Induction of the Antiviral Immune Response and Its Circumvention by Coronaviruses

TGEV nonstructural protein ORF3b upregulates the expression of SLA-DR at the transcriptional level in monocyte-derived porcine dendritic cells

Transmissible gastroenteritis virus (TGEV) is a porcine intestinal pathogenic coronavirus that can cause acute intestinal diseases in pigs, especially in suckling piglets under two weeks of age, with a mortality rate of 100 %. Dendritic cells (DCs) are important antigen-presenting cells (APCs) that are essential for the initiation and modulation of immune responses in animals. In this study, we used monocyte-derived porcine DCs as an in vitro model of APCs to further study the pathogenic mechanism of TGEV. Our results demonstrated that TGEV successfully replicates in monocyte-derived porcine DCs, whereas UV-inactivated TGEV failed to infect these cells. Importantly, TGEV infection of DCs led to significant upregulation of swine leukocyte antigen II DR (SLA-DR), a key molecule in the major histocompatibility complex class II (MHC-II) family. We further demonstrated that the ORF3b nonstructural protein of TGEV significantly enhances SLA-DR expression at the transcriptional level in porcine DCs. This study provides new insights into the pathogenic mechanisms of TGEV.

Variation in innate immune responses to porcine epidemic diarrhea virus infection in piglets at different ages

Porcine epidemic diarrhea virus (PEDV) poses a significant threat to pigs, with piglets under seven days old facing a mortality rate of up to 100 %. This study aimed to explore the maturation of the immune system in piglets across different age groups and their corresponding immune responses to PEDV infection. Real-time quantitative PCR was employed to assess the relative mRNA expression of inflammation-related factors in infected pigs compared to non-infected counterparts at varying ages. Additionally, flow cytometry was utilized to analyze the relative counts of CD4+ and CD8+ T cells, as well as CD21+ B cells, in peripheral blood, spleen, mesenteric lymph nodes, and Peyer's patches of piglets at different developmental stages. Our findings revealed a notable increase in IFN-α and IFN-γ, a decrease in TNF-α, and elevated expression of IL-1β, IL-6, IL-10, and IL-17 following PEDV infection. Furthermore, the numbers of CD4+ and CD8+ T cells, along with CD21+ B cells, exhibited a gradual rise with the advancement of piglets' age. Overall, our study underscores the progressive enhancement of piglets' resistance to PEDV infection as their immune system matures over time.

Previous infection with seasonal coronaviruses does not protect male Syrian hamsters from challenge with SARS-CoV-2

SARS-CoV-2 variants and seasonal coronaviruses continue to cause disease and coronaviruses in the animal reservoir pose a constant spillover threat. Importantly, understanding of how previous infection may influence future exposures, especially in the context of seasonal coronaviruses and SARS-CoV-2 variants, is still limited. Here we adopted a step-wise experimental approach to examine the primary immune response and subsequent immune recall toward antigenically distinct coronaviruses using male Syrian hamsters. Hamsters were initially inoculated with seasonal coronaviruses (HCoV-NL63, HCoV-229E, or HCoV-OC43), or SARS-CoV-2 pango B lineage virus, then challenged with SARS-CoV-2 pango B lineage virus, or SARS-CoV-2 variants Beta or Omicron. Although infection with seasonal coronaviruses offered little protection against SARS-CoV-2 challenge, HCoV-NL63-infected animals had an increase of the previously elicited HCoV-NL63-specific neutralizing antibodies during challenge with SARS-CoV-2. On the other hand, primary infection with HCoV-OC43 induced distinct T cell gene signatures. Gene expression profiling indicated interferon responses and germinal center reactions to be induced during more similar primary infection-challenge combinations while signatures of increased inflammation as well as suppression of the antiviral response were observed following antigenically distant viral challenges. This work characterizes and analyzes seasonal coronaviruses effect on SARS-CoV-2 secondary infection and the findings are important for pan-coronavirus vaccine design.

A Detailed Overview of Immune Escape, Antibody Escape, Partial Vaccine Escape of SARS-CoV-2 and Their Emerging Variants With Escape Mutations

