Enteroviral conjunctivitis and its neurological complications

Structure of Human Enterovirus 70 and Its Inhibition by Capsid-Binding Compounds

Enterovirus 70 (EV70) is a human pathogen belonging to the family Picornaviridae. EV70 is transmitted by eye secretions and causes acute hemorrhagic conjunctivitis, a serious eye disease. Despite the severity of the disease caused by EV70, its structure is unknown. Here, we present the structures of the EV70 virion, altered particle, and empty capsid determined by cryo-electron microscopy. The capsid of EV70 is composed of the subunits VP1, VP2, VP3, and VP4. The partially collapsed hydrophobic pocket located in VP1 of the EV70 virion is not occupied by a pocket factor, which is commonly present in other enteroviruses. Nevertheless, we show that the pocket can be targeted by the antiviral compounds WIN51711 and pleconaril, which block virus infection. The inhibitors prevent genome release by stabilizing EV70 particles. Knowledge of the structures of complexes of EV70 with inhibitors will enable the development of capsid-binding therapeutics against this virus.

IMPORTANCE Globally distributed enterovirus 70 (EV70) causes local outbreaks of acute hemorrhagic conjunctivitis. The discharge from infected eyes enables the high-efficiency transmission of EV70 in overcrowded areas with low hygienic standards. Currently, only symptomatic treatments are available. We determined the structures of EV70 in its native form, the genome release intermediate, and the empty capsid resulting from genome release. Furthermore, we elucidated the structures of EV70 in complex with two inhibitors that block virus infection, and we describe the mechanism of their binding to the virus capsid. These results enable the development of therapeutics against EV70.

Enterovirus D: A Small but Versatile Species

Enteroviruses (EVs) from the D species are the causative agents of a diverse range of infectious diseases in spite of comprising only five known members. This small clade has a diverse host range and tissue tropism. It contains types infecting non-human primates and/or humans, and for the latter, they preferentially infect the eye, respiratory tract, gastrointestinal tract, and nervous system. Although several Enterovirus D members, in particular EV-D68, have been associated with neurological complications, including acute myelitis, there is currently no effective treatment or vaccine against any of them. This review highlights the peculiarities of this viral species, focusing on genome organization, functional elements, receptor usage, and pathogenesis.

Chapter 4 Picornavirus infections

The oldest member of the Picornaviruses group is polio virus, which was recognized early by clinicians because of its characteristic paralytic disease. This chapter examines the polio virus in regard to its virology, disease, and prevention by vaccines and chemoprophylaxis. Polio has been well controlled in most developed countries using live or inactivated vaccines. Research work has intensified using genetic engineering techniques to produce live attenuated viruses with defined and stable mutations so as to prevent reversion to virulence, and also to produce immunogenic oligopeptides or proteins for a new generation of inactivated polio vaccines. Chemotherapy is therefore not required for polio infections. In contrast, neither vaccines have been developed against rhinovirus infections, nor are the vaccines thought to have a use, unless broadly reacting antigenic determinants can be located. Several interesting but only weakly effective antiviral compounds have been selected against rhinoviruses and this is a major research area at present. Studies continue also with interferon, but because of toxicity problems these look less interesting at present. Sequence and biochemical data is now available for several additional enterovirus strains and this could open new possibilities both with antivirals or vaccines (for example synthetic peptides) in the near future.

Towards an in vitro model for acute hemorrhagic conjunctivitis: cytokine-mediated vascular endothelial cell activation triggered by enterovirus type 70 infection

BACKGROUND

Little is known of the pathogenetic mechanisms of enterovirus type 70 (EV70), a causative agent of acute hemorrhagic conjunctivitis. However, virus- or cytokine-induced perturbation of vascular endothelial cells are potential triggering events.

OBJECTIVE

To determine whether EV70 infection of human umbilical vascular endothelial cells (HUVECs) and human corneal epithelial cells (HCEs) causes the release of vasoactive cytokines, capable of triggering vascular endothelial cell activation.

STUDY DESIGN

Susceptibility of cultured HUVECs and HCEs to EV70 was tested by observing the appearance of cytopathic effect or immunoprecipitation of viral protein in infected cells. The culture fluids from the virus-infected cells were tested for their ability to stimulate the expression of intercellular adhesion molecule-1 (ICAM-1) on uninfected HUVECs. Anti-cytokine antibodies were used to identify ICAM-1-activating cytokine(s).

RESULTS

Both HUVECs and HCEs were susceptible to EV70 infection. Culture fluids from EV70-infected HUVECs and HCEs stimulated ICAM-l expression on uninfected HUVECs, which was completely blocked by anti-interleukin-1alpha (IL-1alpha) antibody but not by interleukin-1beta (IL-1beta) or anti-tumor necrosis factor alpha (TNFalpha) antibodies.

