Inhibitory Effect of IL-1β on HBV and HDV Replication and HB Antigen-Dependent Modulation of Its Secretion by Macrophages

Co-infection with the hepatitis B virus and hepatitis delta virus (HDV) leads to the most aggressive form of viral hepatitis. Using in vitro infection models, we confirmed that IL-1β, a crucial innate immune molecule for pathogen control, was very potent against HBV from different genotypes. Additionally, we demonstrated for the first time a strong and rapid antiviral effect induced by very low doses of IL-1β against HDV. In parallel, using co-culture assays, we demonstrated that monocytes exposed to HBV, and in particular to HBsAg, during differentiation into pro-inflammatory macrophages secreted less IL-1β. Altogether, our data emphasize the importance of developing combined antiviral strategies that would, for instance, reduce the secretion of HBsAg and stimulate the immune system to produce endogenous IL-1β efficient against both HBV and HDV.

Omicron infection enhances neutralizing immunity against the Delta variant

Omicron has been shown to be highly transmissible and have extensive evasion of neutralizing antibody immunity elicited by vaccination and previous SARS-CoV-2 infection. Omicron infections are rapidly expanding worldwide often in the face of high levels of Delta infections. Here we characterized developing immunity to Omicron and investigated whether neutralizing immunity elicited by Omicron also enhances neutralizing immunity of the Delta variant. We enrolled both previously vaccinated and unvaccinated individuals who were infected with SARS-CoV-2 in the Omicron infection wave in South Africa soon after symptom onset. We then measured their ability to neutralize both Omicron and Delta virus at enrollment versus a median of 14 days after enrollment. Neutralization of Omicron increased 14-fold over this time, showing a developing antibody response to the variant. Importantly, there was an enhancement of Delta virus neutralization, which increased 4.4-fold. The increase in Delta variant neutralization in individuals infected with Omicron may result in decreased ability of Delta to re-infect those individuals. Along with emerging data indicating that Omicron, at this time in the pandemic, is less pathogenic than Delta, such an outcome may have positive implications in terms of decreasing the Covid-19 burden of severe disease.

A Mathematical Model for Early HBV and -HDV Kinetics during Anti-HDV Treatment

Hepatitis delta virus (HDV) is an infectious subviral agent that can only propagate in people infected with hepatitis B virus (HBV). HDV/HBV infection is considered to be the most severe form of chronic viral hepatitis. In this contribution, a mathematical model for the interplay between HDV and HBV under anti-HDV treatment is presented. Previous models were not designed to account for the observation that HBV rises when HDV declines with HDV-specific therapy. In the simple model presented here, HDV and HBV kinetics are coupled, giving rise to an improved viral kinetic model that simulates the early interplay of HDV and HBV during anti-HDV therapy.

Hepatitis delta virus genome RNA synthesis initiates at position 1646 with a non-templated guanosine

Hepatitis delta virus (HDV) is a significant human pathogen that causes acute and chronic liver disease; there is no licensed therapy. HDV is a circular negative-sense ssRNA virus that produces three RNAs in infected cells: genome, antigenome and mRNA; the latter encodes hepatitis delta antigen, the viral protein. These RNAs are synthesized by host DNA-dependent RNA polymerase acting as an RNA-dependent RNA polymerase. Although HDV genome RNA accumulates to high levels in infected cells, the mechanism by which this process occurs remains poorly understood. For example, the nature of the 5’ end of the genome, including the synthesis start site and its chemical composition, are not known. Analysis of this process has been challenging because the initiation site is part of an unstable precursor in the rolling circle mechanism by which HDV genome RNA is synthesized. In this study, circular HDV antigenome RNAs synthesized in vitro were used to directly initiate HDV genome RNA synthesis in transfected cells, thus enabling detection of the 5’ end of the genome RNA. The 5’ end of this RNA is capped, as expected for a Pol II product. Initiation begins at position 1646 on the genome, which is located near the loop end proximal to the start site for HDAg mRNA synthesis. Unexpectedly, synthesis begins with a guanosine that is not conventionally templated by the HDV RNA. IMPORTANCE Hepatitis delta virus (HDV) is a unique virus that causes severe liver disease. It uses host RNA Polymerase II to copy its circular RNA genome in a unique and poorly understood process. Although the virus RNA accumulates to high levels within infected cells, it is not known how synthesis of the viral RNA begins, nor even where on the genome synthesis starts. Here, we identify the start site for the initiation of HDV genome RNA synthesis as position 1646, which is at one end of the closed hairpin-like structure of the viral RNA. The 5’ end of the RNA is capped, as expected for Pol II products. However, RNA synthesis begins with a guanosine that is not present in the genome. Thus, although HDV uses Pol II to synthesize the viral genome, some details of the initiation process are different. These differences could be important for successfully targeting virus replication.

