Interference of the Zika Virus E-Protein With the Membrane Attack Complex of the Complement System

Lnc-DARVR/miR-365-1-5p/LAMB1 axis regulates rotavirus replication via the complement C3 pathway

Antiviral effectors and cytokines are critical components of host innate immunity. However, the regulatory mechanisms governing the roles of these molecules in host-virus interactions are still unclear. Although long non-coding RNAs (lncRNAs) have been recognized as key players in various biological processes, their involvement in the complement system of host antiviral defenses remains to be explored. In this study, we discovered a novel, unannotated lncRNA, called DARVR. DARVR was found to be an intergenic lncRNA and inhibited rotavirus (RV) replication in MA104 cells. Mechanistically, we found that complement 3 (C3) was upregulated following RV infection in a LAMB1-dependent manner. However, LAMB1 expression was downregulated by miR-365-1-5p, resulting in the inhibition of the C3-mediated antiviral reaction. However, DARVR functioned as a competing endogenous RNA against miR-365-1-5p, promoting the expression of LAMB1 and thereby enhancing C3 activity and inhibiting RV replication. These results not only provide evidence demonstrating the involvement of lncRNAs in the regulation of RV infection but also highlight the role of complement factors in host innate immunity.

IMPORTANCE

Long non-coding RNAs (lncRNAs) play versatile and critical roles in host-virus interactions, offering significant potential for developing targeted therapies to prevent or treat viral infections. Despite their importance, the involvement of lncRNAs in rotavirus infection remains underexplored. This study identifies a novel lncRNA that enhances complement factor C3 activity through the competing endogenous RNA (ceRNA) mechanism, effectively inhibiting rotavirus replication across different subtypes. These findings underscore the complex molecular interplay regulating complement factor activity during rotavirus infection and provide valuable insights into the host's antiviral mechanisms. This research paves the way for innovative therapeutic strategies targeting lncRNAs and complement factors to combat viral infections more effectively.

Generating prophylactic immunity against arboviruses in vertebrates and invertebrates

The World Health Organization recently declared a global initiative to control arboviral diseases. These are mainly caused by pathogenic flaviviruses (such as dengue, yellow fever and Zika viruses) and alphaviruses (such as chikungunya and Venezuelan equine encephalitis viruses). Vaccines represent key interventions for these viruses, with licensed human and/or veterinary vaccines being available for several members of both genera. However, a hurdle for the licensing of new vaccines is the epidemic nature of many arboviruses, which presents logistical challenges for phase III efficacy trials. Furthermore, our ability to predict or measure the post-vaccination immune responses that are sufficient for subclinical outcomes post-infection is limited. Given that arboviruses are also subject to control by the immune system of their insect vectors, several approaches are now emerging that aim to augment antiviral immunity in mosquitoes, including Wolbachia infection, transgenic mosquitoes, insect-specific viruses and paratransgenesis. In this Review, we discuss recent advances, current challenges and future prospects in exploiting both vertebrate and invertebrate immune systems for the control of flaviviral and alphaviral diseases.

Microbial evasion of the complement system: a continuous and evolving story

The complement system is a fundamental part of the innate immune system that plays a key role in the battle of the human body against invading pathogens. Through its three pathways, represented by the classical, alternative, and lectin pathways, the complement system forms a tightly regulated network of soluble proteins, membrane-expressed receptors, and regulators with versatile protective and killing mechanisms. However, ingenious pathogens have developed strategies over the years to protect themselves from this complex part of the immune system. This review briefly discusses the sequence of the complement activation pathways. Then, we present a comprehensive updated overview of how the major four pathogenic groups, namely, bacteria, viruses, fungi, and parasites, control, modulate, and block the complement attacks at different steps of the complement cascade. We shed more light on the ability of those pathogens to deploy more than one mechanism to tackle the complement system in their path to establish infection within the human host.

Pathogenesis and Manifestations of Zika Virus-Associated Ocular Diseases

Zika virus (ZIKV) is mosquito-borne flavivirus that caused a significant public health concern in French Polynesia and South America. The two major complications that gained the most media attention during the ZIKV outbreak were Guillain-Barré syndrome (GBS) and microcephaly in newborn infants. The two modes of ZIKV transmission are the vector-borne and non-vector borne modes of transmission. Aedes aegypti and Aedes albopictus are the most important vectors of ZIKV. ZIKV binds to surface receptors on permissive cells that support infection and replication, such as neural progenitor cells, dendritic cells, dermal fibroblasts, retinal pigment epithelial cells, endothelial cells, macrophages, epidermal keratinocytes, and trophoblasts to cause infection. The innate immune response to ZIKV infection is mediated by interferons and natural killer cells, whereas the adaptive immune response is mediated by CD8⁺T cells, Th1 cells, and neutralizing antibodies. The non-structural proteins of ZIKV, such as non-structural protein 5, are involved in the evasion of the host's immune defense mechanisms. Ocular manifestations of ZIKV arise from the virus' ability to cross both the blood-brain barrier and blood-retinal barrier, as well as the blood-aqueous barrier. Most notably, this results in the development of GBS, a rare neurological complication in acute ZIKV infection. This can yield ocular symptoms and signs. Additionally, infants to whom ZIKV is transmitted congenitally develop congenital Zika syndrome (CZS). The ocular manifestations are widely variable, and include nonpurulent conjunctivitis, anterior uveitis, keratitis, trabeculitis, congenital glaucoma, microphthalmia, hypoplastic optic disc, and optic nerve pallor. There are currently no FDA approved therapeutic agents for treating ZIKV infections and, as such, a meticulous ocular examination is an important aspect of the diagnosis. This review utilized several published articles regarding the ocular findings of ZIKV, antiviral immune responses to ZIKV infection, and the pathogenesis of ocular manifestations in individuals with ZIKV infection. This review summarizes the current knowledge on the viral immunology of ZIKV, interactions between ZIKV and the host's immune defense mechanism, pathological mechanisms, as well as anterior and posterior segment findings associated with ZIKV infection.

