Giant Cell Polymyositis and Myocarditis in a Patient With Thymoma and Myasthenia Gravis: A Postviral Autoimmune Process?

Thymomas are associated with autoantibody formation. The most common are anti-acetylcholine receptor antibodies, which correspond to myasthenia gravis (MG). Other autoantibodies, such as antistriational antibodies, can occur, but their relation to clinical syndromes is frequently uncertain. The etiology of antistriational antibodies is also poorly understood. In this case, a 61-year-old man with a history of thymoma was admitted with respiratory failure. The patient was positive for anti-acetylcholine receptor antibodies and antistriational antibodies. He developed cardiogenic shock and died within 2 days despite aggressive therapy. Laboratory studies revealed elevated cardiac enzymes and marked IgG elevation against Coxsackie A virus serotypes 9 and 24. Subclinical IgG elevations against additional Coxsackie A and Coxsackie B virus serotypes were also noted. Autopsy revealed lymphohistiocytic infiltrates with multinucleated giant cells in the myocardium and skeletal muscles, including the diaphragm. Giant cell polymyositis and myocarditis is a rare, lethal complication in patients with thymoma and MG. The pathogenesis is uncertain. An autoimmune process, possibly elicited by antistriational antibodies, has been suggested. The coexistence of antistriational antibodies and Coxsackie viral serologies has not been reported. This case may suggest that giant cell polymyositis and myocarditis in patients with thymoma and MG is a postviral autoimmune process.

Role of enhanced receptor engagement in the evolution of a pandemic acute hemorrhagic conjunctivitis virus.

Acute hemorrhagic conjunctivitis (AHC) is a painful, contagious eye disease, with millions of cases in the last decades. Coxsackievirus A24 (CV-A24) was not originally associated with human disease, but in 1970 a pathogenic "variant" (CV-A24v) emerged, which is now the main cause of AHC. Initially, this variant circulated only in Southeast Asia, but it later spread worldwide, accounting for numerous AHC outbreaks and two pandemics. While both CV-A24 variant and nonvariant strains still circulate in humans, only variant strains cause AHC for reasons that are yet unknown. Since receptors are important determinants of viral tropism, we set out to map the CV-A24 receptor repertoire and establish whether changes in receptor preference have led to the increased pathogenicity and rapid spread of CV-A24v. Here, we identify ICAM-1 as an essential receptor for both AHC-causing and non-AHC strains. We provide a high-resolution cryo-EM structure of a virus-ICAM-1 complex, which revealed critical ICAM-1-binding residues. These data could help identify a possible conserved mode of receptor engagement among ICAM-1-binding enteroviruses and rhinoviruses. Moreover, we identify a single capsid substitution that has been adopted by all pandemic CV-A24v strains and we reveal that this adaptation enhances the capacity of CV-A24v to bind sialic acid. Our data elucidate the CV-A24v receptor repertoire and point to a role of enhanced receptor engagement in the adaptation to the eye, possibly enabling pandemic spread.

A viral RNA competitively inhibits the antiviral endoribonuclease domain of RNase L.

Ribonuclease L (RNase L) is a latent endoribonuclease in an evolutionarily ancient interferon-regulated dsRNA-activated antiviral pathway. 2'-5' oligoadenylate (2-5A), the product of dsRNA-activated oligoadenylate synthetases (OASes), binds to ankyrin repeats near the amino terminus of RNase L, initiating a series of conformational changes that result in the activation of the endoribonuclease. A phylogenetically conserved RNA structure within group C enteroviruses inhibits the endoribonuclease activity of RNase L. In this study we report the mechanism by which group C enterovirus RNA inhibits RNase L. Viral RNA did not affect 2-5A binding to RNase L. Rather, the viral RNA inhibited the endoribonuclease domain. We used purified RNase L, purified 2-5A, and an RNA substrate with a 5' fluorophore and 3' quencher in FRET assays to measure inhibition of RNase L activity by the viral RNA. The group C enterovirus RNA was a competitive inhibitor of the endoribonuclease with a K(i) of 34 nM. Consistent with the kinetic profile of a competitive inhibitor, the viral RNA inhibited the constitutively active endoribonuclease domain of RNase L. We call this viral RNA the RNase L competitive inhibitor RNA (RNase L ciRNA).

Sialic acid is a cellular receptor for coxsackievirus A24 variant, an emerging virus with pandemic potential.

Binding to target cell receptors is a critical step in the virus life cycle. Coxsackievirus A24 variant (CVA24v) has pandemic potential and is a major cause of acute hemorrhagic conjunctivitis, but its cellular receptor has hitherto been unknown. Here we show that CVA24v fails to bind to and infect CHO cells defective in sialic acid expression. Binding of CVA24v to and infection of corneal epithelial cells are efficiently inhibited by treating cells with a sialic acid-cleaving enzyme or sialic acid-binding lectins and by treatment of the virus with soluble, multivalent sialic acid. Protease treatment of cells efficiently inhibited virus binding, suggesting that the receptor is a sialylated glycoprotein. Like enterovirus type 70 and influenza A virus, CVA24v can cause pandemics. Remarkably, all three viruses use the same receptor. Since several unrelated viruses with tropism for the eye use this receptor, sialic acid-based antiviral drugs that prevent virus entry may be useful for topical treatment of such infections.