Bovine respiratory syncytial virus (BRSV) is a major etiological agent of respiratory tract disease in calves and results in substantial economic loss (40,45). The immune response and pathology in calves mimic symptoms caused by human respiratory syncytial virus (HRSV), which remains the leading cause of serious bronchiolitis and pneumonia in infants and young children throughout the world (9). Molecular cloning has confirmed a very close relationship between BRSV and HRSV and has revealed substantial differences from other members of the Paramyxoviridae family, leading to the establishment of the Pneumovirus genus within the Paramyxoviridae family (36, 37).As with all members of the order Mononegavirales, the 15-kb genomic RNA of RSV is contained in a ribonucleoprotein (RNP) complex which serves as a template for sequential transcription of genes (25, 49). Eleven proteins are expressed from 10 transcription units, which are arranged in the order 3Ј-NS1-NS2-N-P-M-SH-G-F-M2-L-5Ј (5, 9, 30, 31). The proteins encoded include five RNP-associated proteins, namely, the nucleoprotein N, the phosphoprotein P, the large catalytic subunit L of the RNA polymerase, and a transcription elongation factor (M2-1) encoded by the first of two overlapping open reading frames of the M2 gene (8,17,27,38). The second open reading frame of the M2 transcription unit (M2-2) was reported to encode a nonessential protein (1) which is probably involved in the regulation of RNA synthesis (4, 28). Three viral proteins are associated with the viral envelope, namely, the fusion protein F, the putative attachment protein G, and a small hydrophobic protein SH.The presence of two nonstructural protein genes, NS1 and NS2, at the 3Ј-terminal position of the genome distinguishes pneumoviruses from all other members of the Mononegavirales. Due to the 3Ј-proximal location, the NS genes are abundantly transcribed. The encoded proteins have been demonstrated in infected cells (10,16). The BRSV NS1 and NS2 genes encode polypeptides of 136 and 124 amino acids, respectively. Comparison with NS proteins of HRSV subgroup A and B proteins revealed amino acid identities of 69 and 68% for NS1 proteins and 84 and 83%, for NS2 proteins, respectively (5, 34). The deduced sequences, however, did not provide obvious clues to the function of NS proteins in the virus life cycle. The HRSV NS1 protein was reported to be associated with the M protein, while the NS2 protein did not show any detectable association with RSV structural proteins, indicating distinct functions of NS1 and NS2 (16,47). An inhibitory function of NS1 in virus RNA transcription and RNP replication was recently suggested by experiments in which artificial HRSV minigenomes were grown in the absence or presence of NS1. In the same study, an inhibitory but far less pronounced effect was also observed for NS2 (3).Recently established protocols for recovery of infectious minus-strand RNA viruses from cDNA (11) have allowed the generation of recombinant HRSV (8, 29) and BRSV (5) and allowed researchers to...

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Bovine respiratory syncytial virus (BRSV) escapes from cellular responses to alpha/beta interferon (IFN-␣Interferons (IFNs) are involved in mounting both innate and adaptive host immune responses. Genes encoding IFN-␣ and IFN-␤ are induced by virus infection or double-stranded RNA in many cell types, whereas IFN-␥ expression is restricted to activated T cells and natural killer cells. IFNs bind to independent cell surface receptors and activate distinct but related signal transduction pathways, culminating in the activation of an overlapping set of IFN-stimulated genes (ISGs) (23). A variety of ISGs code for enzymes with antiviral function, such as PKR, 2Ј-5Ј oligoadenylate synthetase, and Mx proteins. In addition, IFNs can inhibit cell growth and promote apoptosis, thereby restricting virus spread (19).To counteract IFN, viruses have evolved mechanisms that interfere with IFN induction or signaling or directly with the function of antiviral IFN-induced proteins. The speed and efficiency by which a virus circumvents IFN induction or IFN response are critical determinants for its ability to establish an infection, for its pathogenicity and host range as well as for its resistance to IFN treatment.Most members of the Paramyxoviridae family are able to affect IFN signaling using different mechanisms. Human parainfluenza virus 2 (hPIV2; genus Respirovirus) inhibits IFN signaling by degradation of STAT2 (40) whereas Sendai virus and simian virus 5 (SV5) (genera Respirovirus and Rubulavirus, respectively) do so by blocking STAT1 activation (16,24) or by promoting STAT1 degradation (8,9,15). A rather distinctive feature seems to apply to respiratory syncytial virus (RSV) of the Pneumovirus genus, as this virus, without affecting IFN signaling, was found to be highly resistant to the cellular response induced by exogenously added IFN (40).Human RSV (HRSV), the prototype of the Pneumovirus genus within the Pneumovirinae subfamily, is among the most important respiratory pathogens (5). Worldwide, HRSV is the most common cause of bronchiolitis-associated hospitalizations in infants (18,25). HRSV is also a significant cause of excess morbidity and mortality in adult patients with compromised immune status and chronic inflammatory lung disease and in the elderly (10,12,13,37). Since an effective vaccine for HRSV is not yet available, various alternative treatments such as the application of IFN-␣/␤ are being actively pursued. Sung et al. (32) reported that treatment of RSV-infected children with IFN did improve their clinical course. However, in clinical trials involving adult volunteers, recombinant IFN-2␣ did not prove to be effective as a therapeutic agent against RSV infection (21). The latter is supported by in vitro studies with both laboratory strains (1, 40) and clinical isolates of HRSV (unpublished results), which revealed a high intrinsic resistance of HRSV towards exogenously added recombinant IFN-␣/␤ in cell cultures. This applies also to the bovine counterpart of HRSV, BRSV, which causes severe losses in stock...

In the human central nervous system, susceptibility to poliovirus (PV) infection is largely confined to a specific subpopulation of neuronal cells. PV tropism is likely to be determined by cell-external components such as the PV receptor CD155, as well as cell-internal constraints such as the availability of a suitable microenvironment for virus propagation. We reported previously that the exchange of the cognate internal ribosomal entry site (IRES) within the 5′ nontranslated region of PV with its counterpart from human rhinovirus type 2 (HRV2) can eliminate the neuropathogenic phenotype in a transgenic mouse model for poliomyelitis without diminishing the growth properties in HeLa cells. We now show that attenuation of neurovirulence of PV/HRV2 chimeras is not confined to CD155 transgenic mice but is evident also after intraspinal inoculation intoCynomolgus monkeys. We have dissected the PV and HRV2 IRES elements to determine those structures responsible for neurovirulence (or attenuation) of these chimeric viruses. We report that two adjacent stem loop structures within the IRES cooperatively determine neuropathogenicity.