Thermal Inactivation of Hepatitis E Virus in Pork Products Estimated with a Semiquantitative Infectivity Assay

Hepatitis E virus genotype 3 (HEV-3) is a food-borne pathogen causative of hepatitis E infections in humans. In Europe, HEV-3 is mainly transmitted through the consumption of raw or undercooked pork. In order to determine the effectiveness of control measures that can be taken in the industry or by the consumer, it is pivotal to determine the infectivity of HEV present in pork products after thermal food-processing steps. First, we implemented a method for the detection of infectious HEV-3c and HEV-3e in a cell culture medium and in extracts from inoculated pork products. Next, we investigated the effect of the thermal inactivation of HEV by mimicking food-processing steps specific for dried sausage and liver homogenate matrices. After four weeks, HEV-inoculated dried sausage subjected to 21 °C or lower temperatures was still infectious. For the liver homogenate, the highest HEV-3c/e inactivation of the conditions tested was observed at 71 °C for five min or longer. Finally, our method was able to successfully detect and estimate viral loads of infectious HEV in naturally infected pig livers. Our data provide a basis for the future use of the quantitative microbial risk assessment of infectious HEV in pork products that are subjected to thermal food processing steps.

The Long Non-Coding Antisense RNA JHDM1D-AS1 Regulates Inflammatory Responses in Human Monocytes

Monocytes are key players in innate immunity, with their ability to regulate inflammatory responses and combat invading pathogens. There is a growing body of evidence indicating that long non-coding RNA (lncRNA) participate in various cellular biological processes, including the innate immune response. The immunoregulatory properties of numerous lncRNAs discovered in monocytes remain largely unexplored. Here, by RNA sequencing, we identified a lncRNA JHDM1D-AS1, which was upregulated in blood monocytes obtained from patients with sepsis relative to healthy controls. JHDM1D-AS1 expression was induced in primary human monocytes exposed to Toll-like receptor ligands, such as lipopolysaccharide (LPS), or bacteria. The inducibility of JHDM1D-AS1 expression in monocytes depended, at least in part, on nuclear factor-κB activation. JHDM1D-AS1 knockdown experiments in human monocyte-derived macrophages revealed significantly enhanced expression of inflammatory mediators, before and after exposure to LPS, relative to control cells. Specifically, genes involved in inflammatory responses were upregulated (e.g., CXCL2, CXCL8, IL1RN, TREM1, TNF, and IL6), whereas genes involved in anti-inflammatory pathways were downregulated (e.g., SOCS1 and IL10RA). JHDM1D-AS1 overexpression in a pro-monocytic cell line revealed diminished pro-inflammatory responses subsequent to LPS challenge. Collectively, these findings identify JHDM1D-AS1 as a potential anti-inflammatory mediator induced in response to inflammatory stimuli.

Crosstalk between R848 and abortive HIV-1 RNA-induced signaling enhances antiviral immunity

Pathogens trigger multiple pattern recognition receptors (PRRs) that together dictate innate and adaptive immune responses. Understanding the crosstalk between PRRs is important to enhance vaccine efficacy. Abortive HIV-1 RNA transcripts are produced during acute and chronic HIV-1 infection and are known ligands for different PRRs, leading to antiviral and proinflammatory responses. Here, we have investigated the crosstalk between responses induced by these 58 nucleotide-long HIV-1 RNA transcripts and different TLR ligands. Costimulation of dendritic cells (DCs) with abortive HIV-1 RNA and TLR7/8 agonist R848, but not other TLR agonists, resulted in enhanced antiviral type I IFN responses as well as adaptive immune responses via the induction of DC-mediated T helper 1 (T_H 1) responses and IFNγ⁺ CD8⁺ T cells. Our data underscore the importance of crosstalk between abortive HIV-1 RNA and R848-induced signaling for the induction of effective antiviral immunity.

DDX3X structural analysis: Implications in the pharmacology and innate immunity

The human DEAD-Box Helicase 3 X-Linked (DDX3X) is an ATP-dependent RNA helicase involved in virtually every step of RNA metabolism, ranging from transcription regulation in the nucleus to translation initiation and stress granule (SG) formation, and plays crucial roles in innate immunity, as well as tumorigenesis and viral infections.

This review discusses latest advances in DDX3X biology and structure-function relationship, including the implications of the recent DDX3X crystal structure in complex with double stranded RNA for RNA metabolism, DDX3X involvement in the cross-talk between innate immune responses and cell stress adaptation, and the roles of DDX3X in controlling cell fate.

•

The human DDX3X, an ATP-dependent RNA helicase, plays a central role in a variety of cellular processes involving RNA.

•

DDX3X is implicated in antiviral signalling pathways.

•

DDX3X interacts with full-length NLRP3 and its NACHT domain.

•

The recent crystal structure of DDX3X in complex with dsRNA offers a model for understanding its binding to the HIV-1 TAR hairpin sequence.