The infective SARS-CoV-2 is more prone to immune escape. Presently, the significant variants of SARS-CoV-2 are emerging in due course of time with substantial mutations, having the immune escape property. Simultaneously, the vaccination drive against this virus is in progress worldwide. However, vaccine evasion has been noted by some of the newly emerging variants. Our review provides an overview of the emerging variants' immune escape and vaccine escape ability. We have illustrated a broad view related to viral evolution, variants, and immune escape ability. Subsequently, different immune escape approaches of SARS-CoV-2 have been discussed. Different innate immune escape strategies adopted by the SARS-CoV-2 has been discussed like, IFN-I production dysregulation, cytokines related immune escape, immune escape associated with dendritic cell function and macrophages, natural killer cells and neutrophils related immune escape, PRRs associated immune evasion, and NLRP3 inflammasome associated immune evasion. Simultaneously we have discussed the significant mutations related to emerging variants and immune escape, such as mutations in the RBD region (N439K, L452R, E484K, N501Y, K444R) and other parts (D614G, P681R) of the S-glycoprotein. Mutations in other locations such as NSP1, NSP3, NSP6, ORF3, and ORF8 have also been discussed. Finally, we have illustrated the emerging variants' partial vaccine (BioNTech/Pfizer mRNA/Oxford-AstraZeneca/BBIBP-CorV/ZF2001/Moderna mRNA/Johnson & Johnson vaccine) escape ability. This review will help gain in-depth knowledge related to immune escape, antibody escape, and partial vaccine escape ability of the virus and assist in controlling the current pandemic and prepare for the next.

A decoy strategy to activate the immune system

An approach comprising a novel fusion protein and inactivated virus, as a more efficacious vaccine against invading viruses is presented, using SARS-CoV-2 as a most prominent example. The fusion protein consists of the Hepatitis B surface antigen (HBsAg) conjugated to the N-terminal helix (NTH) of Angiotensin-Converting Enzyme 2 (ACE2), which is the receptor for SARS-CoV-2. For vaccination, this fusion protein is to be administered together with the whole killed virus. The NTH would bind to the Receptor Binding Domain (RBD) of the Spike protein of the killed virus. Due to HBsAg acting as a decoy, immune responses would be mounted. Neutralizing antibodies (NAbs) pre-existing in people already vaccinated with the recombinant Hepatitis B vaccine, fresh production of NAbs, and NAbs produced by memory B cells would bind to the HBsAg. This would lead to "presentation" of the killed virus to elements of the immune system at close range. Also, there would be enhanced opsonization and effective antigen presentation. This two-component vaccine could be a platform strategy, wherein HBsAg could be linked to the part of the cellular receptor that any new intractable virus binds to, and is administered together with whole inactivated virus. Now, the same fusion protein, administered by itself to persons with infection, would have therapeutic action, yet by harnessing elements of the immune system. NAbs would bind to the fusion protein as above, the NTH of which would bind to the RBDs of the infecting virus, which, in effect would be neutralized.

Acute Infection of Viral Pathogens and Their Innate Immune Escape

Viral infections can cause rampant disease in human beings, ranging from mild to acute, that can often be fatal unless resolved. An acute viral infection is characterized by sudden or rapid onset of disease, which can be resolved quickly by robust innate immune responses exerted by the host or, instead, may kill the host. Immediately after viral infection, elements of innate immunity, such as physical barriers, various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, provide the first line of defense for viral clearance. Innate immunity not only plays a critical role in rapid viral clearance but can also lead to disease progression through immune-mediated host tissue injury. Although elements of antiviral innate immunity are armed to counter the viral invasion, viruses have evolved various strategies to escape host immune surveillance to establish successful infections. Understanding complex mechanisms underlying the interaction between viruses and host’s innate immune system would help develop rational treatment strategies for acute viral infectious diseases. In this review, we discuss the pathogenesis of acute infections caused by viral pathogens and highlight broad immune escape strategies exhibited by viruses.

Immune Responses in Patients with COVID-19: An Overview

Since late 2019, the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has resulted in more than 143 million confirmed infections and more than 3 million deaths worldwide (as of publication time). In this article, we discuss current knowledge of immune responses that confer protection to more than 80% of the people who have been infected and possible mechanisms by which the virus escapes immune surveillance in people who develop severe disease and those who die from the disease. We also discuss the differences in the immune responses by which, in most children, the infection results in only mild disease, although causing severe disease in some adults. Understanding these differences in both the innate and adaptive immune responses among these people can lead to the development of biotherapeutic treatment modalities that could modulate immune responses to offer protection against SARS-CoV-2 and block the ability of the virus to cause severe disease or death in humans. [Pediatr Ann. 2021;50(5):e222-e226.].

RNA Epigenetics: Fine-Tuning Chromatin Plasticity and Transcriptional Regulation, and the Implications in Human Diseases

Chromatin structure plays an essential role in eukaryotic gene expression and cell identity. Traditionally, DNA and histone modifications have been the focus of chromatin regulation; however, recent molecular and imaging studies have revealed an intimate connection between RNA epigenetics and chromatin structure. Accumulating evidence suggests that RNA serves as the interplay between chromatin and the transcription and splicing machineries within the cell. Additionally, epigenetic modifications of nascent RNAs fine-tune these interactions to regulate gene expression at the co- and post-transcriptional levels in normal cell development and human diseases. This review will provide an overview of recent advances in the emerging field of RNA epigenetics, specifically the role of RNA modifications and RNA modifying proteins in chromatin remodeling, transcription activation and RNA processing, as well as translational implications in human diseases.