CONCLUSION

This study provides the first evidence of EV70 infection of both HCEs and HUVECs, and furthermore, identifies IL-1alpha as the predominant endothelial cell-activating factor produced by EV70-infected cells. Since endothelial cell activation is often an initiating step towards vascular permeability and/or inflammation, the perturbation of endothelial cell function through EV70 induced IL-1alpha is thus a potential contributory factor in the pathogenesis of EV70-associated hemorrhagic conjunctivitis.

Binding to decay-accelerating factor is not required for infection of human leukocyte cell lines by enterovirus 70

Enterovirus 70 (EV70) is one of several human enteroviruses that exhibit a propensity for infecting the central nervous system (CNS). The mechanisms by which neurotropic enteroviruses gain access to and invade the CNS are poorly understood. One possibility is that circulating leukocytes become infected and carry neurotropic enteroviruses to the CNS. We examined the ability of EV70 to infect cell lines derived from lymphoid, myeloid, and monocytic lineages. Most leukocyte cell lines tested bound radiolabeled EV70 and were permissive for EV70 replication, suggesting that EV70, in contrast to other enteroviruses, has an in vitro tropism that includes lymphoid, monocytic, and myeloid cell lines. For some of the cell lines, virus binding and infection correlated with surface expression of decay-accelerating factor (DAF), an attachment protein for EV70 on HeLa cells. However, EV70 also adsorbed to and infected cell lines that expressed little or no DAF. In contrast to what was observed for HeLa cells, neither DAF-specific monoclonal antibodies nor phosphatidylinositol-specific phospholipase C treatment inhibited EV70 binding to permissive leukocyte cell lines, and antibody blockade of DAF had little or no effect on EV70 replication. We also found that neither the human coxsackievirus-adenovirus receptor nor intercellular cell adhesion molecule 1, which mediate the entry of coxsackie B viruses and coxsackievirus A21, respectively, functions as a receptor for EV70. EV70 binding to all cell lines was sensitive to sialidase treatment and to inhibition of O glycosylation by benzyl N-acetyl-alpha-D-galactosaminide. Taken together, these results suggest that a sialylated molecule(s) other than DAF serves as a receptor for EV70 on permissive human leukocyte cell lines.

Sialic acid functions in enterovirus 70 binding and infection

The interaction of viruses with host cell receptors is the initial step in viral infection and is an important determinant of virus host range, tissue tropism, and pathogenesis. The complement regulatory protein decay-accelerating factor (DAF/CD55) is an attachment receptor for enterovirus 70 (EV70), a member of the Picornaviridae, commonly associated with an eye infection in humans known as acute hemorrhagic conjunctivitis. In early work, the EV70 receptor on erythrocytes, responsible for its hemagglutinating activity, was shown to be sensitive to neuraminidase, implying an essential role for sialic acid in virus attachment. Here, we extend these results to show that cell surface sialic acid is required for EV70 binding to nucleated cells susceptible to virus infection and that sialic acid binding is important in productive infection. Through the use of site-directed mutagenesis to eliminate the single N-linked glycosylation site of DAF and of a chimeric receptor protein in which the O-glycosylated domain of DAF was replaced by a region of the HLA-B44 molecule, a role in EV70 binding for the sialic acid residues of DAF was excluded, suggesting the existence of at least one additional, sialylated EV70-binding factor at the cell surface. Treatment of cells with metabolic inhibitors of glycosylation excluded a role for the N-linked oligosaccharides of glycoproteins but suggested that O-linked glycosylation is important for EV70 binding.

The HeLa cell receptor for enterovirus 70 is decay-accelerating factor (CD55)

Enterovirus 70 (EV70) is a recently emerged human pathogen belonging to the family Picornaviridae. The ability of EV70 to infect a wide variety of nonprimate cell lines in vitro is unique among human enteroviruses. The importance of virus receptors as determinants of viral host range and tropism led us to study the host cell receptor for this unusual picornavirus. We produced a monoclonal antibody (MAb), EVR1, which bound to the surface of HeLa cells and protected them against infection by EV70 but not by poliovirus or by coxsackievirus B3. This antibody also inhibited the binding of [35S]EV70 to HeLa cells. MAb EVR1 did not bind to monkey kidney (LLC-MK2) cells, nor did it protect these cells against virus infection. In Western immunoassays and in immunoprecipitations, MAb EVR1 identified a HeLa cell glycoprotein of approximately 75 kDa that is attached to the cell membrane by a glycosyl-phosphatidylinositol (GPI) anchor. Decay-accelerating factor (DAF, CD55) is a 70- to 75-kDa GPI-anchored membrane protein that is involved in the regulation of complement and has also been shown to function as a receptor for several enteroviruses. MAb EVR1 bound to Chinese hamster ovary (CHO) cells constitutively expressing human DAF. Anti-DAF MAbs inhibited EV70 binding to HeLa cells and protected them against EV70 infection. Transient expression of human DAF in murine NIH 3T3 cells resulted in binding of labelled EV70 and stably, transformed NIH 3T3 cells expressing DAF were able to support virus replication. These data indicate that the HeLa cell receptor for EV70 is DAF.

Coxsackie B5 papillitis

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