Abortive HIV-1 RNA induces pro-IL-1β maturation via protein kinase PKR and inflammasome activation in humans

The proinflammatory cytokine IL-1β mediates high levels of immune activation observed during acute and chronic human immunodeficiency virus 1 (HIV-1) infection. Little is known about the mechanisms that drive IL-1β activation during HIV-1 infection. Here, we have identified a crucial role for abortive HIV-1 RNAs in inducing IL-1β in humans. Abortive HIV-1 RNAs were sensed by protein kinase RNA-activated (PKR), which triggered activation of the canonical NLRP3 inflammasome and caspase-1, leading to pro-IL-1β processing and secretion. PKR activated the inflammasome via ROS generation and MAP kinases ERK1/2, JNK, and p38. Inhibition of PKR during HIV-1 infection blocked IL-1β production. As abortive HIV-1 RNAs are produced during productive infection and latency, our data strongly suggest that targeting PKR signaling might attenuate immune activation during acute and chronic HIV-1 infection.

Synthetic Abortive HIV-1 RNAs Induce Potent Antiviral Immunity

Strong innate and adaptive immune responses are paramount in combating viral infections. Dendritic cells (DCs) detect viral infections via cytosolic RIG-I like receptors (RLRs) RIG-I and MDA5 leading to MAVS-induced immunity. The DEAD-box RNA helicase DDX3 senses abortive human immunodeficiency virus 1 (HIV-1) transcripts and induces MAVS-dependent type I interferon (IFN) responses, suggesting that abortive HIV-1 RNA transcripts induce antiviral immunity. Little is known about the induction of antiviral immunity by DDX3-ligand abortive HIV-1 RNA. Here we synthesized a 58 nucleotide-long capped RNA (HIV-1 Cap-RNA₅₈) that mimics abortive HIV-1 RNA transcripts. HIV-1 Cap-RNA₅₈ induced potent type I IFN responses in monocyte-derived DCs, monocytes, macrophages and primary CD1c⁺ DCs. Compared with RLR agonist poly-I:C, HIV-1 Cap-RNA₅₈ induced comparable levels of type I IFN responses, identifying HIV-1 Cap-RNA₅₈ as a potent trigger of antiviral immunity. In monocyte-derived DCs, HIV-1 Cap-RNA₅₈ activated the transcription factors IRF3 and NF-κB. Moreover, HIV-1 Cap-RNA₅₈ induced DC maturation and the expression of pro-inflammatory cytokines. HIV-1 Cap-RNA₅₈-stimulated DCs induced proliferation of CD4⁺ and CD8⁺ T cells and differentiated naïve T helper (T_H) cells toward a T_H2 phenotype. Importantly, treatment of DCs with HIV-1 Cap-RNA₅₈ resulted in an efficient antiviral innate immune response that reduced ongoing HIV-1 replication in DCs. Our data strongly suggest that HIV-1 Cap-RNA₅₈ induces potent innate and adaptive immune responses, making it an interesting addition in vaccine design strategies.

DDX3 in HIV-1 infection and sensing: A paradox

HIV-1 sensors and their signaling features have been an ongoing topic of intense research over the last decade, as these mechanisms fail to establish protective immunity against HIV-1. Here, we discuss how HIV-1 infects dendritic cells (DCs) and which sensors play a role in recognizing viral DNA and RNA in these specialized immune cells. We will elaborate on the RNA helicase DDX3, which is crucial in translation initiation of HIV-1 mRNA, but also fulfills an important role as RNA sensor and inducer of antiviral immunity in DCs. As DDX3 is indispensable for HIV-1 replication, the virus cannot escape sensing by DDX3, which is an important aspect of its function. Last but not least, we will discuss how HIV-1 suppresses DDX3 sensing and how this impacts the viral load in HIV-1-infected individuals.

C-Type Lectin Receptors in Antiviral Immunity and Viral Escape

C-type lectin receptors (CLRs) are important pattern recognition receptors involved in recognition and induction of adaptive immunity to pathogens. Certain CLRs play an important role in viral infections as they efficiently interact with viruses. However, it has become clear that deadly viruses subvert the function of CLRs to escape antiviral immunity and promote infection. In particular, viruses target CLRs to suppress or modulate type I interferons that play a central role in the innate and adaptive defense against viruses. In this review, we discuss the function of CLRs in binding to enveloped viruses like HIV-1 and Dengue virus, and how uptake and signaling cascades have decisive effects on the outcome of infection.

Presenting native-like HIV-1 envelope trimers on ferritin nanoparticles improves their immunogenicity

Background

Presenting vaccine antigens in particulate form can improve their immunogenicity by enhancing B cell activation.

Findings

We describe ferritin-based protein nanoparticles that display multiple copies of native-like HIV-1 envelope glycoprotein trimers (BG505 SOSIP.664). Trimer-bearing nanoparticles were significantly more immunogenic than trimers in both mice and rabbits. Furthermore, rabbits immunized with the trimer-bearing nanoparticles induced significantly higher neutralizing antibody responses against most tier 1A viruses, and higher responses (but not significantly), to several tier 1B viruses and the autologous tier 2 virus than when the same trimers were delivered as soluble proteins.

Conclusions

This or other nanoparticle designs may be practical ways to improve the immunogenicity of envelope glycoprotein trimers.