Avian Reovirus Major μ-Class Outer Capsid Protein Influences Efficiency of Productive Macrophage Infection in a Virus Strain-Specific Manner

Abstract

We determined that the highly pathogenic avian reovirus strain 176 (ARV-176) possesses an enhanced ability to establish productive infections in HD-11 avian macrophages compared to avian fibroblasts. Conversely, the weakly pathogenic strain ARV-138 shows no such macrophagotropic tendency. The macrophage infection capability of the two viruses did not reflect differences in the ability to either induce or inhibit nitric oxide production. Moderate increases in the ARV-138 multiplicity of infection resulted in a concomitant increase in macrophage infection, and under such conditions the kinetics and extent of the ARV-138 replication cycle were equivalent to those of the highly infectious ARV-176 strain. These results indicated that both viruses are apparently equally capable of replicating in an infected macrophage, but they differ in the ability to establish productive infections in these cells. Using a genetic reassortant approach, we determined that the macrophagotropic property of ARV-176 reflects a post-receptor-binding step in the virus replication cycle and that the ARV-176 M2 genome segment is required for efficient infection of HD-11 cells. The M2 genome segment encodes the major -class outer capsid protein (B) of the virus, which is involved in virus entry and transcriptase activation, suggesting that a host-specific influence on ARV entry and/or uncoating may affect the likelihood of the virus establishing a productive infection in a macrophage cell.The avian reoviruses (ARV) differ from the prototypical mammalian reoviruses (MRV) based on several biological properties other than just their distinct host ranges. Unlike MRV, ARV is naturally pathogenic in its avian host, lacks hemagglutinating ability, and is one of the few nonenveloped viruses capable of inducing syncytium formation in infected cell cultures and in vivo (14,18,24,28). Although ARV pathogenesis has been extensively described (5,6,15,34), the viral factors that influence ARV-host cell interactions and pathogenesis remain poorly understood.We have been investigating two ARV strains that possess distinct pathogenic and syncytium-inducing potentials. Previous results demonstrated that ARV-176 is highly pathogenic relative to ARV-138 in an embryonated egg model of virus pathogenesis, an attribute that correlates with the relative fusogenic capability of the virus (8). Both viruses infect and replicate with equal efficiency in cultured fibroblast cells, they display 94 to 98% amino acid sequence identity in the three sequenced S-class genome segment-encoded proteins (7a), and all 10 of their individual genome segments can be resolved by electrophoretic analysis (8); these properties make these two ARV strains ideal parental virus candidates for genetic and molecular approaches to identify viral determinants of host interaction and pathogenicity. We previously used a genetic reassortant approach to reveal that the S1 genome segment of ARV-176 is solely responsible for the syncytium-inducing property of the virus (8). Subsequent molecular and bio...

Detection and characterization of two co-infection variant strains of avian orthoreovirus (ARV) in young layer chickens using next-generation sequencing (NGS)

“…In ARV, the M2 genome segment encodes the major μ-class outer capsid protein (μB) of the virus, involved in virus entry and transcriptase activation 46 . The specific M2 genome segment is required for the efficient establishment of a productive ARV infection in some host cells 47 , suggesting that the same M2 segment of the two co-infection strains might be associated with ARV entry and/or un-coating in the same layer chicken host cells.…”

Piscine orthoreovirus (PRV) in red and melanised foci in white muscle of Atlantic salmon (Salmo salar)

“…Comparatively, avian orthoreoviruses (ARV) viral antigen and RNA have been documented in macrophages [ 34 ]. ARV are ubiquitous in avian farming and belong to the same genus as PRV, and virulent ARV strains have shown enhanced ability to replicate in macrophages [ 35 ].…”

Conserved structure/function of the orthoreovirus major core proteins

“…These two strains have exhibited characteristic differences with respect to their genome electrophoretic mobilities, syncytium-inducing, and pathogenic capabilities (Duncan and Sullivan, 1998;O'Hara et al, 2001). Thus, these two strains may represent some degree of diversity that exists among ARV isolates.…”

“…Finally, we have also recently determined the sequences of the ARV138 and ARV176 L2 genome segments (Xu and Coombs, 2008). Thus, to complete the entire genomic sequence determinations of two genetically distinct ARV clones that exhibit characteristic differences in genome electrophoretic mobilities, syncytium-induction, and pathogenic capabilities (Duncan and Sullivan, 1998;O'Hara et al, 2001) and which, therefore, are useful genetic reagents to further delineate ARV structure, function and pathogenesis, and to expand the available ARV sequence database, we determined the genomic sequences of the ARV138 and ARV176 L1 and L3 genome segments. These comparative sequence studies, in combination with ongoing genomic and proteomic studies, are intended to better delineate the role(s) of individual ARV proteins in the viral replication cycle.…”

“…The entire complement of S-class genome segments (for example, Chiu and Lee, 1997;Duncan, 1999;Liu and Huang, 2001;Bodelon et al, 2001;Shmulevitz et al, 2002;Kapczynski et al, 2002;Sellers et al, 2004) and M-class genome segments (for example, Touris-Otero et al, 2004;Noad et al, 2006) have been determined for some ARV clones. These sequence determinations include two strains (ARV138 and ARV176) which have served as useful genetic reagents; panels of intertypic reassortants (Duncan and Sullivan, 1998;O'Hara et al, 2001) and several temperature-sensitive mutants ) have been derived from these strains. Sequence information is also available for some ARV L1 and L3 genome segments (Hsiao et al, 2002;Shen et al, 2007) (Table 1), but not for strains ARV138 and ARV176.…”