New Insights into the Role of the Complement System in Human Viral Diseases

The complement system (CS) is part of the human immune system, consisting of more than 30 proteins that play a vital role in the protection against various pathogens and diseases, including viral diseases. Activated via three pathways, the classical pathway (CP), the lectin pathway (LP), and the alternative pathway (AP), the complement system leads to the formation of a membrane attack complex (MAC) that disrupts the membrane of target cells, leading to cell lysis and death. Due to the increasing number of reports on its role in viral diseases, which may have implications for research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), this review aims to highlight significant progress in understanding and defining the role of the complement system in four groups of diseases of viral etiology: (1) respiratory diseases; (2) acute liver failure (ALF); (3) disseminated intravascular coagulation (DIC); and (4) vector-borne diseases (VBDs). Some of these diseases already present a serious global health problem, while others are a matter of concern and require the collaboration of relevant national services and scientists with the World Health Organization (WHO) to avoid their spread.

Functional Identification of Complement Factor D and Analysis of Its Expression during GCRV Infection in Grass Carp (Ctenopharyngodon idella)

Complement factor D (Df) is a serine protease well known for activating the alternative pathway (AP) in mammals by promoting the cleavage of complement component 3 (C3), thus becoming involved in innate defense. In teleost fish, however, the functional mechanisms of Df in the AP and against pathogen infection are far from clear. In the present study, we cloned and characterized the Df gene, CiDf, from grass carp (Ctenopharyngodon idella) and analyzed its function in promoting C3 cleavage and expression changes after grass carp reovirus (GCRV) infection. The open reading frame of CiDf was found to be 753 bp, encoding 250 amino acids with a molecular mass of 27.06 kDa. CiDf harbors a conserved Tryp_SPc domain, with three conserved residues representing the catalytic triad and three conserved binding sites in the substrate specificity pocket. Pairwise alignment showed that CiDf shares the highest identity (96%) and similarity (98%) with Df from Anabarilius grahami. Phylogenetic analysis indicated that CiDf and other fish Dfs formed a distinct evolutionary branch. Similar to most Dfs from other vertebrates, the CiDf gene structure is characterized by four introns and five exons. The incubation of recombinant CiDf protein with grass carp serum significantly increased the C3b content, demonstrating the conserved function of CiDf in the AP in promoting C3 cleavage, similar to Dfs in mammals. CiDf mRNA expression was widely detected in various tissues and levels were relatively higher in the liver, spleen, and intestine of grass carp. During GCRV infection over a 168-hour period, a high level of CiDf mRNA expression in the liver, spleen, and intestine was maintained at 144 and 168 h, suggesting AP activity at the late stage of GCRV infection. Collectively, the above results reveal the conserved structure and function of CiDf and its distinct expression patterns after GCRV infection, which provide a key basis for studying the roles of Df and AP during GCRV infection in the grass carp C. idella.

Incorporation of CD55 into the Zika Viral Envelope Contributes to Its Stability against Human Complement

The rapid spread of the virus in Latin America and the association of the infection with microcephaly in newborns or Guillain–Barré Syndrome in adults prompted the WHO to declare the Zika virus (ZIKV) epidemic to be an international public health emergency in 2016. As the virus was first discovered in monkeys and is spread not only by mosquitos but also from human to human, we investigated the stability to the human complement of ZIKV derived from mosquito (ZIKVInsect), monkey (ZIKVVero), or human cells (ZIKVA549 and ZIKVFibro), respectively. At a low serum concentration (10%), which refers to complement concentrations found on mucosal surfaces, the virus was relatively stable at 37 °C. At higher complement levels (up to 50% serum concentration), ZIKV titers differed significantly depending on the cell line used for the propagation of the virus. While the viral titer of ZIKVInsect decreased about two orders in magnitude, when incubated with human serum, the virus derived from human cells was more resistant to complement-mediated lysis (CML). By virus-capture assay and Western blots, the complement regulator protein CD55 was identified to be incorporated into the viral envelope. Blocking of CD55 by neutralizing Abs significantly increased the sensitivity to human complement. Taken together, these data indicate that the incorporation of CD55 from human cells contributes to the stability of ZIKV against complement-mediated virolysis.

Virus-Encoded Complement Regulators: Current Status

Viruses require a host for replication and survival and hence are subjected to host immunological pressures. The complement system, a crucial first response of the host immune system, is effective in targeting viruses and virus-infected cells, and boosting the antiviral innate and acquired immune responses. Thus, the system imposes a strong selection pressure on viruses. Consequently, viruses have evolved multiple countermeasures against host complement. A major mechanism employed by viruses to subvert the complement system is encoding proteins that target complement. Since viruses have limited genome size, most of these proteins are multifunctional in nature. In this review, we provide up to date information on the structure and complement regulatory functions of various viral proteins.