A Rapid Point-of-Care Test for the Serodiagnosis of Hepatitis Delta Virus Infection

Hepatitis Delta virus (HDV) is a satellite of the Hepatitis B virus (HBV) and causes severe liver disease. The estimated prevalence of 15–20 million infected people worldwide may be underestimated as international diagnostic guidelines are not routinely followed. Possible reasons for this include the limited awareness among healthcare providers, the requirement for costly equipment and specialized training, and a lack of access to reliable tests in regions with poor medical infrastructure. In this study, we developed an HDV rapid test for the detection of antibodies against the hepatitis delta antigen (anti-HDV) in serum and plasma. The test is based on a novel recombinant large hepatitis delta antigen that can detect anti-HDV in a concentration-dependent manner with pan-genotypic activity across all known HDV genotypes. We evaluated the performance of this test on a cohort of 474 patient samples and found that it has a sensitivity of 94.6% (314/332) and a specificity of 100% (142/142) when compared to a diagnostic gold-standard ELISA. It also works robustly for a broad range of anti-HDV titers. We anticipate this novel HDV rapid test to be an important tool for epidemiological studies and clinical diagnostics, especially in regions that currently lack access to reliable HDV testing.

Constraint of Base Pairing on HDV Genome Evolution

The hepatitis delta virus is a single-stranded circular RNA virus, which is characterized by high self-complementarity. About 70% of the genome sequences can form base-pairs with internal nucleotides. There are many studies on the evolution of the hepatitis delta virus. However, the secondary structure has not been taken into account in these studies. In this study, we developed a method to examine the effect of base pairing as a constraint on the nucleotide substitutions during the evolution of the hepatitis delta virus. The method revealed that the base pairing can reduce the evolutionary rate in the non-coding region of the virus. In addition, it is suggested that the non-coding nucleotides without base pairing may be under some constraint, and that the intensity of the constraint is weaker than that by the base pairing but stronger than that on the synonymous site.

Comprehensive Analysis of Hepatitis Delta Virus Assembly Determinants According to Genotypes: Lessons From a Study of 526 Hepatitis Delta Virus Clinical Strains

Human hepatitis Delta virus (HDV) infection is associated to the most severe viral hepatic disease, including severe acute liver decompensation and progression to cirrhosis, and hepatocellular carcinoma. HDV is a satellite of hepatitis B virus (HBV) that requires the HBV envelope proteins for assembly of HDV virions. HDV and HBV exhibit a large genetic diversity that extends, respectively to eight (HDV-1 to -8) and to ten (HBV/A to/J) genotypes. Molecular determinants of HDV virion assembly consist of a C-terminal Proline-rich domain in the large Hepatitis Delta Antigen (HDAg) protein, also known as the Delta packaging domain (DPD) and of a Tryptophan-rich domain, the HDV matrix domain (HMD) in the C-terminal region of the HBV envelope proteins. In this study, we performed a systematic genotyping of HBV and HDV in a cohort 1,590 HDV-RNA-positive serum samples collected between 2001 to 2014, from patients originated from diverse parts of the world, thus reflecting a large genetic diversity. Among these samples, 526 HBV (HBV/A, B, C, D, E, and G) and HDV (HDV-1, 2, 3, and 5 to -8) genotype couples could be obtained. We provide results of a comprehensive analysis of the amino-acid sequence conservation within the HMD and structural and functional features of the DPD that may account for the yet optimal interactions between HDV and its helper HBV.