be regulated by fluxes of K⁺, H⁺ and Ca²⁺ in addition to reactive oxygen species, autophagy and endoplasmic reticulum stress. The aim of this review is to present an overview of the key findings on viroporin activity with special emphasis on their role in virus immunity and as possible activators of inflammasomes.