The Soriano Award Lecture. Emerging infections of the nervous system

Emerging issues in neurovirology: new viruses, diagnostic tools, and therapeutics

In the current era of escalating globalization with rapid transport, changing climate, and an ever growing human population with associated changes in lifestyle, poverty, and war, the emergence of new neurologic infections is accelerated. Understanding their origins using epidemiologic and molecular tools will contribute to improved control of agent spread throughout vulnerable populations. Although few interventions are effective in acute epidemics, the prompt identification of new infectious agents and the roll-out of vaccines together with new antiviral and neuroprotective drugs are promising for the management of future epidemics.

Emerging viral infections of the nervous system

New viral infections of the nervous system have been appearing with great regularity. Some result from the evolution of new agents and others from the entry of viruses into new hosts or environments. The emergence of neurovirulent enteroviruses causing a paralytic poliomyelitis syndrome and rhomboencephalitis represent the evolution of new human viruses. Most emerging viral infections represent movement of an agent into new geographic areas or across species barriers. The transport of neurovirulent strains of West Nile virus into the Western Hemisphere and the penetration of Nipah virus, a newly recognized paramyxovirus, across species barriers from bat to pig to man are examples that are highlighted in this review. The burgeoning human population and the speed and frequency of travel favor the evolution, preservation, and spread of new viral agents.

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.

Decreased parvalbumin immunoreactivity in surviving Purkinje cells of patients with spinocerebellar ataxia-1

The distribution of two calcium-binding proteins, calbindin D28k (CaBP) and parvalbumin (PV), was investigated by immunohistochemistry in the brains of three individuals dying of nonneurologic illness and three patients with spinocerebellar ataxia-1 (SCA-1). SCA-1 has recently been proven to be due to an unstable CAG repeat mutation on chromosome 6. In the cerebellum of control individuals the Purkinje cells showed strong immunoreactivity to CaBP. Other cells were CaBP-negative. Parvalbumin was highly localized to Purkinje, basket, stellate, and Golgi cells. All surviving Purkinje cells in SCA-1 were strongly immunoreactive to CaBP. The number of PV-immunoreactive Purkinje cells was markedly reduced in SCA-1. In addition, there was a significant decrease in the intensity of PV immunostaining within the individual Purkinje cells compared with controls. However, in the hippocampus, temporal cortex, and lateral geniculate scattered PV-positive neurons were seen in SCA-1 patients, similar to those in controls. The present results suggest that the decreased PV-immunoreactivity in the surviving Purkinje cells in SCA-1 may reflect biochemical alterations preceding Purkinje cell degeneration.